Scope
This specification covers minimum requirements of materials, manpower, equipment, application, inspection, and testing of field joints corrosion coating for pipeline and in-field joint coating of onshore pipelines.
It shall be read in conjunction with the conditions of all specifications and documents included in the contract.
Field joint coating
Contractor shall, with care and diligence, execute the work in compliance with all laws, by-laws, ordinances, regulations, etc. and provide all services and labor, inclusive of supervision thereof, all materials, excluding the materials, indicated as Authorised GAS supplied materials in the Contract, equipment, appliances, or other things of whatsoever nature required in or about the execution of the work, whether of a temporary or permanent nature.
Reference code and standard
The following standards and codes of the latest edition have been used in this specification.
Governing Standard:
EN 12068 Cathodic protection- External Organic coatings for the corrosion protection of buried or immersed steel pipeline used in conjunction with cathodic protection- Tapes and shrinkable materials.
Reference Standard:
* SIS – 055900: This code is pictorial surface Preparation Standards for the Painting Steel Surfaces.
* SSPC – SP 1: This code is Solvents Cleaning, Steel Structures Painting Council.
* SSPC SP10 / NACE 2: This code about joint standard between the Steel Structures Painting Council and code NACE International for Near-White Blast Cleaning.
* ISO 8501-1: International Organization for Standardization Very thorough blast cleaning to SA 2 ½.
Quick link for more information:
Welding procedure specification (WPS) base thickness limit
Welder qualification test (WQT) thickness limit
introduction of ASME SECTION IX
Procedure qualification record (PQR)
* SSPC SP 1: This code about Steel Structure Painting Council for the Solvent Cleanings.
* SSPC-VIS 1-89: This code is Steel Structures and Painting Council for Visual Standard for Abrasive Blast Cleaned Steel.
In case of conflict between the requirements of this specification and that of the above-referred documents, the requirement of this specification shall govern.
Submittals by contractor
Prior to procurements of coating materials, the Contractor shall furnish four copies of, but not limited to, the following for qualification of the manufacturer and materials.
(a) Complete descriptive technical catalogs or data sheets describing the materials offered along with samples of anti-corrosion coating materials, its properties, and application instruction are applicable specifically to the project.
(b) Test certificates and results of previously conducted tests, for all properties of this specification.
(c) Reference list of previous supplies of similar material indicating the project details such as diameter, quantity, operating temperature year if supply, project name, contact person, and feedback on performance.
Once the Client/TPIA approval has been given, any change in material or manufacturer shall be notified to Client/TPIA, whose approval in writing of all changes shall be obtained before the materials are used.
The Contractor shall submit the coating procedure along with quality records and Inspection test plan compatible with this specification (Refer to Annexure-II) at least one week prior to commencement of the work for the approval of Client/TPIA.
Material and equipment requirement
General
* The Contractor shall be responsible to provide the coating material at the site in compliance with the requirement of this specification.
* Test Certificates shall be available to Client/TPIA for review before the commencement of work.
* The material and equipment for the joint coating material, material for blasting, primer, blasting hopper, air compressor, burners, Gas cylinders, etc, and shall be approved by Client/TPIA. Sandblasting shall not be allowed. Garnet will be the preferable blasting media.
* The contractor shall be responsible for arranging all manpower required for application, testing, and inspection of coating in the filed in accordance with this specification.
* Coating material shall be capable to withstand a maximum service temperature of 60°C. The material shall possess high dielectric strength, good tensile strength, and good resistance to thermal aging as mentioned in Table-1 & Table-2 of this specification.
Field joint corrosion coating material
* Heat shrinkable wraparound sleeve
a) Heat shrinkable sleeve shall consist of radiation cross-linked thermally stabilized, ultraviolet resistance, semi-rigid backing, with a uniform thickness of high shear strength and thermoplastic/copolymer hot melt adhesive.
b) The joint coating system shall utilize a solvent-free epoxy primer applied to the pipe surface prior to sleeve application. The backing shall be coated with thermo-chrome paint that will change color when the desired heating during the shrinking process is attained.
c) The wraparound sleeve shall be either in pre-cut form for a particular diameter or in bulk form to be field cut to a specific length depending upon the diameter of the pipe/fitting to be coated.
Cold applied tapes
* Cold applied tapes shall be made of polyethylene backing with a uniform thickness of the self-adhesive elastomeric compound. The primer used in the joint coating system shall be dried quickly on the pipe surface prior to the application of joint coating material, Cold applied tapes shall be used in areas as directed by Client/TPIA and they are not meant to replace the heat-shrinkable wraparound sleeve.
* The minimum thickness of the field joint coating shall be 2.5 mm on the complete finished field joint coating. Whereas, the thickness at the apex of the weld seam shall not be less than 2.0 mm.
* The field joint coating material shall be supplied with minimum following physical, chemical & electrical properties.
Procedure of applications
* The Contractor shall follow the joint coatings application procedure as per the manufacturer’s recommendation and guidelines or the minimum requirements specified in this specification whichever is more stringent. The contractor shall prepare a procedure indicating the mixing ratio and qualify the same procedure through vendor and Client.
* The Contractor shall submit and demonstrate to Client/TPIA, the proposed materials, and work procedures. The proposed procedures, materials, and equipment shall be approved by Client/TPIA.
Surface cleaning and preparation
* The contractor shall remove oil, grease, salts, and other contamination on the steel pipe surface by wiping with rags soaked with suitable solvents such as naphtha or benzene. Kerosene shall not be used for cleaning. The solvent cleaning procedure shall be in accordance with SSPC-SP-1.
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| Field joint blasting |
* Prior to surface cleaning, the surface shall be completely dried. The uncoated steel surface shall be then cleaned by shot blasting to SA 2½ of Swedish standard SIS-055900 and have a profile of 60-80 microns roughness. The roughness shall be checked by PRESS-O film or by other means as agreed by Client/TPIA. Shot blasting shall be stopped, in case, when Relative Humidity (RH) in the atmosphere observed is equal to or more than 85%.
* The ends of the existing pipe coating shall be inspected and chamfered prior to application and cleaned as per requirement. The unbounded portion of coating shall be removed and then suitably trimmed. Portions, where parent coating is removed, shall also be prepared as specified in this specification.
* The joint coating shall be applied immediately after the completion of surface preparations. Time-lapse shall not more than 30 minutes.
Application of Primer
Mixing of Epoxy Primer
* The approved epoxy primer shall be properly mixed as per manufacturer’s instructions. Epoxy primer mixing shall be carried out until a homogeneous mixture is obtained. The minimum DFT of applied epoxy shall be 200 microns.
* Immediately after completion of surface preparation, the approved primer shall be applied over the entire steel surface as per instructions given by the manufacturer. The epoxy primer shall be wet and tacky when the coating sleeve is applied. Necessary care shall be taken to protect the primed surface from the atmospheric dust particle. If the coating primer is damaged, the damaged area, the coating shall be clean and reprimed. The wet film thickness shall be measured to ensure the requirements as per the manufacturer’s recommendations.
Application of Heat Shrinkable Wraparound Sleeves
* The wraparound sleeves shall be of a size such that a minimum overlap of 100 mm is ensured prior to shrinking (after shrinking the minimum overlap will be 50mm) on both sides of the mill applied coating of the pipes.
* In the case where carrier pipe installed by direct boring/jacking, the overlap on the mill coating for the leading edges of the joints shall not be less than 200 mm. When the extra overlap is achieved by the provide an additional patch of the heat shrink tape/ wraparound, it shall be applied in such a manner that the square edge of the patch on the joint coating is in the direction opposite to the direction of boring /jacking.
* The bare steel surface shall be preheated over the surface to remove the mist before centering the wraparound sleeve. The minimum temperature for preheating shall be as recommended by the manufacturer. The temperature of the preheated surface shall be checked by using a pyrometer or thermometers shall be recorded.
* The wraparound sleeve shall then be entirely wrapped around the pipe positioning the closure patch\to one side of the pipe at 10 o’clock or 2 o’clock position and the edge of the undergoing layer facing upward. The overlap between the sleeve and closure patch shall not be less than 100 mm.
* A heat shrinking procedure shall be applied to shrink the sleeve in a manner such that all entrapped air is removed with the help of hand gloves and hand rollers. The complete shrinking of the entire sleeve shall be obtained without undue heating of mill coating and providing due bonding between pipe surfaces, sleeve, and pipe coating. The resulting coating shall be free from wrinkles, cold spots, and weld profiles visible on the sleeve.
Application of Cold Applied Tapes
* The cold-applied joint protection tapes shall be such that it can be applied by the spirally wrapping on the pipe.
* Approximately 100 mm of tape interleaving paper shall be pealed back and tape shall be applied with the compound side to the pipe. Whilst continuously removing the interleaving paper, the tape shall be spirally applied to provide a minimum of 55% overlap. Sufficient tension shall be applied to ensure good conformation, avoiding air pockets, and also continuously smooth out as the wrapping proceeds. The wrapping shall start and finish to give a minimum of 75-mm overlap on to the adjoining yard applied to coat.
* In the case where carrier pipe is installed by direct boring/jacking, the overlap on the mill coating for the leading edges of the joints shall be a minimum of 200 mm. In case of the direction of the spiral, wrapping shall be such that the square edge of the wrapping with a joint coating is in the direction of opposite to the direction of boring/jacking.
Inspection and testing
Visual inspection
A visual inspection shall be carried out for the following:
(a) Mastic extrusion on either end of the sleeve shall be examined (applicable for heat shrink wraparound).
(b) There should no sign of punctures, pinholes, or bend failure. The external appearance of the field joint coating sleeve shall be smooth, and free from dimples, air entrapments, or and voids formation.
(c) Weld bead profile should be visible throughout the sleeve.
(d) Position of the closer patch should be either 10 or 2 O’ Clock position.
(e) The entire closure patch shall have changed color uniformly (applicable for heat shrink wraparounds).
Holiday inspection
* The holiday detector used to check the damaged coating and pinhole in coating with the help of an accurate or calibrated DC voltmeter.
* The full circle holiday detector shall be approved by Client/TPIA. The test voltage shall be 5 kV + 5 kV/mm of the total thickness, subject to a maximum of 25 kV. The inspection of the sleeves shall be conducted only after the joint has cooled below 50 0C (applicable for heat shrink wraparounds).
* No field joint coatings shall be covered or lowered in the trench until it has been approved by the Client/TPIA.
Testing
* Client/TPIA reserves the right to remove and test, one of every 50 joint coatings or one joint coating of every day's production whichever is more stringent for peel test. The contractor shall provide all assistance in removing and testing field joint coatings. Peel tests shall be carried out after 24 hrs from the time of application.
* In the field joint coating sleeve peel test from each test sleeve, one or more strips of the size 25 mm x 200 mm shall be cut perpendicular to the axis of the pipe and slowly peeled off. Peel test shall be conducted between the wrapping and metal & the mill coating and betweens layer at the overlap with a joint coating (where it is applicable). The Peel Test shall be carried out in the presence of an authorized person or TPIA and the Contractor shall record the results.
* The required peel strength of the coating sleeve shall meet the requirement as specified, this specification, applicable to the 230 degrees Centigrade or 500 degrees Centigrade whichever is feasible. After removal of the strip, the bulk of adhesive shall remain adhered to the pipe showing no bare metal, otherwise, the test shall be considered as failed.
The adhesive layer on the pipe surface should be free of voids resulting from air or gas inclusion.
* If the sleeve took away for the test does not meet the requirements of clause 6.3.3, the adjacent two sleeves shall also be removed and inspected.
* If the adjacent two sleeves are acceptable the test rate shall be increased to one sleeve every twenty-five until Client/TPIA is satisfied. The test rate can then be reduced as per clause 6.3.1.
* If either or both of the adjacent two sleeves do not meet the requirements of clause 6.3.3, the field coating shall be stopped. (Refer to clause 7.0).
* GSPC GAS/TPIA reserves the right of 100% removal of sleeves if they are not convinced that the requirements of clause 6.3.3 are achieved.
* The coating thickness shall be checked or tested by non-destructive methods for each field joints. Ten measurements over the cut-back including one over the girth weld shall be taken and a minimum thickness of 2.00 mm shall be guaranteed on apex and an average thickness of 2.5 mm on pipe shall be measured only after the setting of the joint, preferably after 24 hrs.
Marking, protection, storage, and handling
* The contractor shall ensure the Manufactures have carried out all the quality control tests on each batch of material supplied. All such test certificates/ reports shall be submitted with each batch of the materials.
* Materials shall not be older than their period of validity at the time of application. Deteriorated and decomposed materials shall be disposed of and replaced by the Contractor at his own expense.
* The contractors shall ensure that the coating materials supplied by the supplier that is properly packed and punch or clearly marked with the following descriptions:
- Manufacturer’s name
- Materials Description
- Batch Number
- Date of Manufacturing and date of expiry
- Specific storage and handling instructions.
* All materials shall be stored and handled by the contractor in such a manner and types so as to prevent damage or deterioration.
* The contractor shall be provided and maintain mobile facilities equipped with all the necessary types of equipment and all it spares for the cleaning, coating, repairs, inspections', and tests.
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