c-59

NATIONAL OIL CORPORATION

GENERAL ENGINEERING SPECIFICATION

GES C.59

CLEANING AND PURGING OF OIL AND GAS PIPELINES

Rev Date Description Checked Approved

0 1999 Issued for Implementation DL

Compiled by Teknica (UK) Ltd

GENERAL ENGINEERING SPECIFICATION CLEANING AND PURGING OF OIL AND GAS PIPELINES

GES C.59 Page 2 of 14 Rev 0 1999

INDEX

SEC TITLE PAGE 1.0 SCOPE OF SPECIFICATION 4 1.1 Introduction 4 1.2 Other NOC Specifications 4 2.0 DEFINITIONS 4 2.1 Technical 4 2.2 Contractual 5 3.0 DESIGN 6 3.1 Codes and Standards 6 4.0 FLUSHING AND CLEANING 6 4.1 General 6 5.0 WATER FLUSHING 6 5.1 General 6 5.2 Line Flushing 7 5.3 Fill-and-Dump Flushing 7 6.0 MECHANICAL CLEANING 7 6.1 Mechanical Scrubbers 7 7.0 PREPARATION OF THE SYSTEM TO BE CLEANED 7 8.0 SYSTEM EQUIPMENT PROTECTION DURING FLUSHING AND CLEANING 8 9.0 PROTECTION OF EQUIPMENT IN THE SYSTEM PROXIMITY 9 10.0 CHECKING CLEANLINESS 9 10.1 Water Flushing 9 10.2 Air Blowing 10 11.0 SAFETY ASPECTS 10 12.0 INERT GAS PURGING 10 12.1 Introduction 10 12.2 Inert Gases 11 12.3 Inert Gas Flow and Volume Requirements and General Rules 11 12.4 Sweeping Velocity 11 12.5 Volume of Inert Gas Required 11



SEC TITLE PAGE 13.0 PURGING METHODS USING INERT GAS 11 13.1 Continuous Flow or Sweeping 11 13.2 Alternate Pressurisation/Depressurisation Method 12 13.3 General Safety Aspects 13 14.0 HOT GAS NITROGEN PURGE 13 15.0 PURGING AIR OR GAS FROM PIPELINES 13 16.0 OIL PURGING 14



1.0 SCOPE OF SPECIFICATION 1.1 Introduction 1.1.1 This specification covers the minimum requirements for the cleaning and purging of above ground and buried

oil and gas pipelines. 1.1.2 This specification is intended for the pipeline Vendor/Contractor whose scope includes the cleaning and

purging of oil or gas pipelines after pipeline construction. The specification is written to cover in general terms the requirements for carrying out this procedure and is equally applicable to the Owner installed pipelines. Specific characteristics have not been taken into account, e.g. lengths, sizes, pressures, fluids etc, these will be established at the time of Purchase Order/Contract placement.

1.1.3 This specification does not cover the pipeline construction, these details are covered in GES R.04, and does

not cover the decommissioning of pipelines for abandonment. 1.1.4 In the event of any conflict between this specification and the applicable codes and standards, the

Vendor/Contractor shall inform the Owner in writing and shall receive written clarification before proceeding. 1.1.5 The Vendor/Contractor shall comply fully with the provisions laid down in this specification, any exception

must be authorised in writing by the Owner. 1.2 Other NOC Specifications 1.2.1 Where indicated in this specification, the following NOC Specifications shall apply: GES C.03 Safety Procedures on Construction Sites GES R.01 Pipelines Material Specification GES R.02 Pipeline Systems GES R.03 Pipeline Welding and Repairs GES R.04 Oil and Gas Pipeline Construction 2.0 DEFINITIONS 2.1 Technical The technical terms used in this specification are defined as follows: Flushing Defined in respect to this specification as the working through a pipeline with a liquid, usually water, to

remove debris. Cleaning Cleaning is defined as the total effort involved in the removal of undesirable items, materials, scale, rust,

oxidation, product residues and build ups. This may be achieved by a combination of pigging and flushing.



Cleanliness Cleanliness is defined as the status remaining after cleaning has taken place to ensure that all internal surfaces

exposed to the transmitted fluid are adequately clean to prevent unnecessary contamination and to meet the requirements of the commissioning specification.

Purging Purging is to drive out the remaining product in a pipeline after depressurisation. This is frequently carried out

by the use of nitrogen or other inert gas. Application 1) For newly constructed pipelines to drive out the remaining air after commissioning usually by a foam

"pig" and a buffer of nitrogen, then introducing the transmission product. 2) For existing pipelines, to drive out the remaining product and ensure the safety of the pipeline, or

section, for maintainence or repair. In this case the pipeline, or section, is completely filled with the inert gas.

Slug A pre-determined volume of liquid or gas other than the flow medium of the pipeline, contained between

spheres or pipeline pigs to perform a purging function, or to act as a buffer between two fluids. 2.2 Contractual The commercial terms used in this specification are defined as follows: Owner The oil and gas company, an associate or subsidiary, who is the end user of the equipment and facilities. Vendor The company supplying the equipment and material. Contractor The main contractor for a defined piece of work Sub-Contractor A company awarded a contract by a Contractor to do part of the work awarded to the Contractor. Inspection Authority The organisation representing the Owner or Vendor/Contractor that verifies that the equipment and facilities

have been designed, constructed, inspected and tested in accordance with the requirements of this specification and the Purchase Order/Contract.



Inspector A qualified individual representing the Owner, Vendor/Contractor or the assigned Inspection Authority, who

verifies that the equipment and facilities have been designed, constructed, inspected and tested in accordance with the requirements of this specification and the Purchase Order/Contract.

3.0 DESIGN 3.1 Codes and Standards ASME - American Society of Mechanical Engineers ASME B31.4 Liquid Transporation Systems for Liquid Hydrocarbons and Other Liquids. ASME B31.8 Gas Transmission and Distribution Systems. 4.0 FLUSHING AND CLEANING 4.1 General 4.1.1 The purposes of flushing and cleaning pipelines are two fold: a) To remove loose foreign matter from the inside of pipelines. Following the completion of construction, foreign matter such as welding rods, sand, earth, pebbles,

nuts and bolts, welders hammers, may remain in the lines. Such debris must be removed prior to commissioning and start-up in order to avoid line blockages and damage to equipment or sensitive components, e.g. compressors, pumps, orifice plates, turbine meters, control valve seats,etc.

b) To remove encrusted deposits from pipeline walls. Such deposits are principally rust, millscale, welding slag, grease and possibly temporary preservative

coatings, removed by pigging operations possibly propelled with compressed air prior to flooding. Cleaning may also be carried out when changing from one product duty to another, in particular loading and unloading terminal pipelines. Cleaning of existing pipelines is usually a production task.

5.0 WATER FLUSHING 5.1 General 5.1.1 Flushing generally falls into the following categories where applicable: - line flushing; - fill-and-dump flushing; - circulation flushing (if practically feasible). 5.1.2 Attention has to be given to the potential corrosive action of water (chloride ions on stainless steel, sea water

on carbon steel). Special water quality may be necessary for small systems (treated demineralised water or inhibited water).

5.1.3 Air blowing and water flushing can be used simultaneously. Compressed air is injected into the flushing water

in order to increase the turbulence. Monitoring such a method is not easy and is seldom used and if so must be used with great care, usually used on small systems.



5.2 Line Flushing 5.2.1 Line flushing water may be sourced from an existing firewater system in close proximity to the pipeline or a

temporary storage facility in remote locations. 5.2.2 This type of flushing normally involves taking a section of pipeline, and flushing it from a start-point to an

open end. A high velocity flow, in the order of 3-4 m/s should be achieved in order to be effective. In some circumstances additional pumping capacity will be required.

5.2.3 This method of cleaning is effective in removing loose debris from the pipeline but not particularly effective in

removing rust and millscale. To remove rust and millscale, flushing should be used in conjunction with pigging.

5.3 Fill-and-Dump Flushing 5.3.1 Fill-and-dump flushing is often used for cleaning pipelines. The method being quite simple, the adequately

vented line is filled with flush water which is then dumped to grade, the flush water dislodges loose debris and rust and carries it out of the pipeline. Environmental impact of the dumped water shall be investigated and approved before use.

6.0 MECHANICAL CLEANING 6.1 Mechanical Scrubbers 6.1.1 Whenever possible mechanical scrubbers or cleaning pigs should be used. These may be self propelled, i.e.

motor driven or pushed through the pipeline using fluid or water to propel the scrubber. 6.1.2 Before carrying out this type of cleaning it is necessary to confirm the pipeline, or a section of it, has been

designed to carry a pig, sphere or scrubber and if any equipment must be removed on a temporary basis, e.g. flow meters, in order to allow the pig, sphere or scrubber to pass through the pipeline. Various types of scrubber or cleaning pigs, are available ranging from steel bristle type, often known as a badger, to soft spheres that will distort under pressure to form a seal between the unit and the pipe wall as they are propelled through the line.

7.0 PREPARATION OF THE SYSTEM TO BE CLEANED 7.1 The following basic rules shall be adhered to: - Protection of sensitive equipment included in the system, e.g. control valves, turbine-type flowmeters,

orifice restrictions, will be carefully studied and items removed if necessary to prevent damage. Ideally, the design of the installation shall ensure that the pigs can be routinely run between sections.

- Protection of the equipment in the proximity of the pipeline discharge area shall be carefully

evaluated, in order not to damage equipment, e.g. electric motors or instruments, with water or flushed debris.



- Care shall be taken for pipelines designed for very low pressure service in order not to create, during flushing, a higher pressure in the pipeline than would be allowed by the design.

- Before draining a pipeline full of water, instructions shall be written stating that a vent may need to

be opened beforehand in order not to create excessive vacuum in the pipeline. - Thermal relief valves shall be installed where the shut-in pressure could exceed the design pressure as

a result of thermal expansion of static fluid or gas during cleaning operations of existing pipelines. 8.0 SYSTEM EQUIPMENT PROTECTION DURING FLUSHING AND CLEANING 8.1 During flushing or air blowing of pipelines, particles, e.g. sand, pebbles, rust, are carried along at high

velocities and may either damage fragile equipment when an impact occurs, or block small diameter pipe branches such as sampling points and instrument connections. All items of fragile equipment shall be removed from the pipeline before flushing, blowing or cleaning is carried out. Small connections shall normally be blanked off after removing any instruments and special cleaning carried out before re-installing the instruments.

8.2 The following are considered as fragile equipment items: - control valves; - safety valves; - orifice plates; - turbine-type flow meters; - pilot tube flowmeter; - venturi flowmeters; - rotameters; - in-line flow totalizers; - nozzles of ejectors; - traps; - internals of strainers, these may be replaced with temporary ones to filter foreign materials during;

flushing and cleaning. 8.3 This list is not exhaustive and shall be modified according to local requirements. - Process impulse lines for instruments will be isolated by means of the block valve on the impulse

pipe itself and, whenever possible, disconnected. This operation will be carried out by an instrument specialist.

- Thermowells may remain installed during flushing operations but must be removed for any operation

involving pigging equipment. - Butterfly valves and full-bore valves will be fully opened. - Orifice plates, when removed, shall be wired to the line in question until flushing has been completed,

or stored in the instrumentation workshop and clearly marked. - When a pair of flanges have to be separated for flushing or line blowing, check that the operation

does not create any stress on pump flanges or compressor inlet or outlet flanges.



8.4 Heavy control valves: The removal and re-installation of control valves entails considerable work and special handling equipment. In some cases it may be possible to leave the control valve in place.

- Control valve with a complete by-pass (3 valves): The cleaning flow may be directed through the by-

pass and the dead ends cleaned separately. During blowing or cleaning through the by-pass, the manual valves upstream and downstream of the control valve shall be closed.

- Control valve without a by-pass: A solution is to remove only the seat and the plug and then flush

through the valve. Depending upon the shape of the valve and the circulation direction, foreign matter can accumulate in the valve body and shall be removed manually or by flushing in the opposite direction.

9.0 PROTECTION OF EQUIPMENT IN THE SYSTEM PROXIMITY 9.1 During flushing and blowing operations, large quantities of dirty water and dirty air are discharged. This water

or air can contain pebbles, particles or rust and scale and may cause damage to any equipment in the vicinity of the discharge, e.g. breaking the glass of a pressure gauge. The water itself can damage insulation, electric motors, etc. Some protection shall be provided to:

- cover electric motors, piping insulation, junction boxes, instruments etc. with tarpaulins; - direct the flow outlet towards a place where there is no fragile equipment; - change the direction of a flow by rotating a flanged elbow; - attach a flexible pipe at the outlet to direct the flow to a desired place (for water flushing only); - add a spool piece to extend the point of discharge; - put a sheet of metal (insulation cover sheet for example) perpendicular to the flow, to break the flow

impact; - use temporary launching and receiving traps and suitable discharge systems. 1010.0 CHECKING CLEANLINESS The criteria for pipeline inner cleanliness depends on the use (oil or gas) and the internal finish of the pipeline;

uncoated, coated, passivated, stainless steel, rusty, etc. Pipelines shall be cleaned by pigging and flushing. 10.1 Water Flushing Inner cleanliness can be indicated as follows: - Colour of the water at the discharge. At the start it is frequently brown and becomes clearer as the

flushing proceeds. - Visual comparison of two samples of water, one taken at the inlet, the other one taken at the outlet.

When they are identical, the pipes are cleaned. - Strainers, located near the outlet and if necessary at some other places in the system. After a period

of flushing, the strainers shall be removed and inspected. If they are clean the flush may be considered to be complete.


GES C.59 Page 10 of 14 Rev 0 1999

- The mesh of the strainers will depend on the required degree of cleanliness but should be a maximum 0.004 in (0.1 mm) in the final flushing stage

- When the pipeline system has been flushed satisfactorily the pipeline shall be dewatered by pigging,

re-install any fragile equipment taking care not to allow dirt to enter the clean pipeline and, if necessary, fill with inhibited water.

10.2 Air Blowing The pipeline system or section may be dried, after cleaning and flushing, by air, blown through the system. 11.0 SAFETY ASPECTS 11.1 Air blowing is a potentially hazardous operation and all operations shall be rigorously controlled. a) A safety procedure shall be drawn up depending upon the job site rules and will be followed at all

times. b) An area of at least 100 ft (30 m) around the air exit point shall be roped-off and suitable signs posted.

Safety watchers should be appointed to ensure that personnel, other than members of the work operation team, do not enter the area during air releases.

c) Commissioning personnel carrying out the operations, e.g. operating the quick opening valves etc.,

must be provided with suitable ear protection, gloves, overalls and an eye/face shield (or goggles). d) It is recommended that systems to be air blown be prepared during the day and that actual blowing be

carried out at the end of the day shift when other personnel have vacated the area. In certain cases air blowing may be carried out by a night shift but this should not cause disturbances. e) The responsible person for each system shall ensure that all piping restraints and other equipment

protection are in place before carrying out air blowing. f) If a temporary reservoir method is to be employed, ensure that the equipment involved can withstand

the working pressure. Where vessels are concerned, it is preferable to have adequate safety valves in service. Air blowing should only be carried out after the lines and equipment to be pressurised have been successfully hydrostatically tested.

12.0 INERT GAS PURGING 12.1 Introduction 12.1.1 Inert gas purging is most frequently required to remove air from oil/gas pipelines in order to avoid the risk of

forming an explosive mixture. Air contains 21% oxygen (O2) and when mixed with combustible gases or vapours results in an explosive mixture.

12.2 Inert Gases 12.2.1 Nitrogen (N2). This is usually supplied in liquid form for subsequent vaporisation and use. Nitrogen can also

be supplied by molecular sieves or cryogenic units. Impurities consisting of traces of other gases such as oxygen (O2) and carbon dioxide (CO2) may remain in the nitrogen in concentrations ranging from 1000 ppm to 1% depending on the manufacturing process.


GES C.59 Page 11 of 14 Rev 0 1999

12.2.2 Inert Gas (N2 / CO2 mixture) This is generally produced in combustion type units which may be portable or permanent installations. A typical inert gas analysis would be N2 + CO2 in proportions of 88% N2 and 12% CO2. This gas normally contains minute traces of carbon monoxide (CO) and hydrogen (H2). Any water vapour present shall be removed from the inert gas prior to its utilization for purging.

12.3 Inert Gas Flow and Volume Requirements and General Rules 12.3.1 When purging oil/gas pipelines with inert gas (henceforth inert gas will be the term employed to describe

either nitrogen, or inert gas manufactured on site, unless otherwise stated) a high flow rate is required and has to be turbulent. Laminar flow is to be avoided since it will result in poor purging and possible hazard.

12.4 Sweeping Velocity 12.4.1 The Reynolds number shall be higher than 4000 to create the turbulent flow required. As a general guideline a

velocity of 10 ft/s (3 m/s) is an acceptable mean value for continuous purging. 12.4.2 When considering inert gas purging, the system in question shall be studied from a practical viewpoint. Most

installations are unable to furnish very large flows of inert gas, due to unit design. There is little point in concerning oneself with complicated velocity calculations if the equipment to provide sufficient inert gas does not exist.

12.5 Volume of Inert Gas Required 12.5.1 A volume of inert gas of 3 to 5 times the system to be purged, will be necessary to fully purge the line. The

final volume will be dependent on the desired O2 specification limits for the purged line. Typical inert gas supply pressure will be 90 to 100 psig (600 - 700 kPag).

12.5.2 When testing for O2, use a correctly calibrated oxygen meter or Draeger tube. Operators shall be completely

familiar with the use of this equipment. Final O2 checks shall be conducted by trained laboratory personnel using proven and calibrated equipment.

13.0 PURGING METHODS USING INERT GAS 13.1 Continuous Flow or Sweeping 13.1.1 This method should generally be used for small diameter, low volume pipeline systems. The principle

involved is to inject sufficient quantities of inert gas to create a turbulent flow in the pipeline, displacing the air ahead of it. Proceed as follows:

1) Assuming the system to be at atmospheric pressure, close all unnecessary vents and drains and install

plugs and caps except on vents and drains which are to be used for O2 sampling. 2) Ensure the pipeline to be purged is isolated from associated systems, either by valves or blinds. If

blinds are to be installed complete a system blind list. 3) Select an inert gas injection point or points and a vent point at the far end of the pipeline. If the inert

gas arrives via utility hose, ensure the hose is in good condition and that the injection point valve is open before opening the inert gas header valve. Sufficient injection points should be used to achieve the maximum flow available.

4) Open injection point valves and begin the purge. Ideally the atmosphere in the pipeline should be

analysed when the inert gas volume used is approximately 3 times the system volume. Before testing, simultaneously close inert gas injection valves and vent valves, to maintain the system under positive inert gas pressure.


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5) Sample for O2 at several points, especially on complicated pipeline systems, e.g. fuel gas headers. Check for dead ends.

6) When O2 readings are satisfactory, stop the purge whilst maintaining system pressure at

approximately 1.5 - 3.0 psig (10 - 20 kPag), or as required. A suitably calibrated pressure gauge shall be installed where easily visible and used to control the system pressure which may require topping up from time to time.

7) IMPORTANT NOTES: This method shall not be used for critical pipelines requiring very low O2 values. It is normally

suitable when criteria are not severe, e.g. O2 > 3%. A secondary problem with this method is that it may prove to be wasteful of inert gas and where

logistical problems arise the following method may be preferable, even for relatively small system. 13.2 Alternate Pressurisation / Depressurisation Method 13.2.1 This is the preferred method of inert gas for reasons of economy and safety. 1) Assuming the system to be at atmospheric pressure, close all unnecessary vents and drains and install

plugs and caps, except on vents and drains which are to be used for O2 sampling and venting. 2) Ensure the system to be purged is isolated from associated system, either by valves or blinds. If

blinds are to be installed complete a system blind list. 3) After ensuring that the inert gas supply is available, check the integrity of pressurising hose, if used,

and system pressure gauges. Gauges shall be situated so as to be easily visible from the injection point valves.

4) Pressurise the system to between 15 - 30 psig (100 - 200 kPag). Never exceed system design

pressure even if safety valves are in service. 5) Let the line stand for approximately 30 minutes to allow the gases to become homogenous. After this

30 minute period, depressure the system as rapidly as possible via the largest diameter vent or vents on the system.

6) Repeat this operation but stop depressuring at about 1.5 - 3.0 psig (10 - 20 kPag) and take an O2

reading. The O2 at this point should, theoretically, be in the region of 4 to 5%. Samples shall be taken from several points, depending upon the magnitude of the system, and averaged.

7) According to the O2 content requirement, repeat the pressurisation / depressurisation operation until

the specification is met. 8) When O2 results meet the required specification, maintain the system under a positive inert gas

pressure until ready for use. Warning notices shall be posted. 9) NOTES It is better to pressurise / depressurise 5 times up to 15 - 30 psig (100 - 200 kPag) each time, than to

pressurise / depressurise once up to 75 psig (500 kPag). In the first case the theoretical final oxygen content is 25 = 32 times less than the original one. In the second case the theoretical final oxygen content is only 5+1 = 6 times less.

Purging can be speeded up by pulling a vacuum on the system before pressurising. However,

attention shall be paid to the pipeline design before this operation is considered. Under no circumstances shall a vacuum be applied indiscriminately to equipment without first

checking that the equipment is capable of withstanding vacuum conditions.


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13.3 General Safety Aspects 1) Inert gas is dangerous. Always remember that an atmosphere containing less than 21% oxygen will

not support life. 2) Always carry out a careful scrutiny of flexible hoses used in purging operations. 3) If an inert gas distribution system is used, it is normal practice to turn closed, any spectacle blinds

following use of the injection point. Failure to do so may result in petroleum products entering the inert gas distribution system.

14.0 HOT GAS NITROGEN PURGE 14.1 In order to enhance the moisture removal, the nitrogen purge may be heated. This acts as a scavenger for

moisture and is appropriate to use in lines where water removal is a major issue. 14.2 In order to perform such work, it is necessary to be equipped with heating equipment which operates at about

100oF (38oC). All safety precautions must be followed. Purging is repeated until the line is free from moisture. This can be checked by passing a Draeger tube carefully through the venting gas stream.

15.0 PURGING AIR OR GAS FROM PIPELINES 15.1 When a pipeline full of air is placed in service, the air may be safely purged with gas provided that a

continuous flow of gas is introduced at one end of the line and the air is vented out the other end. The gas flow should be continued at the lowest velocity practical to maintain venting of the air, without interruption, until the vented gas is free from air. The vent should then be closed. A sphere may be used to segregate the air from the product, alternatively, inert gas trapped between two spheres may be used to segregate at the air/gas interface.

15.2 In cases where gas in a pipeline system is to be cleared with air and the rate at which air can be supplied to the

line is too small to make a procedure, similar to but the reverse of that described above, feasible, a slug of inert gas shall be introduced to prevent the formation of an explosive mixture at the interface between gas and air. This is normally separated from the gas and air by the use of spheres. Nitrogen or Carbon Dioxide may be used for this purpose.


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15.3 If a pipeline system, or auxiliary equipment, is to be filled with air after having been in service and there is a

reasonable possibility that the inside surfaces of the facility are wetted with a volatile flammable liquid, or if such liquids might have accumulated in low places, purging procedures designed to meet this situation shall be used. Purging of the line until all flammable liquids have been removed is recommended. Filling of the line with an inert gas and keeping it full of such gas during the progress of any work that might ignite an explosive mixture in the facility is an alternative recommendation. The possibility of striking static sparks within the facility shall not be overlooked as a possible source of ignition.

15.4 Suitable precautions shall be taken whenever a pipeline system which is full of air is cleared with a

combustible gas. The gas and air shall be cleared to a safe location where no collection can build up. In no event should the pipeline be cleared into an area where there is a possible source of ignition. During the clearing operation smoking shall be strictly prohibited.

16.0 OIL PURGING 16.1 When all mechanical cleaning and any necessary hydrotesting or pneumatic testing has been completed the

pipeline system is to be vented and drained. 16.2 The line may be filled with a suitable oil and then drained or oil may be circulated around the pipeline system.

In either event the oil must be circulated through a filtration system before returning it back to a storage tank. 16.3 The oil may be light or heavy but must be determined as compatible with the products that will be run in

service. Waste oils may be used providing they pass through a filtration process before injection into the system and are filtered upon return to the tank.

16.4 Any evidence of contamination or debris in the filters will require the pipework to be reflushed. S:\NOC9077\ADMIN\SPECIFICATIONS\C-SERIES\C-59\GESC59RF

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