GERMAN ATV STANDARDS W A S T E W A T E R - W A S T E

ADVISORY LEAFLET ATV-M 168E

Corrosion of Wastewater Systems - Wastewater

July 1998 ISBN 3-34984-46-0

Marketing: Publishing Company of ATV - Wastewater, Waste, and Water Management Theodor-Heuss-Allee 17 D-53773 Hennef Postfach 11 65 . D-53758 Hennef

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ATV Working Group 1.1.4 "Corrosion in Sewers" within the ATV Specialist Committee 1.1. "General Questions of Principle", which has elaborated this Advisory Leaflet, has the fol-lowing members:

Prof. Dr.-Ing. C. F. Seyfried, Hannover (Chairman) Dipl.-Ing. D. Bunge, Hamburg Dr. rer. nat. G. Heim, Hilden Dipl.-Ing. D. Kittel, Planegg Prof. Dr.-Ing. M. Lohse, Münster Dipl.-Ing. W. Meiger, Köln Dipl.-Ing. U. Neck, Düsseldorf Dipl.-Ing. G. Niedrée, Bonn (as guest) Prof. Dr.-Ing. H. Polster, Berlin Dr.-Ing. J. Rammelsberg, Gelsenkirchen Dr.-Ing. F. Schmitt, Essen Chem H. Schremmer, Dortmund (to 1994) Prof. Dr.-Ing. R. Taprogge, Hamburg

All rights, in particular those of translation into other languages, are reserved. No part of this Standard may be repro-duced in any form by photocopy, microfilm or any other process or transferred or translated into a language usable in machines, in particular data processing machines, without the written approval of the publisher.

GFA -Publishing Company of ATV - Wastewater, Water and Water Management, Hennef 1998

Original German Edition produced by: JF•CARTHAUS GmbH & Co, Bonn

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Contents

Notes for users 5

1 Introduction and determination of terms 5

2 Corrosion processes 6 2.1 Soils and groundwater 6 2.1.1 Natural soils 6 2.1.2 Artificial soils 7 2.2 Wastewater 7 2.3 Sewer atmosphere 7

3 Construction and other materials 9 3.1 Cement bonded materials 9 3.1.1 Concrete and reinforced concrete 10 3.1.1.1 General 10 3.1.1.2 Chemical loading due to communal wastewater 10 3.1.1.3 Loading in the sewer atmosphere 14 3.1.1.4 Loading through soil and groundwater 14 3.1.1.5 Information on the avoidance of reinforcement corrosion 14 3.1.2 Mortar 15 3.1.3 Fibre cement 16 3.1.4 Composite pipes 16 3.2 Vitrified clay, sewer brick, glass 16 3.3 Metallic materials 17 3.3.1 Unalloyed and low alloy iron materials 17 3.3.1.1 Linings for pipes made from ductile cast iron and steel 17 3.3.1.2 Sheathing 18 3.3.2 High alloy, stainless steels 18 3.4 Plastics (PVC-U, PE-HD, PP, GFRP) 21 3.4.1 Preamble 21 3.4.2 Pipe materials 22 3.5 Sealing materials 24 3.5.1 General requirements on sealing materials for wastewater systems 24 3.5.2 Materials for and properties of sealing materials 24

4 Corrosion protection 25 4.1 Compound materials and linings 25 4.1.1 Pipe linings with new constructions 25 4.1.1.1 Factory produced pipe lining using PVC plasticised films 25 4.1.1.2 Factory produced pipe lining using unplasticised PVC web sheets 26 4.1.1.3 Factory produced pipe lining using web or knob HDPE sheets 26 4.1.1.4 Factory produced pipe lining using vitrified clay shells (ceramic plates) 26 4.1.1.5 Retrofitted pipe lining using plastic sheets 27 4.1.2 Shaft linings with new constructions 27 4.1.2.1 Factory produced shaft lining using plastic sheets 27 4.1.2.2 Shaft lining using GFRP sheets and elements 27 4.1.2.3 Shaft lining using sewer bricks 28

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4.1.3 Pipe linings with renovation 28

4.1.3.1 Renovation of non-man accessible profile sections 29 4.1.3.2 Renovation of man accessible profile sections 29 4.1.4 Shaft linings with renovation 29 4.2 Protective paints and coatings 30 4.2.1 Coatings on iron materials 30 4.2.2 Coatings on concrete surfaces 30

5 Notes for planning and operation 31 5.1 Notes on planning 31 5.1.1 Preamble 31 5.1.2 Location of wastewater treatment systems 31 5.1.3 Composition of wastewater 31 5.1.4 Indirect discharger operations 32 5.1.5 Drainage systems 32 5.1.6 Gravity pipelines 32 5.1.7 Pump stations and cross-sectionally filled pipelines 34 5.1.8 Soil and groundwater conditions 36 5.2 Addition of chemicals 37 5.2.1 Fundamentally suitable means 37 5.2.2 Addition of compressed air and pneumatic delivery 37 5.2.3 Addition of pure oxygen 39 5.2.4 Hydrogen peroxide 40 5.3 Operational measures 41 5.3.1 Cleaning and maintenance 41 5.3.2 Measures with the occurrence of corrosion 41 5.3.3 Measures in pump sumps and pressure pipelines 42

6 Bibliography 42

7 Applicable Standard Specifications 45

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Notes for Users This ATV Standard is the result of honorary, technical-scientific/economic collaboration which has been achieved in accordance with the principles applicable for this (statutes, rules of procedure of the ATV and ATV Standard ATV-A 400). For this, according to precedents, there exists an actual presumption that it is textually and technically correct and also generally recognised. The application of this Standard is open to everyone. However, an obligation for applica-tion can arise from legal or administrative regulations, a contract or other legal reason. This Standard is an important, however, not the sole source of information for correct solu-tions. With its application no one avoids responsibility for his own action or for the correct application in specific cases; this applies in particular for the correct handling of the mar-gins described in the Standard.

1 Introduction and Determination of Terms It is only recently that wastewater networks have been inspected systematically, whereby corrosion damage has been increasingly found (KEDING et al., 1990; MATTHES, 1992; STEIN and KAUFMANN, 1993). According to a census taken by ATV (German Associa-tion for the Water Environment) on the condition of sewer systems in Germany, corrosion was named as the fourth most frequent cause of damage in the Federal Republic of Ger-many behind the formation of cracks and fragments, leaks and blockages to the flow(KEDING et al., 1990). Until recently there has been extensive uncertainty on the part of planners and wastewater system operators on corrosion questions. Therefore the term "Corrosion" is first to be defined:

"In the field of wastewater treatment systems, one understands under "corrosion" all reac-tions on non-metallic construction materials and materials with their environment which, through chemical, electro-chemical or microbiological processes lead to a prejudicing of the construction material or material.

Damage as a result of mechanical effects such as wear, erosion or frost are to be consid-ered separately. It cannot be excluded that such damage which is designated as "corro-sion" is caused by a combined loading of chemical, microbiological and chemical effects."

Due to a lack of knowledge on corrosion processes and material properties, gravity pipe-lines, pressure pipelines and pump sumps are today still being incorrectly conceived in the same way as 50 years ago. The taking into consideration of a possible corrosion is not easy in particular due to the numerous materials used in sewerage system construction and the complex processes. It could also be associated with the fact that, previously in Germany, there has been no complete set of rules and standards available for the avoid-ance of corrosion damage in wastewater systems.

This Advisory Leaflet has been elaborated by a group of experienced specialists from re-search, industry, planning and sewerage system operations. Its objective is:

− to compile the status of today's knowledge on materials, operational conditions, in sew-ers and in corrosion processes,

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− to give information on planning, construction and operation to ensure the durability and functional safety of sewers during their planned useful life of 50 - 80 (100) years (LAWA, 1993),

− to assist the practician with the selection of suitable materials if particular and hard to estimate parameters exist.

Recommendations for renovation are not part of this Advisory Leaflet, however, these can be taken from ATV Advisory Leaflet ATV-M 143.

2 Corrosion Processes 2.1 Soils and Groundwater

The constitution and thus the possible corrosive properties of a groundwater stand in direct relation to the chemical and physical properties of the soil with which the groundwater or the precipitation water that has percolated into the subsoil comes into contact. The mate-rial damaging components can only then take effect if they are dissolved by the soil water and thus come into contact with the structure.

2.1.1 Natural Soils

With natural soils the coherence is not only of significance in combination with the water content but also with regard to the oxygen content. In the porous and loose soils the oxy-gen content reduces less quickly with increasing soil depth than with highly cohesive soils which, particularly with high water contents, are rather impermeable to air. With the pres-ence of oxygen one talks of aerobic and with the absence of oxygen of anaerobic soils.

While oxygen is of great significance with attacks on unprotected metallic materials, with cement bonded materials it only has a role insofar as certain chemical and biological proc-esses, which can lead to the formation of corrosive substances (e.g. sulphur dioxide) are dependent on it.

With natural soils only a few inorganic substances, in the first instance sulphates, chlorides and excess free carbon dioxide as well as organic substances, e.g. humic acid, come into consideration as corrosive groundwater content substances.

High sulphate contents are to be found in the groundwater of soils which are heavily per-meated by gypsum or anhydrite (gypseous marl or shale). Chlorides are frequently found in the vicinity of marshy soils, salt pans or with country roads spread with salt. The excess carbon dioxide found in groundwater, which attacks unprotected metallic and cement bonded pipe materials has its origin primarily in the biological metabolisation of organic substances present in the upper soil layers. If the carbon dioxide manages to penetrate into the subsoil with percolated precipitation water and, depending on the soil type, finds no reaction partner (e.g. calcium, magnesium), then it lowers, as dissolved aggressive carbon dioxide in water, the pH value of the soil water. It behaves in a similar fashion to "acid rain" which, inter alia, is caused by SO2 emissions. This phenomenon is receiving increasing attention in specialist publications and seminars (HANTGE, 1993; WALTHER, 1994). Soil suspensions with pH values < 4 in depths of from 1.5 to 2 m are no rarity.

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2.1.2 Artificial Soils

With artificial soils, to which belong, for example, accumulations of refuse, construction rubble, industrial slag and rocky material resulting from mining operations, high contents of material corrosive substances can occur in the groundwater.

If a soil exchange with such materials is to take place with the backfilling of pipeline trenches, a specialist report on the suitability of the material is to be obtained. However, this may not limit itself to an assessment from the aspect of construction material corrosion alone. It must also contain details on the water soluble substances from which a hazarding of the groundwater can stem. This is to be observed particularly with some of the recycling materials offered today.

2.2 Wastewater

Wastewater is to be designated and classified according to its origin: domestic, commer-cial and industrial wastewater; contaminated precipitation water. With common discharge of wastewater one talks of communal wastewater (EN 1085/DIN 4045).

The basic loading of wastewater with inorganic substances results from the composition of the drinking or service water. Depending on the usage of the water - above all in the com-mercial and industrial area - wastewater can contain various material corrosive sub-stances.

According to communal bylaws no substances may be discharged with the wastewater which can prejudice the stability of public wastewater systems. According to ATV Standard ATV-A 115, discharge limitations exist in particular for pH values (6.5 - 10), for sulphates (600 mg SO4/l) and for the wastewater temperature (35 °C).

In general stormwater causes no chemical attack. In special cases in which the stormwater cannot be buffered in natural paths there is a possibility of a corrosive attack.

From experience, account must be taken of possibly aggressive wastewater contents, de-spite the discharge limitations set by bylaw for commercial and industrial discharges, as the operator of public wastewater systems is also liable for subsequent damage, which result from unlawful discharge of wastewater, if the originator cannot be traced. Therefore corrosion resistant materials should be employed in industrial areas (IMHOFF, 1993).

2.3 Sewer Atmosphere

The atmosphere in enclosed wastewater systems is, in general, marked by a high humidity with a tendency to the formation of condensation water. Through this, with unprotected metallic materials, corrosion can occur. The presence of hydrogen sulphide leads, in wet places above the water level to the formation of sulphuric acid with a correspondingly high degree of corrosion with cement bonded and unprotected metallic construction materials. The biogenic sulphuric acid corrosion (BSAC) is induced mainly through the biological conversion of sulphate sulphur into sulphides under anaerobic conditions in the underwa-ter area, rarely also through sulphide (H2S, HS- and S2-), which are discharged by indus-trial concerns. To avoid conditions which can lead to BSAC see Chap. 5, in which informa-tion for practical planning and a technically correct operation are given. In simple terms the mechanism of sulphate conversion and BSAC can be described as follows:

− biological reduction of sulphates and other sulphur components to sulphides (H2S, HS- and S2-) in the wastewater under anaerobic conditions;

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− release of hydrogen sulphide gas into the atmosphere which dissolves on the wet sewer wall;

− biological oxidation of the H2S dissolved on the construction material surface above the water level to sulphuric acid and elemental sulphur.

The degradation processes in a sewer under aerobic conditions are shown in the left-hand side of Fig. 1. The reduction of sulphates and albuminous compounds from the wastewater take place in the sewer film and in deposits. If the dissolved oxygen is assimilated (with sewer films already at a few tenths of a millimetre) the reduction of the sulphate to sul-phide due to the strict anaerobic desulphuricants begins. The sulphide diffuses in the di-rection of the wastewater, whereby it has to pass the upper, aerobic layer of the sewer film or the deposits. Here it is again oxidised to sulphate before it reaches the wastewater. Un-der aerobic conditions, although a sulphur reduction takes place in the depth of the sewer film and the deposits, the reduced sulphur compounds are nevertheless again oxidised before reaching the wastewater.

Under anoxic or anaerobic wastewater conditions a reduction of sulphate already takes place in the upper layers of the sewer film and deposits. The from this resultant sulphides can then diffuse, unhindered, into the wastewater. Depending on the pH value of the wastewater there is a balance between H2S and HS-. With normal pH values in the waste-water between pH 7 and 8, the hydrogen sulphide component can be between 50 and 10 %. The lower the pH value the greater is the share of H2S in the total sulphide and the greater is also the H2S potential that can be released into the atmosphere and which, in addition to corrosion, can lead also to odour problems and endangering of life.

With regard to the valuation of the sulphide present in the wastewater it must be taken into account that, only from the dissolved sulphides does a pH dependent part exist as hydro-gen sulphide, which can escape in the form of gas and lead to corrosion. The determina-tion of the dissolved sulphide takes place according to DIN 38 405, Part 26.

If sulphides are present in the wastewater a part will, however, also exist in undissolved form (bonded on metals). Thus, for example, the black colour of digested wastewater can be traced back to finely distributed iron sulphide. The undissolved sulphides can, with normal wastewater conditions, cannot contribute to the production of hydrogen sulphide. If these are determined by the examination of the wastewater (which is often the case with conserved wastewater samples), a reduction for the undissolved sulphides from the de-termined total sulphide content must take place. With an extensively digested domestic wastewater one can set the content of undissolved sulphides at some 50 % of the total sulphide contents.

Due to diffusion and turbulence the hydrogen sulphide gas is released into the sewer at-mosphere and then dissolves on the wet sewer wall. With time it forms into a biofilm in which also the very acid tolerant thiobacilli occur. They are capable of oxidising the hydro-gen sulphide into sulphuric acid. Particularly in the warm and low discharge seasons there is an enrichment of the biogenically formed sulphuric acid, mainly in the crowns of the pipe which, with very low pH values, are subjected to heavy chemical attack.

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Fig. 1: Sulphate conversion in sewers

3 Construction and Other Materials

3.1 Cement Bonded Materials

The construction material or material concrete, mortar and fibre cement consist in general of the hydraulic bonding means cement, mineral additives and/or fibres and water. Proc-essing and employment characteristics are deliberately influenced using additional con-crete agents or concrete additives. Cement bonded construction materials are employed in numerous forms with different structures for wastewater collection, delivery and treatment.

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In addition to the technical usage characteristics of concrete such as stability, imperme-ability, temperature and dimensional stability, the chemical resistance is of significance with regard to durability.

As a rule, with cement bonded construction materials, corrosion processes are long-term. The scope of corrosion is, in the first instance, influenced by the concentration of the at-tacking substances, the delivery conditions and the reaction time. With wastewater sys-tems, with regard to the chemical attack, the reactions and the loading due to the waste-water on the pipe channel surface (see Sects. 3.1.1.2 and 3.1.1.3) and the loading due to the soil and groundwater on the outside of the component or pipe (see Sect. 3.1.1.4) are to be differentiated.

3.1.1 Concrete and Reinforced Concrete

3.1.1.1 General

Concrete can be used as locally produced concrete or in the form of prefabricated compo-nents. The concrete components can be reinforced - mild steel reinforcement or prestressed - or unreinforced. The Standard Specification DIN 1045 "Structural Use of Concrete; Design and Construction" applies for the production and dimensioning of the concrete. Concrete for components, which are employed in drainage facilities, is to pro-duced in accordance with the specifically applicable Standard Specification DIN 4281 "Concrete for Drainage Units; Manufacture, Requirements and Testing, (3/1985)".

Concrete with special composition, e.g. addition of fine particles or use of special cements, meet higher demands on stability, permeability and chemical resistance (see Sect. 3.1.1.2).

The most important standard specifications for prefabricated concrete components for em-ployment in sewerage networks are:

DIN 4032 Concrete Pipes and Fittings

DIN 4034 Shafts constructed from Prefabricated Concrete and Reinforced Concrete for Underground Drains and Sewers

DIN 4035 Reinforced Concrete Pipes, Reinforced Concrete Pressure Pipes and Asso-ciated Fittings

3.1.1.2 Chemical Loading Due to Communal Wastewater

For the chemical loading of concrete due to communal wastewater (see Sect. 2.2) and the possible advance of corrosion through this, in addition to concentration and reaction time, the high flow rate of the wastewater in comparison with the regulations of DIN 4030 and the frequency of cleaning processes with their mechanical influences on the surface of the concrete, play a role. Therefore, the limiting values in Tables 1 and 2 are not identical with the limiting values Table 4 of DIN 4030. The size of the limiting values given in Tables 1 and 2 for the concentration of the aggressive substances is so determined that the pipe-lines remain, in the long-term, free of damage; with this the longest service life is based according to the LAWA Guidelines (LAWA, 1993).

A. Limiting values with permanent loading (normal case)

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A sufficient resistance of concrete to corrosion loading in the wastewater area (see Sect 2.2) is ensured if wastewater does not exceed the limiting values given in Table 1 with re-gard to concrete aggressive content substances. For wastewater content substances for which standard values exist in ATV Standard ATV-A 115 "Discharge of Non-domestic Wastewater into a Public Wastewater System“, October 1994, the limiting values agree in the main with the standard values (Column 4).

In Column 3 are listed the amounts of wastewater components (extent of the steady load), which come into question for chemical loading which, from experience, occur with normal communal wastewater. In the normal case the amounts lie clearly below the limiting val-ues. This also applies for stormwater runoffs.

In individual cases such as, for example, in mountainous regions with a small buffer ca-pacity of the soil, increased spring water runoffs with increased acid content, e.g. with car-bon dioxide or humic acid (Schwarzwald), can occur. In such a case the amount of the loading (concentrate, duration) are to be assessed separately.

With the loading through normal communal wastewater a sufficient chemical resistance of the concrete exists if the concrete meets the requirements of Table 1, Column 5.

With an increased chemical loading of the concrete through communal wastewater, as can occur according to Sect. 2.2, sufficient resistance exists for concrete pipes and shaft com-ponents up to a pH value > 4.5 if the concrete, for example, meets the following additional requirements:

− high performance concrete with a strength class ≥ C 75/85 using highly reactive poz-zolanic fine grain materials, such as, for example, silicate dust, with at least 5 % of the quantity of the bonding means and/or appropriately constituted special cements; water-cement ratio w/c: ≤ 0.45, water ingress depth (DIN 1048): ≤ 2.0 cm)

− employment of alumina cement as bonding agent,

and the pipes and shaft components are examined and monitored according to the "FBS Quality Guideline - Concrete Pipes, Reinforced Concrete Pipes, Service Pipes and Shaft Components for Underground Drains and Sewers (Published by the "Fachvereinigung Betonrohre und Stahlbetonrohre e.V. [Specialist Association for Concrete Pipes and Rein-forced Concrete Pipes], Bonn) (also available in English).

B. Limiting values for temporary or short-term loading (special case)

From experience, with the discharge of wastewater, the discharge conditions can be so changed through, for example, misuse, mishandling, unforseeable failure (accident) or long-term conversion of technical facilities, that the discharge limiting values cannot al-ways be met. Through this, the limiting values given in Table 1 for long-term loading, can be temporarily exceeded or undercut. Therefore, the limiting values for temporary or short-term higher permitted loadings are listed in Table 2 for concrete corrosive wastewater con-tent substances, by which no damage to the concrete is to be expected with the fulfilment of the requirements, laid down in Table 2, on the concrete composition during the longest service life in accordance with the LAWA Guidelines (LAWA, 1993).

Table 1: Limiting values for a long-term loading of concrete in the sewer network through communal wastewater

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Type of attack Attacks through, for example

Loading parameters of normal communal wastewater

Sufficient concrete resistance exists:

with a long-term load with fulfilment of fol-lowing requirements on the concrete

Limiting values in wastewater

1 2 3 4 5

Loosening through leaching

Soft water Not given Not applicable

Loosening through acid attack

Inorganic and organic acids

pH value: 6.5 to 10 pH value ≥ 6.5 w/c ≤ 0.502) and water ingress depth

Lime dissolving car-bon dioxide (CO2)

< 10 mg/l1) ≤ 15 mg/l (DIN 1048) of ≤ 3 cm

Loosening through Magnesium (Mg2+) < 100 mg/l ≤ 1000 mg/l

exchange reaction Ammonia-nitrate (NH4-N)

< 100 mg/l ≤ 300 mg/l

Swelling Sulphate (SO42-) < 250 mg/l ≤ 600 mg/l As above without HS

cement

< 3000 mg/l As above with HS cement

1) In normal communal wastewater this value is not achieved. At most, in individual cases, a value in the given order is possible with the discharge of large quantities of groundwater containing carbon dioxide (e.g. drainage water).

2) The resistance of the concrete is considerably enhanced through low w/c values and through the use of cement with special composition.

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Table 2: Limiting values for a temporary or short-term loading of concrete in the sewer network through communal wastewater

Attack, for example, through Sufficient resistance of concrete exists with a loading

Temporary1) Short-term2) With fulfilment of following

Limiting values in wastewater Requirements on the concrete

1 2 3 4

Soft water Not applicable Not applicable

Inorganic acids, e.g. sulphuric acid, hydrochloric acid, nitric acid

pH value: ≥ 5.5 pH value: ≥ 4 w/c ≤ 0.503) and water ingress depth (DIN 1048) ≤ 3 cm

Organic acids pH value: ≥ 6 pH value: ≥ 4

Lime dissolving carbon dioxide (CO2)

≤ 25 mg/l ≤ 100 mg/l

Magnesium (Mg2+) ≤ 3000 mg/l

Ammonia-nitrate (NH4-N)

≤ 1000 mg/l No limitation

Sulphate (SO42-) ≤ 1000 mg/l As above without HS cement

≤ 5000 mg/l As above with HS cement

1) Duration up top a maximum of one year per ten years. 2) Unscheduled operational conditions; duration up to a maximum of one hour per week. 3) The resistance of the concrete is considerably enhanced through low w/c values and through the use of cement with special

composition.

1. Under "temporary" loading (Column 2) one understands a loading which, during longer periods of time, e.g. between two inspection dates during the course of ten operational years, exercises an effect in the order of a maximum of one year. These special condi-tions can be scheduled for necessary tasks on technical installations, which unavoid-ably stretch over a longer period.

2. To cover unscheduled operational conditions, with which higher loading occurs for a short time, the limiting values listed under "short-term (Column 3) apply. Such short events are seen as non-critical if they occur, at the most, once a week for a maximum of one hour.

Note:

One-off, surge type discharges of concrete corrosive substances with higher concentra-tions, which occur over a very short term through misuse or accident (discharge in gushes) is, as a rule, irrelevant with regard to a chemical attack on the concrete.

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3.1.1.3 Loading in the Sewer Atmosphere

If a chemical attack on concrete takes place in the sewer atmosphere then this, as a rule, is a biogenic sulphuric acid attack (see Sect. 2.3). With biogenic sulphuric acid corrosion the sulphuric acid attacks the concrete chemically above the wastewater level causes a loosening attack on the surface of the concrete. The sulphates which result as reaction products simultaneously with the loosening attack on the concrete can, in principle, effect an expanding chemical attack in areas close to the surface (see also Sect. 3.1.1.4). One can, however, assume that with a very low pH value the loosening attack and not the sul-phates resulting from the reaction determines the rate for a corrosion of the concrete. With expected biogenic sulphuric acid attack a concrete with special composition in accordance with Sect. 3.1.1.2 should be used.

3.1.1.4 Loading through Soil and Groundwater

The chemical loading of concrete components of a wastewater network through soil and groundwater is to be assessed and classified with regard to the degree of attack in accor-dance with DIN 4030 "Assessment of Soil, Water and Gases for their Aggressiveness to Concrete; Principles and Limiting Values " (6/91). The respective necessary technical re-quirements and measures for concrete, which ensure a long-term damage-free condition, are contained in the concrete standard specifications.

In connection with the information in Sect. 2.1.1 on the corrosion processes in natural soils, which are initiated through sulphates or lime dissolving carbon dioxide, the funda-mental reactions occurring with these are described below in more detail.

Sulphate

Due to solutions containing sulphate the aluminates and aluminate hydrates in the hard-ened cement paste can, for example, react as follows under the formation of trisulphates (ettringite) containing a great deal of crystal water:

3 CaO . AL2O3 + 3 (CaSO4 . 2 H2O) + 26 H2O → 3 CaO . AL2O3 . 3 CaSO4 . 32 H2O)

Through the subsequent crystallisation and the growth of the reaction products a pressure develops in a fixed layer, which leads to swelling effects. Here, the formation of ettringite and gypsum should be mentioned.

Lime dissolving carbon dioxide

With the chemical attack of lime dissolving carbon dioxide, following an initial compaction through the formation of the slightly soluble calcium carbonate according to

Ca(OH)2 + CO2 → CaCO3 + H2O

with a further effect of water containing CO2, there is a formation of slightly soluble cal-cium hydrogencarbonate

CaCO3 + CO2 + H2O → Ca(HCO3)2.

Ca(HCO3)2 is dissolved by water and is carried away.

Aqueous solutions of CO2 react slightly acidic (carbonic acid). The corrosive effect of dis-solved carbon dioxide is here dependent on the hardness of the water; the greater this is

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the more stabilising carbon dioxide is required in order to keep the hydrogen carbonate in solution. This means that, in hard water, there must first be a high content of free carbon dioxide to have a damaging effect as opposed to soft water which, already with slight car-bon dioxide content, can be aggressive against concrete.

3.1.1.5 Information on the Avoidance of Reinforcement Corrosion

With concrete components for wastewater systems there is a satisfactory corrosion protec-tion for the reinforcement if the requirements for the concrete covering dimensions and the crack width limitation, laid down in DIN 1045 or in DIN 4035, DIN 4034 and DIN 4281, de-pending on the strength of the concrete, and on the environmental conditions in accor-dance with DIN 1045, Table 10, Line 3, are met. As a rule, the concretes of components used in wastewater systems are very impervious. Therefore, for example, the possible chloride content of normal communal wastewater does not promote corrosion. The general preconditions for a corrosion of the reinforcement, i.e. the carbonating of concrete and ad-dition of oxygen, do not exist with the permanently wet location conditions for components in the area of the wastewater. Therefore, with impervious concrete, no corrosion of the reinforcement can take place here.

3.1.2 Mortar

In general mortar is employed in wastewater systems as brick and joint mortar, as mortar for the repair of components or for purposes of lining pipes (see also Sect. 3.3.1.1). The composition of the mortar depends on required unset and set mortar properties. As a rule, hydraulic mortars of Mortar Groups IIa, III, IIIa according to the Brickwork Standard Speci-fication DIN 1053, are used for wastewater components.

With cement bonded mortars important properties such as impermeability, adhesion as well as mechanical and chemical resistance can be improved with the aid of suitable syn-thetic additives. Such synthetically modified cement mortars are to be selected and applied according to the DAfStb [Service Instructions for Registrars and Supervisory Authorities] Standard for the Protection and Repair of Concrete Components (8/90). Depending on the type of mechanical loading to be expected in the sewer, mortar of Loading Classes M3 or M4 as listed in the Standard can be considered., The Standard contains requirements on the set mortar and details on the required verification.

The specialist technical rules are to be observed with the processing of mortar, so that an as impermeable as possible constitution is produced. The mortar must be processed be-fore the start of setting, full width and thickly applied and protected, e.g. from draughts in the sewer, against rapid drying out. For good bonding between the mortar and the sub-surface care is to be taken, for example through careful cleaning of the sub-surface, by the removal of all loose components and by wetting. With the use of mortar systems attention is to be paid to the manufacturer's processing instructions which, as a rule, include the necessary preparation of the sub-surface.

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3.1.3 Fibre Cement

Fibre cement is produced from cement and water with the addition of synthetic fibres as reinforcement and, for example, of pulp fibres as retention aid. In the hardened condition the fibres firmly embedded in the cement matrix increase the tensile strength of the fibre cement. Due to the dewatering of the cement lime, connected with production, a very im-pervious cement composition results with very favourable water-cement ratios. Through this, the limiting values in accordance with Tables 1 and 2 can also be applied to fibre ce-ment. In exceptional cases, special cements, in particular sulphate resistant cements, can be employed. The most important standard specifications for prefabricated components made from fibre cement for employment in wastewater networks are:

DIN 19 840 Faserzementrohre und -Formstücke für Abwasserleitungen [Fibre Cement Pipes and Fittings for Drains] Parts 1 and 2

DIN 19 850 Faserzementrohre und -Formstücke für Abwasserkanäle [Fibre Cement Pipes and Fittings for Sewers, Parts 1 and 2: Pipes, Joints, Fittings, Part 3: Shafts.

3.1.4 Composite Pipes

So-called composite pipes with improved load bearing capacity result from the concrete envelopment of, for example, vitrified clay pipes or plastic pipes. Such composite pipes are, as a rule, produced in concrete factories. They are used with particularly high static and dynamic loading as well as in cases in which the particular protection of a concrete pipe is necessary for technical wastewater reasons. The thickness of the concrete enve-lope can be matched to the static loading. According to plan, with such composite pipes, the concrete does not come into contact with the wastewater. The provisions of DIN 4030 "Assessment of Soil, Water and Gases for their Aggressiveness to Concrete" apply with regard to a chemical attack on the outside of the composite pipe due to the soil or ground-water.

3.2 Vitrified Clay, Sewer Brick, Glass

Vitrified clay pipes and fittings in accordance with DIN EN 295, Part 1, are manufactured from suitable clay and fired to vitrification. The material properties are described and de-fined in their requirements (e.g. annealing loss, water absorption, texture and abrasion resistance) supplementary to DIN EN 295, in Works Standard WN 295. Pipes and fittings can be glazed or unglazed on the inside and/or outside. With the exception of hydrofluoric acid they are not attacked by substances contained in the wastewater or in the groundwa-ter soil. If verification is required in the individual case this takes place in accordance with EN 296.

Sewer bricks, in accordance with DIN 4051 are used for structures and, in part, for large dimensioned sewers. Using clays they are formed mechanically and fired to vitrification. As sewer bricks are resistant against chemical attack the quality of the mortar used and its technically correct processing has particular significance (comp Sect. 3.1.2).

Until now glass has been employed only in trials in the form of shells as lining material for concrete pipes. It also has a very high chemical resistance which, however, is to be veri-fied in special cases.

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3.3 Metallic Materials

3.3.1 Unalloyed and Low Alloy Iron Materials

The metallic materials used in the construction of underground sewers and wastewater pressure pipelines are essentially unalloyed and low alloy steels and ductile cast iron.

These materials and the thereform produced sewers can, unprotected, suffer corrosive attacks internally due to the flowing medium as well as through the type of the sewer at-mosphere and externally through the soil and/or its content substances. Components made from steel and ductile cast iron are therefore to be employed only with satisfactory corrosion protection.

Table 3: Limiting parameters of the areas of application of cement mortar linings of ductile cast iron pipes, steel pipes and fittings taking onto account DIN 2614 (permanent loading)

Parameters in the flowing medium Unit Type of lining according to DIN 2614 I - S

(Blast furnace or Port-land cement) (HOZ or PZ)

I - T (Alumina cement (TZ))

pH value*) - 6.5 - 12 4.5 - 12 Mg2+ mg/l ≤ 1000 solubility limit SO4

2- mg/l ≤ 3000 solubility limit NH4

+ mg/l ≤ 200 ≤ 2000 Ca2+ mg/l ≥ 1 ≥ 0

(stormwater) Lime dissolving carbon dioxide mg/l ≤ 7 solubility

limit(stormwater) Parameters in the sewer atmosphere H2S concentration in the free cross-section of the sewer as measure for the BSAC**)

ppm < 0.5 0.5 - 10

*) Short-term undercutting causes no damage **) According to the current status of knowledge, it is generally assumed that below 0.5 ppm H2S in the sewer atmos-

phere one does not have to reckon with biogenic sulphuric acid corrosion. Already with H2S concentrations upwards from 0.5 ppm in the sewer atmosphere heavy degrees of attack by BSAC can occur (BIELECKI and SCHREMMER, 1987). The correlation between H2S concentration and strength of attack was found using simulation in the pollution gas chamber (SAND, 1987), the same relationship was verified by SEYFRIED (in: BELECKI and SCHRAMMER, 1987) for conditions in practice. With a H2S content of 10 ppm is designated as heavy (BOCK et al., 1990).

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3.3.1.1 Linings for Pipes Made from Ductile Cast iron and Steel

Cement mortar linings in ductile cast iron pipes have been used for over 120 years, they were originally employed to prevent corrosion damage in pipelines from aggressive drink-ing water. According to DIN 2614 there are three procedures for the manufacture of ce-ment mortar linings:

− rotary centrifugal casting process (Procedure I) − centrifugal application process (Procedure II) − manual lining (Procedure III) for repairs, completion of lining during pipe construction

and partially for the lining of fittings.

Wastewater pipes (DIN EN 598) are fundamentally lined using the rotary centrifugal proc-ess, whereby the mortar is highly compacted. Through this there is a double corrosion pro-tection effect of the mortar lining:

1. The alkalinity of the pore water with a pH value > 9 passivates the underlying iron sur-face and thus prevents corrosion (active component).

2. The compact mortar structure (high rotation speed - driving out of batch water - w/c ratio ca. 0.3) hinders the diffusion of the oxygen to the iron (passive component).

For cement mortar lining in accordance with DIN 2614, essentially sulphate resistant blast furnace and Portland cements in accordance with DIN 1164 (S in accordance with DIN 2614) as well as alumina cement in accordance with British standard BS 915 (T in accor-dance with DIN 2614) are used. With concrete aggressive wastewater or with an antici-pated biogenic sulphuric acid corrosion (BSAC), the alumina cement (TZ) mortar lining (T) is to be applied. The long-term protective effect on linings using organic substances de-pends very much on the adhesive ability of these substances on to internal metal surfaces. Many years practical experience has shown that, due to the unavoidable permeation of oxygen, water vapour and carbon dioxide through the organic substances, the adhesive capability can, in the long-term, be lost (e.g. polyurethane, polyurethane tar, polyethylene etc.).

3.3.1.2 Sheathing

The corrosion probability of a soil against unalloyed and low alloy steels and ductile cast iron is determined according to DIN 30 672, Part 3. From the sum of various analytically determined assessment figures a division of soils into aggressiveness classes or Soil Classes I to III is possible.

For on-site post sheathing of the pipe connections with soil of Soil Class III, sheathings made of anti-corrosion bands, heat shrinkage material in accordance with DIN 30 672, Part 1 or rubber collars are used. DIN 30 675, Parts 1 and 2 give information on corrosion protective measures and the sheathings to be used according to the soil class.

3.3.2 High Alloy, Stainless Steels

High alloy, stainless steels belong to a comprehensive material group and are resistant with many corrosion loads. The resistance is governed by a very thin passive layer. The even surface abrasion with values < 10 µm per year in the passive area is negligibly small. The passivity is essentially determined by the content of chromium which gives this steel its passivity. In addition to the chromium content the other alloying elements of significance are, for example, nickel and molybdenum.

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In the first instance, for employment in wastewater systems, austenitic chromium-nickel steels with and without molybdenum addition come into consideration. In a draft for an European Standard Specification (pr EN 1990) there are three often applied steel qualities, whose most important details are contained in Table 4. According to pr EN 1990, there are thus other comparable steel qualities which are permitted.

Pitting - as with other materials with passive layers (e.g. Cu, Al) - can occur with the pres-ence of large quantities of chlorides. With this it is not only the chloride contents of the wastewater which are significant; chloride can also accumulate in fixed deposits on steel surfaces even with wastewater with non-hazardous chloride contents. In these cases, with potentials which are greater than the pitting potential UL, there is a break through of the passive layer with pitting as a result. It is pointed out, that also with atmospheric corrosion loads, corrosion hazardous chloride accumulations can occur in fixed deposits.

Table 4: Characteristics of some important stainless steels

Material designation Masses %

ISO 683/ 13-

1986

Euronorm SS-71

Material No.

C Cr Ni Mo - Effec-tive

sum in masse

s %

Pitting potential

UL in mV1)

a b c d e f g h i j

11 X6 Cr Ni5) 18 10

1.4301 (V2A)2)

≤ 0.07 17 to 19 8 to 11 - - 18 + 250

19 X3 Cr Ni Mo 17 12 2

1.4435 ≤ 0.03 16 to 18.5

11 to 14 2.0 to 2.5 - 25 + 600

21 X3 Cr Ni Mo Ti 17 12 2

1.4571 (V4A)2)

≤ 0.08 16 to 18.5

10.5 to 14

2.0 to 2.5 5 % C ≤ Ti ≤ 0.5

25 + 6003)

- X3 Cr Ni Mo N 17 13 54)

1.4439 ≤ 0.04 16.5 to 18.5

12.5 to 14.5

4.0 to 5.0 N 0.12 to 0.2

32 1200

1) According to GRÄFEN i.a. all potentials referred to the standard Hildebrand electrode 2) Designation in practice 3) Assumed value 4) German designation 5) Do not use V2A in the sewer atmosphere

Pitting does not depend only on the chloride content but also on other factors given below in abbreviated form:

− Material quality: the effective sum W in mass % chromium * 3.3 mass % molybdenum (Column i in Table 4) is relevant. The larger W is, the more positive is the pitting poten-tial UL (Column j of Table 4), i.e. the smaller the danger of pitting is (GRÄFEN et al.). In the Table the steel with the Material Number 1.4439 is used as example for a steel with high W value.

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− Redox potential URedox: if URedox is more positive than UL, which is the case, for example, with the addition or influx of oxidation means such as atmospheric oxygen, ozone, Fe3+ ions etc., pitting occurs - even with relatively low chloride contents.

− The greater the flow rate of the wastewater the more positive is UL, i.e. the smaller is the danger of pitting.

− With sensitising (see below), the susceptibility against pitting increases.

The factors listed show that no generally valid details for chloride concentrations, with which no crevice corrosion occurs, can be given. Analogous details in literature must therefore be considered very critically.

Crevice corrosion occurs only in wastewater containing chlorides, whereby crevices (some 0.1 to 0.5 mm width) between steels and non-conductors (e.g. plastics) are particu-larly dangerous points of occurrence. Crevice corrosion is dependent on the potential USP, which is usually more negative than the pitting potential UL, which underlines the danger-ousness of crevice corrosion.

The possibility of intercrystalline corrosion as a result of a heat treatment of stainless steels, for example with welding, must be considered. This is a selective type of corrosion with which the depositing of chromium rich carbides occurs at the grain boundaries. The corrosion resistance can reduce so far through the chrome depletion that grain disintegra-tion occurs. This material change is designated as sensitising (DIN 50 930, Part 4, 1993). Stabilisation against this type of corrosion can be achieved using the lowest possible car-bon content, which is, for example the case with steel of Material Number 1.4435 (see Ta-ble 4). Another possibility lies in the addition by alloying of titanium or niobium/tantalum, which have a high affinity to carbon and thus avoid the formation of chrome carbides (steel Material Number 1.4571).

The welding of stainless steels requires particular care and specialist knowledge (STRASSBURGER, 1976). Here attention should be drawn to some important points:

− selection of a procedure which avoids the access of atmospheric oxygen such as, for example, metal arc welding, inert gas shielded arc welding and submerged arc welding;

− deliberate, not too high addition of heat; − seam root covering; − taking account of increased contraction strains and thermal stresses.

With welding, oxide films and scale layers can appear, which prejudice the resistance against pitting. According to the draft DIN 50 930, Part 4, (1990), thin oxide films of a straw yellow colour can remain on the surface without prejudicing the corrosion resistance. All other oxide films must be removed either through shot peening using glass beads, through careful grinding (grain size > 100) or, best, through pickling. In the factory complete com-ponents are pickled in nitric acid - hydroflouric pickling baths, while pickling pastes, which are to be removed completely after treatment, are used on the construction site.

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With wastewater systems a mixed construction of different materials cannot be completely avoided. Contact corrosion can occur with metal conductive connections (direct electron conductive contact) of stainless steels with electro-chemical base materials, e.g. unalloyed steels (DIN 50 919, 1984). Particularly endangered are small area components made from unalloyed steel (anodes) connected to large areas made from stainless steel (cathodes). With protective measures against contact corrosion consideration must be given that coat-ings must be applied to the stainless steel to reduce the cathode area. Coatings on unal-loyed steel hide the danger that high anodic disintegration of non-alloyed steel occurs at often unavoidable, small faults in the coatings.

In summary the most important aspects, which should be observed with the employment of highly alloyed stainless steels, are listed below:

− use of stabilised steels if welded seams are planned; − professional weld seams and removal of oxide films; − crevice-free construction and processing, crevices > 0.5 mm are non-critical; − with the employment of bolted constructions gaps between components are unavoid-

able, therefore welded construction is to be preferred; − use of chloride-free sealants; − metallic bright surfaces; the formation of solid deposits is to be avoided; − the three-phase boundary air/steel/water can be endangered if solid deposits form in

which chlorides can accumulate; − a heavily anaerobic sewer atmosphere can lead to pitting even with stainless steels.

3.4 Plastics (PVC-U, PE-HD, PP, GFRP) 3.4.1 Preamble

Plastics are employed in the area of sewers both as load bearing pipe and shaft compo-nent materials as well as for corrosion resistant linings and coatings for concrete and cast iron pipes.

In the area of the overall sewer system plastics are also extensively used, for example in relining processes through the insertion of plastic pipes into damaged sewer systems and also in the form of subsequent application of linings.

Against the wastewater compositions which are permitted and occur in communal and other public drains the pipe materials given in Sect. 3.4.2 are generally to be seen as chemically resistant. The appropriate standard specifications for material quality and mate-rial properties are to be observed with the selection of material and tendering.

Both the external effects from chemical and static loading as well as various material properties are to be taken into account with the selection of the plastic for the respective application case. With coatings and linings, it must be further checked whether the specific parameters for the plastic processing can be maintained on the construction site and/or in the factory. The decision on the final material selection should be made dependent on this.

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3.4.2 Pipe Materials

Plastics are divided into thermoplastics: e.g. polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polyamide (PA) - thermosetting plastics (resins): e.g. epoxide resin (EP), polyester resin (UP), phenolic resin (PF) - and elastomers: e.g. synthetic rubbers, polyurethane (PUR). Thermoplastics can be plastically worked, baked or welded with high temperatures. Once manufactured, thermosetting plastics cannot be worked further. They can, however, be processed using machine procedures (milling, cutting, drilling) and joined with adhesives. Elastomers can no longer be thermally worked following chemical cross linkage. They can, however, be processed mechanically and glued.

For application in sewers, plastic pipes and fittings as well as plastic shaft components and linings, mainly from the following materials, can be employed:

Symbols

− polyvinyl chloride PVC

− high density polyethylene PE-HD

− polypropylene PP

− glass fibre reinforced plastics (GFRP) on the basis of unsaturated polyester resins UP-GF

With the employment of the above named polymer materials in sewers, the following DIN Standard Specifications are to be observed with regard to the requirements and quality assurances:

PVC-U DIN 19 534 PE-HD DIN 19 537 PP DIN 8077, 8078

In addition, for pipes with profiled walls made from thermoplastic materials, DIN 16 961 is to be observed and the initial, in draft, standard specification DIN 19 566.

DIN 19 565 applies for the employment in sewers of centrifugally formed pipes and fittings made from glass fibre reinforced unsaturated polyester resins.

Furthermore, a series of pipes, shaft components and linings made from plastic are used, for which currently there are no application standard specifications, but nevertheless carry the RAL Quality Mark of the "Gütegemeinschaft Kunststoffrohre (GKR)" [German Quality Organisation for Plastic Pipes]:

nonascendable lower shaft components R 7.1.23 R 7.4.20 R 7.6.8

profiled sewer pipes and fittings made from PVC-U R 7.1.12

R 7.1.19 sewer pipes and fittings made from modified PVC-U R 7.1.15

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sewer pipe lining components made from PVC HI R 7.1.13 driven pipes and fittings made from PVC-U R 7.1.16 sewer pipes and fittings made from wound UP-GF R 7.8.24

For employment in the area of private properties the components must correspond with the Technical Rules published in the "List of Construction Rules A" (Bauregelliste A) of the German Institute for Construction Engineering (DIBt) or the manufacturer must posses a "General Construction Supervision Authorisation" or a "Test Certificate" from the DIBt.

With the employment of pipe materials and the therefrom produced pipes, fittings, shaft assemblies, and pipe lining components in accordance with the above given standard specifications and directives, a sufficient chemical resistance for the normal service life of sewers in the communal area (wastewater in accordance with ATV Standard ATV-A 115, October 1994) can be assumed. The selection of the plastics is based on the specific load-ings.

Plastics are often employed for special applications, e.g. with the discharge of aggressive industrial wastewater or for product pipelines in chemical operations. With aggressive me-dia the directions and corresponding resistance tables of the supplementary notes to the basic standard specifications of pipes made from PVC-C, PE-HD and PP must be ob-served and the details given by the pipe manufacturer are to be taken into account (DIN 8061, Suppl. 1, DIN 8075, Suppl. 1, DIN 8078, Suppl. 1).

With pressure pipelines both DIN Standard Specifications (DIN 8061/62, DIN 8074/75, DIN 8077/78) and the Standards of the German Association for Welding Technology (DVS Standard 2205, Part 1) are to be observed for permitted loading.

As with inorganic or metallic materials, plastics can be attacked not only from the surface but also from inside as small molecules can diffuse internally. Primarily organic solvents and also other low-molecular, gaseous and fluid substances can diffuse into plastics. Through this, with some plastics (see above-named supplements), a swelling and subse-quent softening can occur. In particular, thermoplastics and soft rubbers can be attacked, also from inside, through internally diffused substances, while duroplastics and hard rub-bers are attacked mainly from the surface (SGK, 1994). With PVC the stabilisers can also be attacked under anaerobic conditions (e.g. in anaerobic tanks).

Local, mechanical damage can also be caused to GFRP pipes through incorrect handling during delivery (sudden loading) and in operation (incorrectly operated high pressure cleaning). At the damage sites the medium can penetrate into the bearing layers through micro-cracks in the gel coat and, depending on the structure, also into the bearing layers along the fibres due to capillary forces (when employing long fibres). Through this the bearing capacity can be reduced. Damage to the surface and faces are to be mended us-ing resin in order to avoid a penetration of the medium through capillary forces.

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3.5 Sealing Materials 3.5.1 General Requirements on Sealing Materials for Wastewater Systems

Sealing materials, which have contact with aggressive water, soil or gas, must be so manufactured or protected that they can resist their attacks without prejudice to their func-tional capability.

Accordingly the functional capability of pipe connections must be ensured with influences from

− wastewater with pH values of 2 to 12, − commercial wastewater in accordance with ATV Standard ATV-A 115.

As far as wastewater (e.g. before a separator/interceptor) occurs with properties deviating from these, the respectively relevant loadings are to be taken into account. In water protection areas the functional capability of the pipe connection must be additionally en-sured for five hour effects of heating oil EL and motor fuel No. 2 in accordance with DIN 53 521. Insofar as, in individual cases (in particular in the area of private property drainage sys-tems), one has to reckon with longer-term effects of these substances, appropriately resis-tant sealing materials are necessary.

With light liquids, for sewers, at least on the flow path up to the low density material sepa-rator, sealing materials with a separate resistance verification are to be employed in ac-cordance with the German Institute for Construction Engineering, Berlin, "Construction and Test Principles for Seals made from Elastomers with Increased Resistance Capability against Light Fluids for Pipe Connections in Wastewater Systems".

3.5.2 Materials for and Properties of Sealing Materials

For sewers and drains almost exclusively the following come into consideration:

− sealants made from elastomers in accordance with DIN EN 861, DIN 4060;

− sealants on the basis of polypropylene and polyurethane for vitrified clay pipes in accor-dance with EN 295;

− two component sealing compounds on the basis of polyurethane for internal pipe thrust seals in man accessible sewers and pipelines produced by pipe driving;

− cold worked plastic sealing compounds in accordance with DIN 4062 are used only in individual cases.

With regard to chemical effects all sealing materials meet the requirements of DIN 4062. The functional capability of the pipe connection remains assured with the effect of waste-water with pH values between 2 and 12 and with commercial wastewater with guidance values in accordance with ATV Standard ATV-A 115 (including the limiting values for sub-stances in accordance with the Indirect Discharger Ordinance of the Federal (German) States.

As far as light liquids (hydrocarbons such as benzine (petrol), heating oil and similar) or volatile chlorinated hydrocarbons (CHCs) are discharged temporarily into the public sew-erage system as a result of an accident, these should cause no disadvantageous effects on the sealing function of the sealants.

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Microbiological attacks on sealants in accordance with DIN 4060 and DIN EN 295 have up until now not be determined with sewers. Biologically conditioned material defects occur only with two component sealants on the basis of polysulphide rubber (Thiokol = US brandname), which are therefore considered as unsuitable for wastewater systems.

For the area of the public sewerage system negative effects on sealants due to chlorinated hydrocarbons (CHCs) are not to be feared. Apart from the fact that CHCs have only a rela-tively slight water solubility, they belong to the water hazarding substances which, accord-ing to legal regulations, may only be discharged in quantities which are completely harm-less for sealants.

4 Corrosion Protection

4.1 Compound Materials and Linings

They are produced mainly from PE, PVC (free of plasticiser) and UP-GF and have, de-pending on formulation, a good to very good resistance against acids, alkaline solutions, fuels and oils. Further information can be taken from ATV Advisory Leaflet ATV-M 143.

4.1.1 Pipe Linings with New Constructions

Parallel to the testing of various lining systems there are years of experience available with pipe linings made from plastic widths. They are produced mainly from PE, PVC (free of plasticiser) and UP-GF and have, depending on formulation, a good to very good resis-tance against acids, alkaline solutions, fuels and oils.

4.1.1.1 Factory Produced Pipe Lining Using PVC Plasticised Films

In the eighties internal linings using 2-3 mm thick PVC plasticised films were installed which were anchored in the concrete using ribs. With these, films produced in the USA and in Germany a release of the external water overpressure from the groundwater due to encasing with concrete, is only possible at the upper 300° or at 360° through drainage holes below the water level.

The films were installed with success; they had only the disadvantage that they were not stable enough against the cleaning equipment used with later operation.

The pipes were so manufactured in the concrete factory that, at the pipe faces, the films overlapped or were flush to each other. In both cases the connection, after laying the pipes, had to be welded on site in order to receive a continuous corrosion protection.

Currently the factory produced lining with plastic film is no longer practised in Germany.

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4.1.1.2 Factory Produced Pipe Linings Using Unplasticised PVC Web Sheets

A further, very widely used, solution for pipe lining is provided by lining using PVC hard helical films. The 2 or 3 mm thick PVC hard profile sections are anchored to the concrete using ribs and, with a 360° encasement in concrete, accept the full external water pressure from the groundwater and the diffusion pressure.

The sealing of the pipe joints takes place through an external seal by means of a rubber seal and an internal permanently elastic seal on a polyurethane basis which, at the same time, ensures continuous corrosion protection.

Due to the cases of damage which occur on the internal permanently elastic seal, precise information on the actual chemical attack, for example as a result of biogenic sulphuric acid, is necessary with regard to the sealing material used.

The compatibility of the sealing material with PVC hard sheets is also to be investigated (possible plasticiser migration). Due to negative experience with which the sealing material softens due to biogenic sulphuric acid, joint closure using laminated GFRP is practised in several towns. With this, however, often adhesion problems and also detachment are ob-served. The cause of the black discoloration of PVC web sheets, determined in many places over recent years, is still not known.

4.1.1.3 Factory Produced Pipe Lining Using Web or Knob HDPE Sheets

In the meantime, due to modern manufacturing processes, several lining systems using PE-HD films with a full-surface overlay anchorage made from webs or knobs. The material thickness (without anchorage system) is 4 - 5 mm.

Pipe connection is by means of overlay welding of the pipe joints, in part with the aid of a joint band. To ensure an even welding seam quality, extrusion welding, if possible using control, is to be preferred.

As the good welding capability and the corrosion resistance of the material is decisive for the durability of the overall system, precise specifications with regard to the material re-quirements are required. As an aid the requirements, which already exist for dump/landfill linings, can be enlisted.

Aim of these requirements which, for example, are laid down in the BAM (German Federal Office Office for [Chemical and mechanical] Materials) Authorisation Directive for PE-HD, is to ensure the suitable material selection, the manufacture and the installation of a func-tioning and long-term resistant corrosion protection element within the framework of a quality assured production in accordance with DIN ISO 9000.

If water pressure on the reverse side of the linings is to be expected, the lining system should, to avoid long-term deformation, be eased by means of stress relieving drillings in the base.

4.1.1.4 Factory Produced Pipe Lining Using Vitrified Clay Shells (Ceramic Plates)

Vitrified clay shells and sole plates are a possibility for corrosion resistant lining of pipes, whereby corrosion resistant mortars are to be used.

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4.1.1.5 Retrofitted Pipe Lining Using Plastic Sheets

A further development with large calibre main sewers has been the installation at the con-struction site of an internal lining made from PVC hard sheets or from PP sheets of 6 to 8 mm thickness, after laying the pipes. These sheets were subsequently stretched axially in one piece over 300° in the sewer and held at the bottom by rails using pins made from stainless steel. The relief of the water pressure behind the sheets is achieved via openings in the foot rails. The sheets are self-supporting but are not dimensioned for additional static loading. The ends of the sheets are welded together. This solution has proved itself against biogenic sulphuric acid attack in routine wastewater operation.

Due to the unlined base, however, other solutions are to be preferred for aggressive wastewater. Due to the small inherent stability of the above mentioned thermoplastics, to-gether with a missing full-surface anchorage in the pipe concrete, however, it is to be noted that, with extreme operational conditions (surge flushing, reflected waves in front of closed gate valves) damage has already occurred on linings, which made an additional subsequent attachment necessary.

A retrofitted lining using plastic sheets is currently no longer employed in Germany.

4.1.2 Shaft Linings with New Constructions

4.1.2.1 Factory Produced Shaft Lining Using Plastic Sheets

Similar to pipe lining, the employment of full-surface widths of back-anchored plastic is also possible with shaft linings. With the design and also the construction of such systems, however, there are specific parameters to be taken into account. Thus, with PVC hard web sheets, particular attention is to be given to the joint problem. With PE-HD sheets, with reverse side water pressure, the drainage to the bottom must not be hindered by the ar-rangement of the anchorage elements.

The employment of the above named widths of plastic sheet with shafts with numerous fittings, recesses, outlets or sharp angled inlets is not economical and is problematic for absolutely watertight concrete protection. These design elements result in numerous ir-regularly formed surfaces. Thus there arises a large number of profile pieces to be cut on site and numerous joints between the individual pieces, which are difficult to close. In such cases the solutions in accordance with Sect. 4.1.2.2 are more practical.

4.1.2.2 Shaft Lining Using GFRP Sheets and Elements

A further possibility for shaft lining lies in a retrofitted GFRP lining. Here, prefabricated GFRP sheets made from polyester resin and glass fibres, with a thickness of 2 mm, is fixed to the concrete using plastic pegs. Subsequently there is a full surface, two-layer GFRP laminate over the whole surface through which all joints and peg heads are cov-ered. Finally there is a double topcoat of the same polyester resin. With the last topcoat a 5 % paraffin solution is added in order to achieve a adhesive-free and saponification resis-tant hardening. The total layer thickness of such a polyester resin lining is 5 mm, its aver-age glass content is 20 - 25 %. In order to ensure a full surface bonding of the on-site ap-plied laminate with the prefabricated sheets, the prefabrication of the sheets should not take place too soon before installation (max. 3 to 6 months according to manufacturer's specifications).

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The lining should not be dimensioned on water pressure. More important, groundwater which has appeared in the natural spaces between GFRP and concrete is to be drained off and allowed to exit at the bottom. Artificially enlarged spaces have not proved themselves. For better quality control one should avoid the addition of colour pigments into the polyes-ter resin. Attention is to be paid to a careful selection of the resin and glass qualities em-ployed. Resin qualities with moulding properties in accordance with DIN 16 946, at least Type 1130, and corrosion resistant ECR glass in accordance with DIN 61 855 are recom-mended.

With smaller shaft dimensions with regular geometry, a solution using prefabricated GFRP elements is possible. These elements consist of glass fibres and polyester resin whereby, to increase the stiffness, quartz sand is added. The composition of the individual compo-nents varies here depending on manufacturing process. The manufacture takes place us-ing the wound or centrifugal procedure.

The static dimensioning of the elements takes place either for the full loads or only for the acceptance of the water pressure. In the latter case an outer concrete shell is necessary.

4.1.2.3 Shaft Lining Using Sewer Bricks

In some areas of sewerage systems shaft structures are carried out using sewer bricks. In order here to avoid sulphuric acid corrosion to the cement bonded mortar joints, the joints are dug out to a depth of ca. 2 cm and filled with an epoxy resin mortar.

4.1.3 Pipe Linings with Renovation

With the renovation of pipes one must fundamentally differentiate between accessible and non-accessible profile sections. The problem with all sewers in operation lies in the main-tenance of the runoff capability.

Insofar as a drying out using backing up is not possible, there remains only the solutions of pump-over of the wastewater or piping, which is carried out with sheets stretched over 300 ° in the bottom and, in other cases, laid above ground and operated as siphon pipelines.

To limit the terms used these are now defined whereby, in future, the normal international terms of DIN EN 752 should be used [already applied in this translation].

Table 5: Comparison of previously used and new standardised terms with the repair of sewers

Conceptual content ATV Advisory Leaflet ATV-M 143, Pt 1

DIN EN 752

Repair of locally limited damage Corrective maintenance Repair

Re-establishment of damaged sewers maintaining the basic material

Rehabilitation Renovation

Production of new sewers by giving up or destroying the basic material

Renewal Renewal

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4.1.3.1 Renovation of Non-Man Accessible Profile Sections

Depending on the parameters, various procedures are employed with non-accessible pro-file sections. Insofar as the acceptance of external loads can still be taken on by the origi-nal sewer, the insertion of inliners, which lie against the sewer walls, is suitable and is car-ried out without the production of an insertion trench. Equally suitable is the insertion of so-called inliners, made from PE-HD, or GFRP pipes. This solution, however, means a reduc-tion of the flow cross-section and requires an insertion trench.

The advantage of these solutions exists a) in the possibility of employing material specifi-cations which correspond with the actual requirements and, b) it is possible with these to pass external loads to the inliner by appropriate dimensioning which, with unsatisfactory load bearing sewer pipes, makes a possible renewal unnecessary. A static calculation for relining pipes (with buckling proof for plastic pipes) is necessary for installation and opera-tional conditions.

The annular space between the outside surface of the inliner and the inside of the old sewer is dammed up following reconnection of domestic connections.

With all the given solutions there is a problem with the reconnection of existing domestic connections with a technically sound corrosion safe sealing to the new inliner.

If this problem cannot be solved with the employment of appropriate robot equipment from outside the sewer, as a rule there remains only the reconnection in an open trench.

With a large number of domestic connections this can frustrate the economy of an inliner solution.

4.1.3.2 Renovation of Man-Accessible Profile Sections

With the renovation of man-accessible profile sections, the same solutions as are de-scribed under Sect. 4.1.2.1 are applicable. The reconnection of the lateral inlets is here very simple to solve from the sewer.

Further renovation possibilities exist with sewers that remain stable, for example with the installation of prefabricated plastic sheets, e.g. made from GFRP, which are stretched over 300° and pegged in the sewer. With this the closure of joints with the use of the same ma-terial as for the sheets, for example overlay laminates with GFRP and welding with ther-moplastics.

4.1.4 Shaft Linings with Renovation

With the renovation of operational shafts the lining as described in Sect. 4.1.2.2 is used.

Due to the essentially better access of a shaft as compared with the sewer, it is neverthe-less a question of economics whether it is also possible to carry out a renovation on the basis of plastic modified cement mortar and possibly to repeat this renovation over a pe-riod of operating time.

The employment of pure plastic mortar is very problematic due to the parameters (water exercising pressure, wet surfaces).

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4.2 Protective Paints and Coatings

The essential part with protective paints and coatings is the pre-treatment and priming. Information on this is contained in ATV Advisory Leaflet ATV-M 263.

One surface protective layer produced from one or more associated layers counts as a coating. A coating serves to hinder extensively the penetration of liquid or gaseous sub-stances into the concrete. Such coatings consist, as a rule of reaction or thermosetting resins.

Coatings are particularly endangered through diffusion into or through the coating by small molecules (water, oxygen), which leads to corrosion under the coating and to the formation of blisters. Particularly endangered are the coatings under thermo-diffusion conditions (KLOPFER, 1974), e.g. cold pipe walls, warm attacking medium which, with pipelines in groundwater, as really always the case.

Due to the temperature gradients in the coatings connected with this, a gradient for the partial pressure of the water vapour also occurs so that the water molecules are pressed through the coating by the pressure difference. With metallic materials, in particular steel, occurs under the coating. Cement bonded mortars corrode, in general first if the coating has broken and the corrosive medium reaches the unprotected material.

Blisters can also occur due to osmotic processes if, for example, water soluble sub-stances, such as solvents from the coating or water soluble salts are present due to faulty pre-treatment of the surfaces between coating and material. Therefore solvent-free coat-ings only are to be always used on absolutely clean surfaces.

4.2.1 Coatings on Iron Materials

Coatings on iron materials on the basis of epoxy resin or polyurethane, which are applied in the factory under clearly defined parameters, as a rule have good resistance.

The problem of such coatings consists of the danger of damage (subsurface rusting) and the therefrom resultant poor chance of repair of the system in running operations.

Here, in many cases, there remains only the complete dismantling of the unit and a new coating. Preferred are therefore designs made from corrosion resistant material, e.g. stainless steel.

4.2.2 Coatings on Concrete Surfaces

In general concrete surfaces in sewers do not require to be coated. If the concrete in sew-ers is to be coated then surface protective systems (SPS) in accordance with the DAfStb (German Service Instruction For Registrars and their Supervisory Authorities) Directive for Protection and Repair of Concrete Components (8/90) are to be applied. The Directive gives information on coating substances, requirements on the substance and on the con-crete surface.

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Through the moisture effects on both sides in the concrete with underground sewers, the adhesion of the coating on the surface, and with this the durability of the protection is jeopardised. In addition the adhesive ability can, from the very beginning, be prejudiced as a result of moisture in the concrete. The technical problems which result due to this mois-ture influence are currently not completely solved. Therefore, in general, the subsequent application of a coating with a sewer which has been buried fir a long time must be con-sidered to be more problematic, both with regard to implementation as well as with regard to durability, than a coating which is applied before laying the pipe.

Even factory applied coatings often have weak points already after short operating times. To these count, for example, the formation of blisters, which before long always lead to rupture of the coating. Following rupture the pipe material is wide open to the corrosive attack. With biogenic sulphuric acid corrosion, the corrosion can even develop much more intensively under the ruptured blister. Therefore attention is to be paid that coatings with substances containing solvents, as a rule are not sealed against diffusion or against os-mosis, so that, for example, as a result of SO4

2- diffusion, a formation of ettringite under the coating can occur. Particular attention must also be paid to edges, for example at pipe faces, as here the coating can frequently be heavily applied or the coating is damaged dur-ing installation

5 Notes for Planning and Operation

5.1 Notes on Planning

5.1.1. Preamble

Corrosion problems can be extensively avoided already with the planning of wastewater systems by observation of the following information. Planning measures are particularly suitable for the hindering of biogenic sulphuric acid corrosion. If, despite all planning pre-cautions, corrosive conditions cannot be excluded then a material resistant against corro-sion is to be selected or non-corrosion resistant material are to be protected.

5.1.2 Location of Wastewater Treatment Systems

With the planning of central wastewater treatment plants, from the aspect of the sulphide problem, catchment area and location are to be so determined that the wastewater reaches the wastewater treatment plant from the source over the shortest distance and in the quickest possible time. With increasing length of collectors and/or increasing flow times and the operation of pressure pipelines the danger of sulphide problems increases.

5.1.3 Composition of Wastewater

Insofar as wastewater is available at the time of planning, so that its properties can be in-cluded in the planned conditions, several wastewater analyses are to be carried out and the analytical results attached to the request for tenders for the pipes. As parameters the following, for example can be considered: temperature, pH value, settlable solids, Chemi-cal Oxygen Demand (COD), magnesium, ammonium, sulphate, sulphide. The pipe sup-plier is to take on the guaranty for the satisfactory corrosion resistance for the so-described wastewater composition.

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5.1.4 Indirect Discharger Operations

The indirect dischargers recorded in a catchment area are to be assessed with regard to the discharge of possible corrosively acting wastewater. Experience shows that one has to reckon with the exceeding of the concentration ranges laid down in the communal drain-age bylaws.

A listing of commercial and industrial branches with possible corrosive wastewaters and their boundary values is contained in ATV Standard ATV-A 115. In addition those opera-tions are to be particularly observed which discharge organic acids with their wastewater; with cement bonded materials heavy acid corrosion from such wastewater can be caused already with p<H values slightly below 6.0. The connecting sewer is to be made from acid resistant pipes. Materials with sufficient corrosion resistance are to be provisioned for road sewers, until a sufficient dilution has been achieved.

Through the discharge of acidic wastewater there is not only the danger of an acid corro-sion in the bottom of the street sewer but also, with wastewaters containing sulphides there is also the possibility of transferring the whole of the sulphide from the ionogenic form into the undissolved (molecular) form as hydrogen sulphide. Already with a pH value of 6.0, the sulphide exists is almost completely as hydrogen sulphide, which emits from the wastewater into the sewer gas space as volatile hydrogen sulphide gas and, as a result, can lead to biogenic sulphuric acid corrosion.

5.1.5 Drainage Procedures

Precipitation events cause a flushing and dilution of aggressive wastewaters in combined wastewater sewers. With slight partial filling, depositing of solids can extensively in com-bined systems so far as the dry weather channel is not developed.

In comparison with combined sewers, normal sewers have a higher partial filling with dry weather so that, through higher flow rates and bottom drag tension less deposits can form as a source for biogenic sulphuric acid corrosion.

5.1.6 Gravity Pipelines

Pipe profile:

In comparison with circular profiles, oval profiles are to be preferred with regard to a re-duced danger of bottom deposit formation. In combined sewers oval profiles have a some 20 % higher bottom drag tension than circular profiles.

External corrosion:

At the planning stage investigations into the soil and groundwater aggressiveness with as-sessment in accordance with DIN 4030 03 DIN 50 929, Pt 3, are to be carried out before laying down the pipe material. The same applies for shafts and other structures.

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Flow rate:

The flow rate should always lie above the critical velocity at which depositing of solids oc-curs (critical gradient for deposit-free operation see ATV Standard ATV-A 110, Table 12). Verification of flow rates are also to be carried out for discharge conditions at night-time and areas of back-up of reductions in cross-section, siphons, etc. If the necessary flow rates for a deposit-free operation cannot be maintained due to the topographical condi-tions, the employment of particularly corrosion protected pipes is recommended. In addi-tion measures can be taken in sewer operation (see Sect. 5.3.1).

With the assessment criteria, in addition to annual costs corrosion measures, odour loads and the safety of operating personnel are also to be assessed.

With regard to sewer cross-sections the employment of non-circular pipes and the ar-rangement of parallel pipelines should be considered. In collectors with large diameters channels with small cross-sections can be used before for initial operational periods. With trunk sewers, in particular with the joining of two collectors, a grit chamber should be con-sidered.

Natural ventilation:

The ventilation of sewers improves the desired aerobic condition in the wastewater. Venti-lation takes place through manhole covers, road gullies and via the roof of extended drop pipes (ventilation pipelines) in houses. In addition, ventilation pipelines at provisional ends to a sewer, at intervals of ca. 25 m between shafts with man-accessible sewer sections, at the start and end of a curved sewer, with connection structures, at the high point of cas-cades, at gate valve installations, etc. are recommended. Ventilation points can be so de-signed that an adapter is installed in the crown of the pipeline, from which a vertical venti-lation pipeline of DN 300 can be led up to the surface of the road, terminating with cover box, covering and natural ventilation.

Drop structures:

With favourable terrain conditions, drop structures are to be preferred due to the consid-erably better oxygen supply in normal gradients. However, with wastewaters containing sulphides one should avoid bed drops due to stripping effects, unless special precautions are taken and odour problems are not to be expected.

Fundamentally turbulence with wastewater loaded with sulphides is to be avoided. With branches the velocity gradient is to be kept as small as possible. The delivery of wastewa-ter from laterals into lower main collectors should continue to flow, without dropping; for this appropriate drop structures (e.g. bypass for small flows, chutes, vortex drop shafts, elevator siphons, possibly gate valve regulation) with energy conversion possibilities (e.g. in corrosion protected whirlpool basins) are to be preferred. Measures for corrosion protec-tion and for the treatment of exhaust gas are to be given particular attention. Pipe sockets planned for latter connection are to closed off water tight in order that no wastewater can occur in them.

Shut-off devices:

Openings for flushing and shut-off devices for pipeline flushing are recommended, at least with larger pipe diameters. Shut-off devices are also useful for regulation of run-off, for clo-sure in emergencies and during work in the network.

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5.1.7 Pump Stations and Cross-sectionally Filled Pipelines

Pump sumps:

The development of pump sumps of pump stations (vacuum space) has an influence on wastewater freshness. Sulphide-free wastewater should drop into the pump sump from the inlet sewer, so that the take-up of oxygen is improved. With wastewater containing sul-phides exhalation can be reduced if the inlet joins below the pump shut-off level. The pump sump should be emptied at short intervals, as far as possible completely, so that sewer film on the walls and floor are at least partially aerated. Optimum solution is a large wastewater surface for oxygen transfer with a minimum of sewer film surfaces. The con-tinuous movement in the pump sump or self-cleaning bottom gradient (at least 60 % incli-nation of slope) extensively prevent depositing of solids. See also ATV Standard ATV-A 134).

Selection of cross-section:

Several short consecutive pressure pipelines cause higher annual costs than a long pres-sure pipeline with only one pump station, but can prevent sulphide problems. With large discharge variations, e.g. with combined systems, a pipeline with small diameter should be laid for sewage and a further pipeline with larger diameter should be laid for combined wastewater. In order that the wastewater in the combined wastewater pressure pipeline, with occasional several week long dry periods, does not degrade, this pipeline should empty automatically into the outlet or pump sump with favourable terrain conditions follow-ing completion of delivery. For this the pipeline is to be laid with continuous gradient. In siphons a deposit-free operation is often possible only through the selection of two or more adjacent cross-sections matched to the variations of the amount of the wastewater pro-duced or through the implementation as air cushion siphon.

Flow times:

Pressure pipelines and, if required, siphons, are potential sources for sulphide problems due to a lack of wastewater aeration. So far as they are unavoidable they should be kept as short as possible so that even with night-time flows a flow time of some two hours is not exceeded; otherwise corrosion protective measures and, if necessary, measures for odour reduction are to be provided in the lower subsequent gravity sewers.

Flow rates:

Deposits in pressure pipelines favour the clogging of the pipeline and represent a consid-erable source for biogenic sulphuric acid. To prevent deposits in larger pressure pipelines, flow rates of at least 0.5 m/s, otherwise of at least 1.0 m/s during the delivery phase are to be maintained. With a smaller daily total delivery time or with very long standing periods, an even higher flow rate must be selected as lower limit. By the selection of appropriate flow rates with wall shear stresses of at least 3.8 N/m2 with daily peak flows, keeps the sewer film in pressure pipelines very thin, so that their contribution to sulphide formation is heavily reduced (THISTLETHWAYTE, 1979).

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Outlet:

The transfer area at the end of the pressure pipeline deserves a particularly careful design. The cross-section of the outlet of the pressure pipeline should stand completely filled even during pump resting times in order that corrosion cannot occur in the pipe crown of the pressure pipeline (crown height of the pressure pipeline = sole height of the subsequent sewer). Turbulence is to be extensively avoided by appropriate channel design in the outlet shaft.

Prognosis for sulphide formation:

Although it has not been possible to achieve good accuracy for a prognosis of the rate of sulphide formation and/or the attack and destruction rates on cement bonded materials with biogenic sulphuric acid corrosion using the well-known computer models (ATV Stan-dard ATV-A 116; BIELECKI UND SCHRAMMER, 1987; HVITVED-JACOBSEN et al., 1988; POMEROY, 1976; THISTLETHWAYTE, 1979; US EPA, 1985), these models still offer the possibility for estimating the corrosion danger due to biogenic sulphuric acid cor-rosion.

Maintaining wastewater freshness:

To maintain the wastewater fresh, air can be coarsely bubbled into the vacuum chamber; it can be prevented, through suitable design, that gas bubbles reach the pump suction area. With an artificial aeration air extraction system with off-gas treatment, already determined sulphide can be removed from the airspace of the suction chamber. With the employment of spiral pumps there is an additional oxygen input in the spiral.

Aerobic pressure pipeline operation:

The oxygen dissolved in the wastewater is depleted in the pressure pipeline by the micro-organisms in the sewer film, wastewater and, possibly, in the deposits. The daily oxygen consumption OV can be estimated in accordance with (LOHSE, 1987)

OV = 0.024[π . D . L(ZSh + d . ZAbw/4) - Q24 . cO2] with OV [kg/d] oxygen consumption in the pressure pipeline D [m] pipe internal diameter L [m] length of the pressure pipeline ZSh [g/(m2 . h)] oxygen depletion in the sewer film; can be determined using depletion measurements ZAbw [g/(m2 . h)] oxygen depletion in the wastewater; can be determined using depletion measurements; mainly at 20° C: - for 2 hours old wastewater 7 g/(m3 . h)] - for 10 hours old wastewater 15 g/(m3 . h)] - for 20 hours old wastewater 17 g/(m3 . h)] Q24 [m3/h] delivery flow, determined over 24 hours cO2 [mg/l] oxygen content in the wastewater at the start of the pipeline

If, for security, a remaining oxygen concentration of 1 mg/l is sought in the outlet area of the pressure pipeline, the following quantity of oxygen OC [kg/d] is to be stored in the pressure pipeline. From experience no safety allowance is required for this in order largely to prevent desulphuration.

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OC = 0.024[π . D . L(ZSh + d . ZAbw/4) - Q24(cO2 - 1)]

To avoid an anoxic milieu in the pressure pipeline, there is the dosing of compressed air, bulk oxygen, nitrate or hydrogen peroxide. An alternative to delivery using hydraulic units is pneumatic delivery. Insofar as too long anoxic retention times occur only at night-time, subsequent blowing of compressed air is sufficient.

By creating an aerobic milieu in the pressure pipeline not only are corrosion problems kept under control but also other possible sulphide problems (odour emissions, safety hazards for operational personnel, bulking sludge in the biological treatment stage) are prevented or reduced. Attention is to be paid that, with concurrent injection of compressed air or bulk oxygen, biogenic sulphuric acid corrosion can occur with cement bonded pipe materials (e.g. fibre cement and cement mortar clad cast iron) in gas bubble filled pipe crown areas.

Fittings:

In pressure pipelines, which only run empty over partial stretches, aeration and air removal points are to be installed at the high points (problematic due to the wastewater content substances), at low points drainage devices, and possibly also cut-off facilities. Already with planning the possibilities of chemical dosing and/or gas injection should be planned as a prophylactic measure. With this, additional pressure losses due to gas pockets are to be taken into account in the calculation.

Pressure pipeline gradient:

Gases such as air and pure oxygen can be dosed simply into continuously rising pressure pipelines. Wastewater can be forced out of gently sloped pressure pipelines using com-pressed air; however, a part of the wastewater remains at low points.

Flushing:

With longer pressure pipelines a facility for extraction of water from a receiving water or for groundwater can be provisioned so that the possibility of carrying out flushing in operation exists.

Pressure and vacuum drainage:

Pressure drainage systems are employed in areas which are difficult to drain (wide spread housing), high groundwater levels, slight terrain gradients). In such systems time regu-lated flushing facilities using water or compressed air are used for the limitation of desul-phuration. Vacuum drainage is, in comparison with pressure drainage, less problematic with regard to corrosion susceptibility. See also ATV Standard ATV-A 116).

5.1.8 Soil and Groundwater Conditions

It is to be determined in the planning stage whether the pipelines or structures lie in the groundwater zone; if this applies an investigation of the soil and groundwater for their ag-gressiveness, against cement bonded materials, in accordance with DIN 4030 and, against iron materials, in accordance with DIN 50 929, Pt 3 should always be carried out.

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5.2 Addition of Chemicals

5.2.1 Fundamentally Suitable Means

The addition of chemicals can, already with planning, be taken into account or can also be provisioned for later problems in pipe operation. The effects on the limiting values of treated wastewater and the sewage sludge are to be taken into account.

Through the addition of various chemicals the following is possible:

− avoidance of desulphuration conditions in the pressure pipelines and other cross-sectionally filled pipelines (using air, pure oxygen, nitrate, hydrogen peroxide);

− oxidation of already formed sulphides in pressure and in gravity pipelines (using hydro-gen peroxide or ozone);

− precipitation of sulphides in gravity pipelines (using iron and other metal salts);

− prevention of the appearance of molecular hydrogen sulphide from the wastewater into the sewer atmosphere with gravity pipelines by alkalisation (using lime, sodium hydrox-ide solution).

With the employment of nitrates the buffer capacity of the wastewater is to be noted. The effective and economic use of chlorine and chlorine compounds is not practical, due to the increase of the AOX values in the wastewater. With sulphide precipitation using iron chlo-ride a precipitation sludge occurs, which tends heavily to the formation of deposits and can thus cause further problems. Other metals which also form compounds with sulphides such as lead, copper, zinc do not come into consideration due to the low limiting values for metals in wastewater and in sewage sludge. With the alkalisation of the wastewater to pH values above 9, the soluble sulphide appears as HS- ions, so that a gassing-off of hydro-gen sulphide is prevented. The procedure is, however, not practical in general, as the pH value is lowered through lower lying influents and biological procedures in the wastewater (formation of organic acids and of carbon dioxide) and, in addition, increased sludge pre-cipitation occurs.

The normal procedures are described below.

5.2.2 Addition of Compressed Air and Pneumatic delivery

To support aerobic conditions compressed air can be inserted into a pressure pipeline us-ing the following procedures:

− hydraulic delivery using addition of compressed air during pump operation;

− hydraulic delivery at intervals and air compression in the pumping pauses or several times a day ("air flushing");

− pneumatic delivery.

The oxygen contained in the air supports the aerobic milieu in the pressure pipeline. The gas bubbles prevent the formation of deposits. The retention time of the wastewater in the pressure pipeline is shortened.

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Although, with hydraulically operated pressure pipelines with interval operation, the pres-sure losses fall with the addition of compressed air during the pauses in pumping, they however, effect only a slight admixture in the wastewater. To be preferred is the addition of compressed air during the pump running times, whereby both the delivery performance of the pumps as well as the compressor are to be matched to the increased operating pres-sures. By using the highest operating pressure at the beginning of the pipeline with con-current delivery, an increased gas solubility is achieved. With a wastewater flow rate of at least 0.7 m/s the air input is supported by the increased turbulence.

Pressure pipelines with continuously increasing or no sole gradient in the delivery direction are particularly suitable for the procedure. With longer pressure pipelines, long drawn-out gas phases can form which, in the upper reaches of the pipe, spread out over the underly-ing wastewater. Here the placing of individual collection pockets, in which the wastewater collects in plugs, is recommended, so that the wastewater plugs are subsequently driven through the pipeline by the compressed air.

The necessary air requirement is dependent on numerous factors, for example from the composition of the wastewater and its temperature, retention time in the pump sump and in the pressure pipeline, pipeline geometry and the desired degree of sulphide control. One can assume a compressed air requirement of 1 m3 air per m3 of wastewater per hour; more accurate calculation bases are contained in Sect. 5.1.7. With compressed air flush-ing, in general it is not possible to empty the pipeline completely, which is also not neces-sary. On numerous occasions it has proved sufficient if, per flushing activity, a third to half the pressure pipeline volume is exchanged for compressed air.

Simple, hydraulically driven systems consist of an air compressor which, with smaller submersible motor-driven pumps, can be installed in the control box. In addition to direct compressed air injection into the pressure pipeline, the compressed air can be fed in via a compressor plant (e.g. sound insulated piston compressor) with or without compressed air chamber, which is also normal with pneumatic siphon system. Although compressors with low rotation speeds have a slightly lower efficiency, they have, however, less maintenance effort and faults. Connection of the compressed air pipeline to the wastewater pressure pipeline in general is by means of a simple adapter.

At the start of a ventilation the sewer film on the inner wall of the pressure pipeline is par-tially removed due to the turbulence and is removed as black sludge, which can take sev-eral days.

The procedures are particularly suitable with short pressure pipelines with small pipeline cross-sections as well as with low sulphide development rates. The investment and operating costs are relatively small. Compressed air requires no storage, is not corrosive, bactericide or hazardous to health.

With the procedures it is to be noted that only some 21 % of the inserted gases are avail-able as oxygen to support the milieu; the remaining part of the gas consists almost entirely of nitrogen. The gas which does not dissolve can occasionally lead to the formation of pressure surges, to cavitation effects on the pipe inner wall and to explosive-like escape at the end of the pressure pipeline.

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With fibre cement or cement centrifuged metal pipe pressure pipelines there is a possibility of biogenic sulphuric acid corrosion if, at the start of the pressure pipeline, sulphide is con-tained in the wastewater, there is a mixing of wastewater and gas in the course of the pipeline and, with this, extended air bubbles form stably over longer periods, particularly at high points without ventilation.

In many cases it has been possible to overcome sulphide problems by the addition of compressed air or by pneumatic delivery.

5.2.3 Addition of Pure Oxygen

Through the dosing of pure oxygen (O2), produced in bulk, a considerably higher solubility is effected so that, even with longer flow times in a pressure pipeline, for example with long pipelines or with small delivery flows in the night hours, aerobic conditions are main-tained. The solubility of the oxygen in the wastewater is directly proportional to the partial oxygen pressure in a gas mixture. With the employment of pure oxygen, in comparison with atmospheric oxygen, one requires to charge only ca. 1/5 of the gas quantity. The saturation concentration for pure oxygen in water at 20° C is some 125 mg/l at 2 bar pipe-line operational pressure, 210 mg/l at 4 bar and 300 mg/l at 6 bar. For wastewater, in ac-cordance with the oxygen transfer correction factor, lower values are to be applied over which, however, no precise information is available. One should assume an oxygen trans-fer correction factor α = 0.7. If more oxygen is charged than can be immediately dissolved, gas bubbles form in the crown of the pipe which, further down the flow, is completely or in part dissolved. Even with pressure reduction, e.g. in pumping pauses and in the course of the flow due to reduction of the manometric pressure head, the oxygen concentration re-duces but not in proportion to the pressure reduction, so that higher concentrations than saturation concentrations result ("oxygen supersaturation"). Sulphide problems are com-pletely overcome if, at the end of the pressure pipeline, 0.5 to 1 mg/l oxygen is still con-tained in the wastewater.

In most cases pure oxygen is delivered in liquid form in a tanker vehicle and is transferred to a storage tank from which it reaches the injection point via an air heated vaporiser with-out energy requirement. With a very large requirement self-production in an air separator plant can be economic. A metering and regulation system serves for dosing and control. Frequently, dosing takes place without a break for day and night charging via an automatic time switch. An electric coupling with one pump effects the dosing during pumping im-pulses only so that, with this, the flow rate of the wastewater and the highest possible ma-nometric pressure are utilised. A number of charging systems, such as lances, various types of nozzle or gassing hoses are liable to blockage and require considerable mainte-nance so that charging by means of a simple pipe adapter is recommended.

Oxygen escapes at pipeline high points through ventilation and air outlet valves in the form of gas. It is to be checked in operation whether, following closure of the valve, the increase of the pump energy requirement and the increased danger of pressure surges remain within acceptable limits.

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Often due to the temperature based reduced biological activity of the desulphuration agents, no pure oxygen needs to be charged in the times between December and April.

Pure oxygen is not bactericide or hazardous to health and, in part, oxidises already exist-ing reduced sulphur compounds, however, oxygen is also used for the oxidation of other wastewater component substances. Attention is to be paid to operating costs for the oxy-gen, the safety regulations for the handling of pure oxygen as well as operation and main-tenance by appropriately trained personnel. For economic reasons the procedure is hardly suitable for employment with drains with free wastewater levels.

5.2.4 Hydrogen Peroxide

Of all peroxides, hydrogen peroxide (H2O2), due to its effect and costs, is best suited for wastewater treatment. The clear, colourless, water mixable liquid is very stable in the pure state, however, breaks down already with small impurities due to catalytically functioning ions, whereby heavy metals are particularly effective. For transport and storage mainly containers made from pure aluminium or stainless steel are used.

Hydrogen peroxide has a heavy oxidising effect and irritates and/or burns skin, mucous membranes and eyes. The MAK [maximum working-place concentration] value is 1 ppm (represents 1.4 mg/m3). The substance is delivered in drums or in a tanker vehicle with concentrations of 35 or 50 % by weight. Due to the tighter safety precautions with the 50 % concentration, the 35 % concentration is preferably employed in wastewater plants. Input takes place simply using dosing pumps and a connection pipe, if required also as drop dosing into the pump sumps or chambers. The dosing quantity can be reduced with longer pressure pipelines if the dosing first takes place in the end range of the pressure pipeline (some 0.5 hours flow time to the pressure pipeline outlet).

With sulphide-free wastewater the hydrogen peroxide had a disinfecting effect and as oxy-gen source; the decomposition products are oxygen and water:

2 H2O2 → 2 H2O + O2

In wastewater containing sulphides, these are oxidised in precedence to other reduced compounds, whereby the reaction process is dependent on the pH value:

pH value < 8.5:H2O2 + H2S → S 2 H2O pH value > 8.5:4 H2O2 + H2S → H2SO4 + 4 H2O

With pH values up to 8.5, that is with normal communal wastewater, the stoichiometric re-quirement is 1 g hydrogen peroxide per 1 g hydrogen sulphide. In practice, due to side effects, some 1.5 to 2 times the quantity is to be applied. In the presence of iron and other metal ions always contained in communal wastewater, the reaction takes place within a few minutes.

The substance makes an overdosing possible, so that an oxygen reserve can be taken from the pressure pipeline into a subsequent gravity pipeline, causes no hydraulic prob-lems and is suitable for doing in the gravity pipelines. Attention is to be paid to the rela-tively high chemical costs and the safety conditions with handling.

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5.3 Operational Measures

5.3.1 Cleaning and Maintenance

Heavily polluted sewers often have anaerobic wastewater conditions and favour biogenic sulphuric acid corrosion. The most important operational measures for the maintenance of functioning wastewater discharge facilities is therefore cleaning and maintenance. In par-ticular the input of mineral substances into the sewerage system must be kept small, as the mineral components of deposits require very high flow rates in order that they can be flushed out of the sewer bottom. The mineral solids input can be most effectively reduced by frequent monitoring and cleaning of road gullies and dirt traps.

The regular cleaning of hydraulic stress points, such as initial sewer sections or sewers with storage capacity, also brings an improvement to the wastewater situation as the oxy-gen depleting deposits are removed regularly and the flow rate is increased.

In accordance with a German Federal Supreme Court (BGH) judgement, the complete sewer network has to be cleaned at least once a year (BGH Judgement of 11 July 1974 -Ref. No. III ZR 27/72). Continuous inspections should decide locally the necessity and fre-quency of cleaning of road gullies.

With sewers which are difficult to clean with a tendency to become dirty again a continu-ous cleaning process is sensible. With a process using travelling balls (beads) in the flow or gush-flushing, a permanent sedimentation of solids is prevented by their regular application (DINKELACKER, 1987).

If the cleaning possibilities are exhausted or impossible (e.g. in pressure pipelines), and sulphide forms, then the oxygen balance in the wastewater should be improved through suitable measures in order that no biogenic sulphuric acid occurs in the subsequent gravity sewer.

Wastewater systems should not only be systematically and comprehensively investigated but also more intensively and frequently investigated at stress and hazard points to avoid the formation of corrosion. The inspection results should be documented and regulated for all time intervals (date monitoring system).

5.3.2 Measures with the Occurrence of Corrosion

If corrosion damage occurs in existing systems, then subsequent protective measures are to be taken. Corroded sole areas of shafts or sulphur deposits on the shaft walls and pipe crowns, in combination with H2S, smell indicate that the discharge system is subject to an attack of corrosion. First, the cause of the corrosion attack should be determined (e.g. dis-charges containing acids, discharge of organic acids, discharges containing sulphide or biogenic sulphuric acid corrosion as a result of anaerobic wastewater conditions) in order to exclude the corrosion sources by preventing problematic discharges. With biogenic sul-phuric acid corrosion one should, under no circumstances, delay renovationmeasures too long that a prejudicing of the stability of structures has occurred.

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The cause of the occurrence of biogenic sulphuric acid corrosion often lies in the planning (comp. Chap. 5.1). A too small a gradient also causes a too small flow rate. Deposits form and there is anaerobic sulphur transfer. At the same time re-aeration only over the surface of the wastewater level is often insufficient. Also long flow paths to the wastewater treat-ment plant or, in particular, the operation of pressure pipelines with too large retention times have a negative effect on the wastewater quality. An improvement can often be achieved through additional or oxygen feed into the pressure pipeline.

5.3.3 Measures in Pump Sumps and Pressure Pipelines

Frequently problems occur at points, for example in pump sumps or in pressure pipelines with too long retention times. Here, the oxygen balance has first to be checked. An oxygen content of 1 mg/l in the wastewater normally suffices to prevent effectively the formation of sulphide. If the mean O2 content is lower, then first consideration is to be given as to whether an improvement through operational measures can be achieved. Individual opera-tional measures are:

− empty pump sumps as much as possible;

− reduction of pump sump volumes by lowering the switch-in point and thus increase the pumping frequency;

− flushing of the pump sump to avoid deposits by circulation of the delivered wastewater at intervals;

− emptying of pressure pipelines at the end of the pumping process (only practical with short pressure pipelines or small diameters).

If these measures cannot be completely or satisfactorily carried out the dosing of various chemicals or a pressure aeration/pure oxygen gassing are to be considered (comp. Chap. 5.2).

6 Bibliography [Translator's note: known translations are given in English only. Where there is no known translation into English a courtesy translation of the title is given in square brackets, after the original German titles].

ATV-A 110E Standards for the Hydraulic Dimensioning and the Performance Verification of Stormwater Overflow Installations in Sewers and Drains, 1988

ATV-A 115E Discharge of Non-Domestic Wastewater into a Public Wastewa-ter system, 1994

ATV-A 116E Special Sewer Systems Vacuum Drainage Service - Pressure Drainage Service, 1992

ATV-A 134 (draft) Planung und Bau von Abwasserpumpanlagen [Planning and Construction of Wastewater Pump Stations], 1998 [An English version dated 1982 exists]

ATV-M 143E Inspection, Repair, Rehabilitation and Replacement of Drains and sewers, 1998

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ATV-M 263E Recommendations for Corrosion Protection of Steel Compo-nents in Wastewater Treatment Systems Using Coating and Cladding, 1991

BICZOK, I Betonkorrosion - Betonschutz [Concrete Corrosion - Concrete Protection], Bauverlag Wiesbaden, 1968

BIELECKI, R. Biogene Schwefelsäure-Korrosion in teilgefüllten Abwasser- SCHREMMER, H. kanälen. [Bogenic Sulphuric Acid Corrosion in Partially Filled Sewers] Mitteilungen des Leichtweiß-Instituts für Wasserbau der Technischen Universität Braunschweig.

BOCK, E. Untersuchung zur Beständigkeit von Zementmörtel- SAND, W. auskleidungen duktiler Gußrohre gegenüber biogener KIRSTEN, K. Schwefelsäure-Korrosion. RAMMELSBERG, J. [Investigation into the Resistance of Cement Mortar Linings of Ductile Cast Pipes against Biogenic Sulphuric Acid]. fgr Gußrohrtechnik 25, p. 23-28, 1990

DINKELACKER, A. Kanalreinigung durch mitlaufende Kugeln hat sich im Zweijah-restest bewährt. [Sewer Cleaning Using Travelling Balls has Proved Itself in a Two-year Test] Korrespondenz Abwasser , No. 2, p. 161-165, 1987

GRÄFEN, H. et al. Die Praxis des Korrosionsschutzes [Corrosion Protection in Practice], Kontakt Studium, Vol. 64, Expert Verlag 7031 Grafe-nau, p. 37-63

HANTGE, E. Luftschadstoffe - Vermeidungsmaßnahmen und Auswirkun-MAINZ gen auf Boden und Wasser am Beispiel des Bundeslandes Rheinland-Pfalz [Air Pollutants - Measures of Avoidance and Effects on Soil and Water Using the Example of Rheinland- Pfalz]. New DELIWA-Zeitscrifft, Vol. 11, 1993

HVITVED-JACOBSEN, T. Hydrogen Sulphide Control in Municipal Sewers. In: Pre JÜTTE, B. treatment in Chemical Water and Wastewater Treatment, NIELSEN, P. H. Proceedings of the 3rd Gothenburg Symposium, Springer JENSEN, N. A. Verlag, Berlin, Heidelberg, 1988

IMHOFF, K. Taschenbuch der Stadtentwässerung [Handbook of Municipal IMHOFF, K. R. Drainage] 28th Edition, Verlag Oldenbourg, 1993

KEDING, M. Der Zustand der öffentlichen Kanalisation in der Bundesrep VAN RIESEN, S. ublik Deutschland - Ergebnisse der ATV-Umfrage 1990 [The ESCH, B. Status of the Public Sewerage System in the Federal Repub- lic of Germany - Results of the ATV Poll 1990], Korrespond enz Abwasser, 37th Year, Vol. 10, 1990

KLOPFER, H. Wassertransport durch Diffusion in Feststoffen [Water Delivery through Diffusion in Solids] Bauverlag GmbH, Wiesbaden and Berlin, 1974

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LAWA Leitlinien zur Durchführungen von Kostenvergleichsrechnungen [Guidelines for the Carrying Out of Cost Comparison Calculati-ons] Länderarbeitsgemeinschaft Wasser [Federal State Wor-king Group - Water] (LAWA), 1993

LOHSE, M. Schwefelverbindungen in Abwasserableitungsanlagen unter besonderer Berücksichtigung der biogenen Schwefelsäurekor-rosion [Sulphur Compounds in Wastewater Discharge Systems Paying Particular Attention to Biogenic Sulphuric Acid Corrosi-on], Publication of the Institute for Environmental Engineering, University of Hannover, Vol. 62, 1986

LOHSE, M. Der anoxische Druckleitungsbetrieb [Anoxic Pressure Pipeline Operation]. Korrespondenz Abwasser, No. 6, p. 631-637, 1987

MATTHES, W. Schadenshäufigkeitsverteilung bei TV-untersuchten Abwasser-kanälen [Distribution of the Frequency of Damage with Sewers Investigated Using TV] Korrespondenz Abwasser No. 39, Vol. 3, p. 363-367, 1992

POMEROY, R. D. The Problem of Hydrogen Sulphide in Sewers. Clay Pipe De-velopment Association, 1976

SAND, W. Die Bedeutung der reduzierten Schwefelsäureverbindungen Schwefelwasserstoff, Thiosulfat und Methylmercaptan für die biogene Schwefelsäure-Korrosion durch Thiobacillen [The Sig-nificance of the Sulphuric Acid Compounds Hydrogen Sulphide, Thiosulphate and Methymercaptane for Bogenic Sulphuric Acid Corrosion through Thiobacilli]. Wasser und Boden 5, p. 237-241, 1987

SGK Richtlinien zum Korrosionsschutz in Abwasseranlagen C6d, Korrosionskommission der Schweizerischen Gesellschaft für Korrosionsschutz (SGK) [Directive for Corrosion Protection in Wastewater Systems C6d, Corrosion Commission of the Swiss Association for Corrosion Protection], Technopark, Pfingstweid Straße 30, CH-8005, Zürich, 1994

STEIN, D. Schadenanalyse an Abwasserkanälen aus Beton- und KAUFMANN, O. Steinzeugrohren der Bundesrepublik Deutschlandwest [Damage Analysis on Sewers Made from Concrete and Vitrified Clay Pipes In the Federal Republic of Germany- West]. Korrespondenz Abwasser No. 40, Vol. 2, p. 168- 179, 1993

STRASSBURGER, Schweißen nichtrostender Stähle [Welding of Stainless F. W. Steels] Deutscher Verlag für Schweißtechnik, Düsseldorf, 1976

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THISTLETHWAYTE, The Control of Sulphides in Sewerage Systems. Butterworths, D. K. B. Sydney, Melbourne, Brisbane, 1972

TÖDT, F. Korrosion und Korrosionsschutz [Corrosion and Corrosion Pro-tection]. Walter de Gruyter, Berlin, 1961

US EPA Design Manual. Odor and Corrosion Control in Sanitary Sewer-age Systems and Treatment Plants. US Environmental Protec-tion Agency, 1985

WALTHER, W. Boden- und Gewässerbelastung in Niedersachsen durch Stof-feinträge aus der Atmosphäre [Loading of Soil and Bodies of Water in Niedersachsen Due to the Input of Substances from the Atmosphere]. Wasser & Boden, Vol. 1, 1994

7 Applicable Standard Specifications

[Translator's note: known translations are given in English only. Where there is no known translation into English a courtesy translation of the title is given in square brackets, after the original German titles].

BS 915 Specifications for High Alumina Cement (British Standard Insti-tution), Part 2, 1972

DAfStb Directive Richtlinie für Schutz-und Instandsetzung von Betonbauteilen [Directive for Protection and Repair of Concrete Components] 1990

DIN EN 196 Methods of Testing Cement, Parts 1 - 9

DIN EN E-197 Cement; Composition, Parts 1-2, 04/98

DIN EN 295 Vitrified Clay Pipes and Fittings and Pipe Joints for Drains and Sewers, 11/91

Requirements, Part 1, 11/96 Methods of Testing, Part 3, 11/91

DIN EN 476 General Requirements on Components for Gravity Drainage Systems, 08/97

DIN EN 496 Plastics Piping Systems; Dimensions, 08/91

DIN EN 512 Fibre Cement Pressure Pipes and Joints, 11/94

DIN EN 578 Plastics Piping Systems; Plastic Pipes and Fittings; Determina-tion of the Opacity, 09/93

DIN EN 579 Plastics Piping Systems; Crosslinked Polyethylene (PE-X) Pipes; Determination of Degree of Crosslinking by Solvent Ex-traction, 09/93

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DIN EN 580 Plastics Piping Systems; Polyvinyl Chloride (PVC-U); Test Method for the Resistance to Dichloromethane at a Specified temperature (DCMT)

DIN EN 588 Fibre Cement Pipes for Drains and Sewers - Part 1: Pipes Joints and Fittings for Gravity Systems, 11/96

DIN EN 598 Ductile Iron Pipes, Fittings, Accessories and their Joints in Sewerage Applications - Requirements and Test Methods, 11/94

DIN EN 637 Plastics Piping Systems; Components Made from Glass Fibre Reinforced Plastics, 08/94

DIN EN 681-1 Materials Requirements for Elastomeric Pipe Joint Seals Used in Water and Drainage Applications - Vulcanised Rubber, 06/96

DIN EN 698 Plastic Piping and Protective Piping Systems - Thermoplatsics, 10/95

DIN EN 705 Glass Reinforced Thermosetting Plastics (GRP) Pipes and Fit-tings - Methods for Regression Analyses and their Use, 08/94

DIN EN 727 Thermoplastic Pipes and Fittings - Determination of Vicat Sof-tening temperature (VST), 01/95

DIN EN 728 Plastic Piping and Ducting Systems- Polyofelin Pipes and Fit-tings - Determination of Oxidation Induction Time, 03/97

DIN EN 752 Drain and Sewer Systems outside Buildings Generalities and Definitions, Part 1, 01/96 Requirements, Part 2, 09/96 Planning, Part 3, 09/96

DIN EN 761 Glass Reinforced Thermosetting Plastics (GRP) Pipes - Deter-mination of the Creep Factor under Dry Conditions, 08/94

DIN EN 762 Plastics Piping Systems, 11/92

DIN EN 763 Injection Moulded Thermo Plastics Pipe Fittings - Test Method for Visually Assessing Effects of Heat, 09/94

DIN EN 773 General Requirements on Components for Hydraulically Driven Wastewater Pressure Pipes, 10/92

DIN EN 845 Festlegung für Hilfsbauteile Für Mauerwerk [Definition of Acce-sories for Brickwork], Parts 1 - 3, 12/92

DIN 846 Prüfverfahren für Hilfsbauteile für Mauerwerk [Test methods for Accessories for Brickwork], Parts 1 - 10, 12/92

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DIN 1045 Structural Use of Concrete; Design and Construction, 07/88

DIN 1053, Pt 1 Mauerwerk - Berechnung + Ausführung [Masonry - Calculations + Implementation], 11/96

DIN 1053, Pt 2 Mauerwerk - nach Eignungsprüfung [Masonry - Following Qualification], 11/96

DIN 1053, Pt 3 Reinforced Masonry; Design and Construction, 02/90

DIN 1053, Pt 4 Masonry; Buildings of Prefabricated Brickwork Components, 09/78

DIN 1164, Pt 1 Cement - Composition and Requirements, 10/94

DIN 2614 Cement Mortar Linings for Ductile Iron and Steel Pipes and Fit-tings; Application, Requirements and Testing, 02/90

DIN 4030, Pt 1 Assessment of Soil, Water and Gases for their Aggressiveness to Concrete; Principles and Limiting Values, 06/91

DIN 4030, Pt 2 Assessment of Soil, Water and Gases for their Aggressiveness to Concrete; Collection and Examination of Water and Soil samples, 06/91

DIN 4032 Concrete Pipes and Fittings; Dimensions, Technical Conditions of Delivery, 01/81

DIN 4034, Pt 1 Precast Reinforced and Unreinforced Concrete Components for Manholes over Buried Drains and Sewers; Dimensions and Technical Delivery Conditions, 09/93

DIN 4035 Stahlbetonrohre, Stahlbetondruckrohre und zugehörige Form-stücke [Reinforced Concrete Pipes, Reinforced Concrete Pres-sure Pipes and Associated Fittings], 08/95

DIN 4051 Sewer Clinkers; Requirements, Testing, Control, 08/76 Examples, 07/65

DIN 4060 Elastomer Seals for Pipe Joints in Drains and Sewers; Re-quirements and Testing, 12/88

DIN 4062 Cold Processable Plastic Jointing Materials for Sewerdrains; Jointing Materials for Prefabricated Parts of Concrete; Re-quirements, Testing and Processing, 09/78

DIN 4281 Concrete for Drainage Units; Manufacture, Requirements and Testing, 03/85

DIN 8061 Unplasticised Polyvinyl Chloride Pipes - General Quality Re-quirements and Testing, 08/94

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DIN 8062 Unplasticised Polyvinyl Chloride (PVC-U, PVC-Hl) Pipes - Di-mensions, 11/88

DIN 8063, Pts 1 - 12 Pipe Joints and Pipe Fittings for Unplasticised Polyvinyl Chlo-ride (Rigid PVC)

DIN 8074 High Density Polyethylene (HDPE) Pipes; Dimensions, 09/87

DIN 8075 (Draft) High Density Polyethylene (HDPE) Pipes; General Quality Requirements, Testing, 08/97

DIN 8077 Rohre aus Polypropylen, Maße [Polypropylene Pipes, Dimensi-ons],12/97

DIN 8078 Rohre aus Polypropylen Typ I + II, Allgemeine Anforderungen [Polypropylene Pipes Type I + II, General Requirements], 04/96

DIN 16 961, Pt 1 Thermoplastics Pipes and Fittings with Profiled Outer and Smooth Inner Surfaces, Dimensions, 02/89

DIN 16 961, Pt 2 Thermoplastics Pipes and Fittings with Profiled Outer and Smooth Inner Surfaces, Technical Delivery Conditions, 02/89

DIN 19 962, Pts 1 - 13 Pipe Joint Assemblies and Fittings for Polypropylene (PP) Pressure Pipes (Pts 1,3,6-8,11,12, 08/80; Pt 2, 02/83; Pt 4, 11/88; Pt 5, 05/94; Pt 9, 06/83; Pt 10, 10/89; Pt 13, 06/87)

DIN 16 965 Wound Glass Fibre Reinforced Polyester Resin (UP-GF) Pipes: Pt 1: Type A, 07/82 Pt 2: Type B, 07/82 Pt 4: Type D, 07/82 Pt 5: Type E, 07/82

DIN 16 968 Rohre aus Polybuten; Güteanforderungen [Polybutene Pipes; Quality Requirements], 12/96

DIN 16 969 Rohre aus Polybuten; Maße [Polybutene Pipes; Dimensions], 12/97

DIN 19 537, Pt 1 High Density Polyethylene (HDPE) Pipes and Fittings for Drains and Sewers; Dimensions, 10/83

DIN 19 537, Pt 2 High Density Polyethylene (HDPE) Pipes and Fittings for Drains and Sewers; Technical Delivery Conditions, 01/88

DIN 19 537, Pt 3 Prefabricated High Density Polyethylene (HDPE) Manholes for Use in Sewerage Systems; Dimensions and technical Delivery Conditions, 11/90

DIN 19 565, Pt 1 Centrifugally Cast and Filled Polyester Resin Glass Fibre Rein-forced Plastic (UP-GF) Pipes and Fitting for Buried Drains and Sewers; Dimensions and Technical Delivery Conditions, 03/89

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DIN 19 565, Pt 5 Prefabricated Glass Reinforced Plastic (UP-GF) Manholes for Use in Sewerage Systems; Dimensions and Technical Delivery Conditions, 11/90

DIN 19 850, Pt 1 Faserzementrohre und -Formstücke für Abwasserkanäle; Maße für Rohren, Abzweigen und Bogen [Fibre Cement Pipes and Fit-tings; Dimensions for Pipes, Branches and Bends], 11/96

DIN 19 850, Pt 2 Faserzementrohre und -Formstücke für Abwasserkanäle; Ver-bindungen, Maße [Fibre Cement Pipes and Fittings; Joints, Di-mensions], 11/96

DIN 30 672, Pt 1 Corrosion Protection Wrapping Tape and Heat Shrinkable Ma-terial for Pipes Designed for Service Temperatures up to 50° C, 09/91

DIN 30 675, Pt 1 External Corrosion Protection for Buried Pipes; Corrosion Pro-tection Systems for Steel Pipes, 09/92

DIN 30 675, Pt 2 External Corrosion Protection for Buried Pipes; Corrosion Pro-tection Systems for Ductile Iron Pipes, 04/93

DIN 38 405, Pt 26 German Standard Methods for the Examination of Water, Wastewater and Sludge; Anions (Group D); Determination of Dissolved Sulphide by Spectrometry (D 26), 04/89

DIN 50 919 Korrosion der Metalle, Korrosionsuntersuchungen bei Kontakt-korrosion in Elektrolytlösungen [Corrosion of Metals, Corrosion Investigations with Contact Corrosion in Electrolyte Solutions], 02/84

DIN 50 929, Pt 3 Corrosion of Metals; Probability of Corrosion of Metallic Materi-als when Subject to Corrosion from the Outside ; Buried and Underwater Pipelines and Structural Components, 09/85

DIN 50 930, Pt 4 Korrosion metallischer Werkstoffe bei innerer Korrosionsbelas-tung durch Wässer, Beurteilung der Korrosionswahrscheinlich-keit nichtrostender Stähle [Corrosion of Metallic Materials with Inner Corrosion Loading through Water, Assessment of the Probability of Corrosion of Stainless Steels], 02/93

DIN 53 521 Determination of the Behaviour of Rubber and Elastomers when Exposed to Fluids and Vapours, 11/87

DIN 61 855, Pt 1 Textile Glass; Glass Roving for Plastics Reinforcements; Woven Glass Filament Fabric and Woven Roving; Types, 04/87

DVS 2205, Pt 1 Berechnung von Behältern und Apparaten aus Thermoplast- [German Association en, Kennwerte [Calculation of Containers and Apparatus for Welding Technology] Made from Thermoplastics, Parameters, 06/87

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GKR*) R 7.1.12 Rohre und Formstücke aus PVC-U (weichmacherfreies Polyvi-nylchlorid) mit gerippter Außenoberfläche und glatter Innen-fläche mit Steckmuffen für Abwasserkanäle und -leitungen mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [Non-plasticised Polyvinyl Chloride (PVC-U) Pipes and Fittings with Ribbed Outer Surfaces and Smooth Inner Surfaces with Spigot and Socket for Sewers and Drains with the Quality Mark of the Quality Association for Plastic Pipes]

GKR*) R 7.1.13 Bauteile aus PVC-Hl Typ I (Polyvinylchlorid schlagzäh) mit pro-filierte Wandung und glatter Innenfläche - zur Auskleidung von Abwasserrohren - mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [PVC-Hl (Polyvinyl Chloride - Impact Resistant) Type I Components with profiled Walls and Smooth Inner Sur-faces - for the Lining of Wastewater Pipes - with Spigot and Socket for Sewers and Drains

GKR*) R 7.1.15 Coextrudierte, kerngeschäumte Rohre und Formstücke aus modifiziertem PVC-U mit Steckmuffe für Abwasserkanäle und - leitungen mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [PVC-U Co-extruded, Foam-filled Pipes and Fit-tings with Spigot and Socket for Sewers and Drains with the Quality Mark of the Quality Association for Plastic Pipes]

GKR*) R 7.1.16 Vortriebsrohre und aus Rohren hergestellte Formstücke aus PVC-U mit Steck Verbindungen ohne äußere erhabene Kon-turen für Abwasserkanäle und -leitungen mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [PVC-U Driven Pipes and Fittings Made from Pipes without Outer Raised Profiles for Sewers and Drains with the Quality Mark of the Quality Associa-tion for Plastic Pipes]

GKR*) R 7.1.19 Rohre mit profilierter Wandung und glatter Innenoberfläche aus weichmacherfreie, Polyvinylchlorid (PVC-U) mit Steckmuffe für Abwasserkanäle und -leitungen mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [PVC-U Pipes with Profiled Walls and Smoother Inner Surfaces for Sewers and Drains with the Quality Mark of the Quality Association for Plastic Pipes]

GKR*) R 7.1.23 Nichtbegebare Schachtunterteile und Regenrohrsandfänge aus PVC-U für Abwasserkanäle und -leitungen mit dem Gütezei-chen der Gütegemeinschaft Kunststoffrohre [Non-man Accessi-ble Lower Shaft Components and Stormwater Pipe Grit Cham-bers for Sewers and Drains Made from PVC-U with the Quality Mark of the Quality Association for Plastic Pipes]

_________________ *) GKR = Gütegemeinschaft Kunststoffrohre = Quality Association for Plastic Pipes

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GKR*) R 7.4.20 Nichtbesteigbare Schachtunterteile aus PP Typ 3 (Polypropylen Copolymerisat) für Abwasserkanäle und -leitungen mit dem Gü-tezeichen der Gütegemeinschaft Kunststoffrohre [Non-man-sized Shaft Lower Components Made from PP Type 3 (Po-lypropylene Mixed polymer) for Sewers and Drains with the Quality Mark of the Quality Association for Plastic Pipes]

GKR*) R 7.6.8 Nichtbesteigbare Schachtunterteile aus PE-M (Polyethylen mitt-lerer Dichte) für Abwasserkanäle und -leitungen mit dem Güte-zeichen der Gütegemeinschaft Kunststoffrohre [Non-man-sized Shaft Lower Components Made from PE-M (Medium Density Polyethylene) for Sewers and Drains with the Quality Mark of the Quality Association for Plastic Pipes]

GKR*) R 7.8.24 Kanalrohre und Formstücke aus UP-GF, gewickelt, mit dem Gütezeichen der Gütegemeinschaft Kunststoffrohre [Wound UP-GF Wastewater Pipes and Fittings with Quality Mark of the Quality Association for Plastic Pipes]

pr EN 1124 Pipes and Fittings of Longitudinally Welded Stainless Steel Pipes with Spigot and Socket for Wastewater Systems, 12/93

_________________ *) GKR = Gütegemeinschaft Kunststoffrohre = Quality Association for Plastic Pipes