284796797 German ATV DVWK a 168E Corrosion of Wastewater Systems Wastewater 1998 PDF

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GERMAN ATV STANDARDS

W A S T E W A T E R - W A S T E

ADVISORY LEAFLETATV-M 168E

Corrosion of Wastewater Systems -Wastewater

July 1998ISBN 3-34984-46-0

Marketing:Publishing Company of ATV - Wastewater, Waste, and Water ManagementTheodor-Heuss-Allee 17D-53773 HennefPostfach 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, HamburgDr. rer. nat. G. Heim, HildenDipl.-Ing. D. Kittel, PlaneggProf. Dr.-Ing. M. Lohse, MnsterDipl.-Ing. W. Meiger, KlnDipl.-Ing. U. Neck, DsseldorfDipl.-Ing. G. Niedre, Bonn (as guest)Prof. Dr.-Ing. H. Polster, BerlinDr.-Ing. J. Rammelsberg, GelsenkirchenDr.-Ing. F. Schmitt, EssenChem 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 inmachines, in particular data processingmachines, without the written approval of the publisher.

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

Original German Edition produced by:JFCARTHAUSGmbH & Co, Bonn


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Contents

Notes for users 5

1 Introduction and determination of terms 5

2 Corrosion processes 62.1 Soils and groundwater 62.1.1 Natural soils 62.1.2 Artificial soils 72.2 Wastewater 72.3 Sewer atmosphere 7

3 Construction and other materials 93.1 Cement bonded materials 93.1.1 Concrete and reinforced concrete 10

3.1.1.1 General 103.1.1.2 Chemical loading due to communal wastewater 103.1.1.3 Loading in the sewer atmosphere 143.1.1.4 Loading through soil and groundwater 143.1.1.5 Information on the avoidance of reinforcement corrosion 143.1.2 Mortar 153.1.3 Fibre cement 163.1.4 Composite pipes 163.2 Vitrified clay, sewer brick, glass 163.3 Metallic materials 173.3.1 Unalloyed and low alloy iron materials 17

3.3.1.1 Linings for pipes made from ductile cast iron and steel 173.3.1.2 Sheathing 183.3.2 High alloy, stainless steels 183.4 Plastics (PVC-U, PE-HD, PP, GFRP) 213.4.1 Preamble 213.4.2 Pipe materials 223.5 Sealing materials 243.5.1 General requirements on sealing materials for wastewater systems 243.5.2 Materials for and properties of sealing materials 24

4 Corrosion protection 25

4.1 Compound materials and linings 254.1.1 Pipe linings with new constructions 254.1.1.1 Factory produced pipe lining using PVC plasticised films 254.1.1.2 Factory produced pipe lining using unplasticised PVC web sheets 264.1.1.3 Factory produced pipe lining using web or knob HDPE sheets 264.1.1.4 Factory produced pipe lining using vitrified clay shells (ceramic plates) 264.1.1.5 Retrofitted pipe lining using plastic sheets 274.1.2 Shaft linings with new constructions 274.1.2.1 Factory produced shaft lining using plastic sheets 274.1.2.2 Shaft lining using GFRP sheets and elements 274.1.2.3 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 294.1.3.2 Renovation of man accessible profile sections 294.1.4 Shaft linings with renovation 294.2 Protective paints and coatings 304.2.1 Coatings on iron materials 304.2.2 Coatings on concrete surfaces 30

5 Notes for planning and operation 315.1 Notes on planning 315.1.1 Preamble 315.1.2 Location of wastewater treatment systems 315.1.3 Composition of wastewater 315.1.4 Indirect discharger operations 325.1.5 Drainage systems 32

5.1.6 Gravity pipelines 325.1.7 Pump stations and cross-sectionally filled pipelines 345.1.8 Soil and groundwater conditions 365.2 Addition of chemicals 375.2.1 Fundamentally suitable means 375.2.2 Addition of compressed air and pneumatic delivery 375.2.3 Addition of pure oxygen 395.2.4 Hydrogen peroxide 405.3 Operational measures 415.3.1 Cleaning and maintenance 415.3.2 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 collaborationwhich 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 correctand 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 correctapplication 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, wherebycorrosion 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, corrosionwas 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 theflow(KEDING et al., 1990). Until recently there has been extensive uncertainty on the partof 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 ofthe 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 noteasy in particular due to the numerous materials used in sewerage system constructionand the complex processes. It could also be associated with the fact that, previously inGermany, 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 andfunctional 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 toestimate parameters exist.

Recommendations for renovation are not part of this Advisory Leaflet, however, these canbe 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 directrelation to the chemical and physical properties of the soil with which the groundwater orthe 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 waterand 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 watercontent 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 soilswhich, 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, withcement 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) aredependent on it.

With natural soils only a few inorganic substances, in the first instance sulphates, chloridesand excess free carbon dioxide as well as organic substances, e.g. humic acid, come intoconsideration 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 foundin the vicinity of marshy soils, salt pans or with country roads spread with salt. The excesscarbon dioxide found in groundwater, which attacks unprotected metallic and cementbonded pipe materials has its origin primarily in the biological metabolisation of organicsubstances present in the upper soil layers. If the carbon dioxide manages to penetrateinto the subsoil with percolated precipitation water and, depending on the soil type, findsno reaction partner (e.g. calcium, magnesium), then it lowers, as dissolved aggressivecarbon 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 SO2emissions. This phenomenon is receivingincreasing 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, constructionrubble, industrial slag and rocky material resulting from mining operations, high contents ofmaterial corrosive substances can occur in the groundwater.

If a soil exchange with such materials is to take place with the backfilling of pipelinetrenches, 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 corrosionalone. It must also contain details on the water soluble substances from which a hazardingof the groundwater can stem. This is to be observed particularly with some of the recyclingmaterials 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 dischargeof wastewater one talks of communal wastewater (EN 1085/DIN 4045).

The basic loading of wastewater with inorganic substances results from the composition ofthe 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 wastewaterwhich can prejudice the stability of public wastewater systems. According to ATV StandardATV-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 stormwatercannot 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, asthe operator of public wastewater systems is also liable for subsequent damage, whichresult from unlawful discharge of wastewater, if the originator cannot be traced. Thereforecorrosion 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 humiditywith a tendency to the formation of condensation water. Through this, with unprotectedmetallic materials, corrosion can occur. The presence of hydrogen sulphide leads, in wetplaces above the water level to the formation of sulphuric acid with a correspondingly highdegree of corrosion with cement bonded and unprotected metallic construction materials.The biogenic sulphuric acid corrosion (BSAC) is induced mainly through the biologicalconversion 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 sewerwall;

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

The degradation processes in a sewer under aerobic conditions are shown in the left-handside of Fig. 1. The reduction of sulphates and albuminous compounds from the wastewatertake place in the sewer film and in deposits. If the dissolved oxygen is assimilated (withsewer 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 filmor 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 sewerfilm and the deposits, the reduced sulphur compounds are nevertheless again oxidisedbefore reaching the wastewater.

Under anoxic or anaerobic wastewater conditions a reduction of sulphate already takesplace in the upper layers of the sewer film and deposits. The from this resultant sulphidescan then diffuse, unhindered, into the wastewater. Depending on the pH value of thewastewater 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 thegreater is also the H2S potential that can be released into the atmosphere and which, inaddition 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 intoaccount 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 undissolvedform (bonded on metals). Thus, for example, the black colour of digested wastewater canbe traced back to finely distributed iron sulphide. The undissolved sulphides can, withnormal wastewater conditions, cannot contribute to the production of hydrogen sulphide. Ifthese are determined by the examination of the wastewater (which is often the case withconserved wastewater samples), a reduction for the undissolved sulphides from the de-termined total sulphide content must take place. With an extensively digested domesticwastewater one can set the content of undissolved sulphides at some 50 % of the totalsulphide 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 inwhich 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 thereis an enrichment of the biogenically formed sulphuric acid, mainly in the crowns of the pipewhich, 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 generalof 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 innumerous 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 significancewith 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 tothe soil and groundwater on the outside of the component or pipe (see Sect. 3.1.1.4) are tobe 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 orprestressed - or unreinforced. The Standard Specification DIN 1045 "Structural Use ofConcrete; Design and Construction" applies for the production and dimensioning of theconcrete. 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 forUnderground 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 thepossible 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 andthe frequency of cleaning processes with their mechanical influences on the surface of theconcrete, play a role. Therefore, the limiting values in Tables 1 and 2 are not identical withthe limiting values Table 4 of DIN 4030. The size of the limiting values given in Tables 1and 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 Sect2.2) 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 forwhich standard values exist in ATV Standard ATV-A 115 "Discharge of Non-domesticWastewater 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 normalcommunal 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 theloading (concentrate, duration) are to be assessed separately.

With the loading through normal communal wastewater a sufficient chemical resistance ofthe 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 canoccur 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 additionalrequirements:

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 thequantity 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 "FBSQuality Guideline - Concrete Pipes, Reinforced Concrete Pipes, Service Pipes and ShaftComponents for Underground Drains and Sewers (Published by the "FachvereinigungBetonrohre 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 sochanged through, for example, misuse, mishandling, unforseeable failure (accident) orlong-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, canbe 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 fulfilmentof the requirements, laid down in Table 2, on the concrete composition during the longestservice life in accordance with the LAWA Guidelines (LAWA, 1993).

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


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Type of attack Attacks through, forexample

Loading parametersof normal communalwastewater

Sufficient concrete resistance exists:

with a long-term load with fulfilment of fol-lowing requirements

on the concrete

Limiting values inwastewater

1 2 3 4 5

Loosening throughleaching

Soft water Not given Not applicable

Loosening throughacid attack

Inorganic and organicacids

pH value: 6.5 to 10 pH value 6.5 w/c 0.502) andwater 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 reactionAmmonia-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 HScement

1) In normal communal wastewater this value is not achieved. At most, in individual cases, a value in the given order is possible withthe 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 specialcomposition.


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Table 2: Limiting values for a temporary or short-term loading of concrete in thesewer 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. sulphuricacid, hydrochloric acid, nitricacid

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 Nolimitation

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 longerperiods of time, e.g. between two inspection dates during the course of ten operationalyears, 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 ashort time, the limiting values listed under "short-term (Column 3) apply. Such shortevents are seen as non-critical if they occur, at the most, once a week for a maximumof 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 corrosionthe sulphuric acid attacks the concrete chemically above the wastewater level causes aloosening attack on the surface of the concrete. The sulphates which result as reactionproducts simultaneously with the loosening attack on the concrete can, in principle, effectan expanding chemical attack in areas close to the surface (see also Sect. 3.1.1.4). Onecan, 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. Withexpected biogenic sulphuric acid attack a concrete with special composition in accordancewith 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 andgroundwater 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 toConcrete; 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 naturalsoils, 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 pressuredevelops in a fixed layer, which leads to swelling effects. Here, the formation of ettringiteand gypsum should be mentioned.

Lime dissolving carbon dioxide

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

Ca(OH)2+ CO2CaCO3+ 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)2is dissolved by water and is carried away.

Aqueous solutions of CO2react 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 insolution. This means that, in hard water, there must first be a high content of free carbondioxide 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 thecrack 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 componentsused in wastewater systems are very impervious. Therefore, for example, the possiblechloride content of normal communal wastewater does not promote corrosion. The generalpreconditions 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 thereinforcement can take place here.

3.1.2 Mortar

In general mortar is employed in wastewater systems as brick and joint mortar, as mortarfor the repair of components or for purposes of lining pipes (see also Sect. 3.3.1.1). Thecomposition 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 aswell 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 appliedaccording to the DAfStb [Service Instructions for Registrars and Supervisory Authorities]Standard for the Protection and Repair of Concrete Components (8/90). Depending on thetype of mechanical loading to be expected in the sewer, mortar of Loading Classes M3 orM4 as listed in the Standard can be considered., The Standard contains requirements onthe set mortar and details on the required verification.

The specialist technical rules are to be observed with the processing of mortar, so that anas 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 inthe 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 theremoval of all loose components and by wetting. With the use of mortar systems attentionis to be paid to the manufacturer's processing instructions which, as a rule, include thenecessary 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 asreinforcement and, for example, of pulp fibres as retention aid. In the hardened conditionthe fibres firmly embedded in the cement matrix increase the tensile strength of the fibrecement. Due to the dewatering of the cement lime, connected with production, a very im-

pervious cement composition results with very favourable water-cement ratios. Throughthis, 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, canbe employed. The most important standard specifications for prefabricated componentsmade from fibre cement for employment in wastewater networks are:

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

DIN 19 850 Faserzementrohre und -Formstcke fr Abwasserkanle[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 concreteenvelopment of, for example, vitrified clay pipes or plastic pipes. Such composite pipesare, as a rule, produced in concrete factories. They are used with particularly high staticand dynamic loading as well as in cases in which the particular protection of a concretepipe 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 withregard 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 manufacturedfrom 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 abrasionresistance) 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 hydrofluoricacid 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 withEN 296.

Sewer bricks, in accordance with DIN 4051 are used for structures and, in part, for largedimensioned sewers. Using clays they are formed mechanically and fired to vitrification. Assewer bricks are resistant against chemical attack the quality of the mortar used and itstechnically 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 forconcrete 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 wastewaterpressure pipelines are essentially unalloyed and low alloy steels and ductile cast iron.

These materials and the thereform produced sewers can, unprotected, suffer corrosiveattacks 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. Componentsmade from steel and ductile cast iron are therefore to be employed only with satisfactorycorrosion protection.

Table 3: Limiting parameters of the areas of application of cement mortar linings ofductile cast iron pipes, steel pipes and fittings taking onto account DIN2614 (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

SO42- mg/l 3000 solubility limit

NH4+ mg/l 200 2000

Ca2+ mg/l 1 0(stormwater)

Lime dissolving carbon dioxide mg/l 7 solubilitylimit(stormwater)

Parameters in the sewer atmosphere

H2S concentration in the free cross-section of the sewer as measure forthe 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 upwardsfrom 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 pollutiongas 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, theywere 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 constructionand 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/cratio 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 blastfurnace and Portland cements in accordance with DIN 1164 (S in accordance with DIN2614) 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 adhesivecapability can, in the long-term, be lost (e.g. polyurethane, polyurethane tar, polyethyleneetc.).

3.3.1.2 Sheathing

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

For on-site post sheathing of the pipe connections with soil of Soil Class III, sheathingsmade 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 corrosionprotective 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 resistantwith many corrosion loads. The resistance is governed by a very thin passive layer. Theeven surface abrasion with values < 10 m per year in the passive area is negligibly small.The passivity is essentially determined by the content of chromium which gives this steelits 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-nickelsteels with and without molybdenum addition come into consideration. In a draft for anEuropean 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 arethus 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 thewastewater which are significant; chloride can also accumulate in fixed deposits on steelsurfaces even with wastewater with non-hazardous chloride contents. In these cases, withpotentials which are greater than the pitting potential UL, there is a break through of thepassive layer with pitting as a result. It is pointed out, that also with atmospheric corrosionloads, corrosion hazardous chloride accumulations can occur in fixed deposits.

Table 4: Characteristics of some important stainless steels

Material designation Masses %

ISO683/13-

1986

EuronormSS-71

MaterialNo.

C Cr Ni Mo - Effec-tive

sum inmasse

s %

Pittingpotential

ULinmV1)

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 Mo17 12 2

1.4435 0.03 16 to18.5

11 to 14 2.0 to 2.5 - 25 + 600

21 X3 Cr Ni MoTi

17 12 2

1.4571(V4A)2)

0.08 16 to18.5

10.5 to14

2.0 to 2.5 5 % CTi0.5

25 + 6003)

- X3 Cr Ni MoN

17 13 54)

1.4439 0.04 16.5 to18.5

12.5 to14.5

4.0 to 5.0 N 0.12to 0.2

32 1200

1) According to GRFEN i.a. all potentials referred to the standard Hildebrand electrode2)

Designation in practice3) Assumed value4) German designation5) Do not use V2A in the sewer atmosphere

Pitting does not depend only on the chloride content but also on other factors given belowin 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 (GRFEN et al.). Inthe Table the steel with the Material Number 1.4439 is used as example for a steel withhigh W value.


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Redox potential URedox: if URedoxis 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 U L, 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, withwhich no crevice corrosion occurs, can be given. Analogous details in literature musttherefore 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 U

L, which underlines the danger-

ousness of crevice corrosion.

The possibility of intercrystalline corrosion as a result of a heat treatment of stainlesssteels, for example with welding, must be considered. This is a selective type of corrosionwith which the depositing of chromium rich carbides occurs at the grain boundaries. Thecorrosion 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 (steelMaterial 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, forexample, 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 resistanceagainst pitting. According to the draft DIN 50 930, Part 4, (1990), thin oxide films of a strawyellow colour can remain on the surface without prejudicing the corrosion resistance. Allother oxide films must be removed either through shot peening using glass beads, throughcareful 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 completelyavoided. Contact corrosioncan occur with metal conductive connections (direct electronconductive contact) of stainless steels with electro-chemical base materials, e.g. unalloyedsteels (DIN 50 919, 1984). Particularly endangered are small area components made fromunalloyed 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 atoften unavoidable, small faults in the coatings.

In summary the most important aspects, which should be observed with the employmentof 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 inwhich 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 castiron pipes.

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

Against the wastewater compositions which are permitted and occur in communal andother public drains the pipe materials given in Sect. 3.4.2 are generally to be seen aschemically 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 materialproperties are to be taken into account with the selection of the plastic for the respectiveapplication case. With coatings and linings, it must be further checked whether the specificparameters for the plastic processing can be maintained on the construction site and/or inthe 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 hightemperatures. Once manufactured, thermosetting plastics cannot be worked further. Theycan, however, be processed using machine procedures (milling, cutting, drilling) and joinedwith adhesives. Elastomers can no longer be thermally worked following chemical crosslinkage. They can, however, be processed mechanically and glued.

For application in sewers, plastic pipes and fittings as well as plastic shaft components andlinings, 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 thebasis of unsaturated polyester resins UP-GF

With the employment of the above named polymer materials in sewers, the following DINStandard Specifications are to be observed with regard to the requirements and qualityassurances:

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

In addition, for pipes with profiled walls made from thermoplastic materials, DIN 16 961 isto 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 fittingsmade 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 carrythe RAL Quality Mark of the "Gtegemeinschaft Kunststoffrohre (GKR)" [German QualityOrganisation for Plastic Pipes]:

nonascendable lower shaft components R 7.1.23R 7.4.20R 7.6.8

profiled sewer pipes and fittings made fromPVC-U R 7.1.12

R 7.1.19

sewer pipes and fittings made from modifiedPVC-U R 7.1.15


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sewer pipe lining components made fromPVC HI R 7.1.13

driven pipes and fittings made from PVC-U R 7.1.16

sewer pipes and fittings made fromwound UP-GF R 7.8.24

For employment in the area of private properties the components must correspond withthe Technical Rules published in the "List of Construction Rules A" (Bauregelliste A) of theGerman 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, shaftassemblies, and pipe lining components in accordance with the above given standardspecifications and directives, a sufficient chemical resistance for the normal service life ofsewers 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 aggressiveindustrial wastewater or for product pipelines in chemical operations. With aggressive me-dia the directions and corresponding resistance tables of the supplementary notes to thebasic 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 (DIN8061, Suppl. 1, DIN 8075, Suppl. 1, DIN 8078, Suppl. 1).

With pressure pipelines both DIN Standard Specifications (DIN 8061/62, DIN 8074/75, DIN8077/78) 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 surfacebut also from inside as small molecules can diffuse internally. Primarily organic solventsand 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 alsobe attacked under anaerobic conditions (e.g. in anaerobic tanks).

Local, mechanical damage can also be caused to GFRP pipes through incorrect handlingduring delivery (sudden loading) and in operation (incorrectly operated high pressurecleaning). At the damage sites the medium can penetrate into the bearing layers throughmicro-cracks in the gel coat and, depending on the structure, also into the bearing layersalong the fibres due to capillary forces (when employing long fibres). Through this thebearing 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 somanufactured 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 influencesfrom

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 deviatingfrom these, the respectively relevant loadings are to be taken into account. In waterprotection 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 53521.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 andTest Principles for Seals made from Elastomers with Increased Resistance Capabilityagainst 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 thrustseals in man accessible sewers and pipelines produced by pipe driving;

cold worked plastic sealing compounds in accordance with DIN 4062 are used only inindividual 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 guidancevalues 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 effectson the sealing function of the sealants.


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

For the area of the public sewerage system negative effects on sealants due to chlorinatedhydrocarbons (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 withpipe linings made from plastic widths. They are produced mainly from PE, PVC (free ofplasticiser) 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 installedwhich were anchored in the concrete using ribs. With these, films produced in the USAand in Germany a release of the external water overpressure from the groundwater due toencasing with concrete, is only possible at the upper 300 or at 360 through drainageholes 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 filmsoverlapped or were flush to each other. In both cases the connection, after laying thepipes, 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 hardhelical films. The 2 or 3 mm thick PVC hard profile sections are anchored to the concreteusing ribs and, with a 360 encasement in concrete, accept the full external water pressurefrom the groundwater and the diffusion pressure.

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

Due to the cases of damage which occur on the internal permanently elastic seal, preciseinformation on the actual chemical attack, for example as a result of biogenic sulphuricacid, 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 inseveral 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 manyplaces 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 usingPE-HD films with a full-surface overlay anchorage made from webs or knobs. The materialthickness (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 ajoint band. To ensure an even welding seam quality, extrusion welding, if possible usingcontrol, is to be preferred.

As the good welding capability and the corrosion resistance of the material is decisive forthe 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/landfilllinings, 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 aquality assured production in accordance with DIN ISO 9000.

If water pressure on the reverse side of the linings is to be expected, the lining systemshould, to avoid long-term deformation, be eased by means of stress relieving drillings inthe 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 8mm thickness, after laying the pipes. These sheets were subsequently stretched axially inone 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 openingsin the foot rails. The sheets are self-supporting but are not dimensioned for additionalstatic loading. The ends of the sheets are welded together. This solution has proved itselfagainst biogenic sulphuric acid attack in routine wastewater operation.

Due to the unlined base, however, other solutions are to be preferred for aggressivewastewater. 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 benoted that, with extreme operational conditions (surge flushing, reflected waves in front ofclosed gate valves) damage has already occurred on linings, which made an additionalsubsequent 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 isalso 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 websheets, 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 numerousfittings, recesses, outlets or sharp angled inlets is not economical and is problematic forabsolutely 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 onsite and numerous joints between the individual pieces, which are difficult to close. In suchcases 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, prefabricatedGFRP sheets made from polyester resin and glass fibres, with a thickness of 2 mm, isfixed to the concrete using plastic pegs. Subsequently there is a full surface, two-layerGFRP 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 a5 % 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 nottake 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, groundwaterwhich has appeared in the natural spaces between GFRP and concrete is to be drained offand 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 leastType 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 GFRPelements 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. Inorder here to avoid sulphuric acid corrosion to the cement bonded mortar joints, the jointsare 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 andnon-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 ofpump-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 internationalterms of DIN EN 752 should be used [already applied in this translation].

Table 5: Comparison of previously used and new standardised terms with therepair 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 sewersmaintaining the basic material

Rehabilitation Renovation

Production of new sewers by giving up ordestroying 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 topass external loads to the inliner by appropriate dimensioning which, with unsatisfactoryload bearing sewer pipes, makes a possible renewal unnecessary. A static calculation forrelining 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 domesticconnections with a technically sound corrosion safe sealing to the new inliner.

If this problem cannot be solved with the employment of appropriate robot equipment fromoutside 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 inlinersolution.

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 herevery simple to solve from the sewer.

Further renovation possibilities exist with sewers that remain stable, for example with theinstallation of prefabricated plastic sheets, e.g. made from GFRP, which are stretched over300 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 thebasis 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 acoating. 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 thermosettingresins.

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

Due to the temperature gradients in the coatings connected with this, a gradient for thepartial pressure of the water vapour also occurs so that the water molecules are pressedthrough 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 coatinghas 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 faultypre-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 appliedin 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) andthe 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 newcoating. 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 forProtection and Repair of Concrete Components (8/90) are to be applied. The Directivegives 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, theadhesion of the coating on the surface, and with this the durability of the protection isjeopardised. In addition the adhesive ability can, from the very beginning, be prejudiced asa 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 regardto 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 torupture of the coating. Following rupture the pipe material is wide open to the corrosiveattack. With biogenic sulphuric acid corrosion, the corrosion can even develop much moreintensively under the ruptured blister. Therefore attention is to be paid that coatings withsubstances 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 pipefaces, 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 particularlysuitable 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 sulphideproblem, catchment area and location are to be so determined that the wastewaterreaches the wastewater treatment plant from the source over the shortest distance and inthe 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 andthe analytical results attached to the request for tenders for the pipes. As parameters thefollowing, 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 tothe discharge of possible corrosively acting wastewater. Experience shows that one has toreckon 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 andtheir 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 causedalready with p


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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-timeand areas of back-up of reductions in cross-section, siphons, etc. If the necessary flowrates 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 loadsand 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 diameterschannels with small cross-sections can be used before for initial operational periods. Withtrunk 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 droppipes (ventilation pipelines) in houses. In addition, ventilation pipelines at provisional endsto a sewer, at intervals of ca. 25 m between shafts with man-accessible sewer sections, atthe 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 coverbox, 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 containingsulphides one should avoid bed drops due to stripping effects, unless special precautionsare taken and odour problems are not to be expected.

Fundamentally turbulence with wastewater loaded with sulphides is to be avoided. Withbranches 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; forthis 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 socketsplanned for latter connection are to closed off water tight in order that no wastewater canoccur in them.

Shut-off devices:

Openings for flushing and shut-off devices for pipeline flushing are recommended, at leastwith 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 onwastewater 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. Thepump sump should be emptied at short intervals, as far as possible completely, so thatsewer film on the walls and floor are at least partially aerated. Optimum solution is a largewastewater 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-A134).

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 largedischarge variations, e.g. with combined systems, a pipeline with small diameter should belaid for sewage and a further pipeline with larger diameter should be laid for combinedwastewater. In order that the wastewater in the combined wastewater pressure pipeline,with occasional several wee

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