Following content provides a sample Pipeline Wrapping and Coating Specification and indicates important inspection and testing requirements.
1.1.1 External surface of pipe shall be cleaned before initial priming by blast cleaning (Sa 21/2) and the minimum surface finish for blast cleaning shall be as per SIS 055900.1 or any specified standard by client.
1.1.2 The cleaning process shall remove all oil grease, weld slag, rust and any other foreign matter from the pipe external surface.
1.1.3 The applied cleaning method shall not result thinning of the pipe wall beyond the limits of the pipe specification.
1.1.4 Cleaning shall be carried out immediately before application of the priming coat.
1.1.5 Piping shall not be carried out under damp or frosty condition unless approved means of heating and drying of pipes are used. Any pipe that has become wet after cleaning and priming, or stood overnight before wrapping shall be re-cleaned to the required standard and re-primed.
1.1.6 The primer shall be applied in a thin layer without runs, sags, drips, holidays (gaps or voids) or other defects. Should any defects be found in the primed surface, the pipe shall be re-cleaned and primed to the required standard and to the satisfaction of principal/engineer.
1.1.7 Freshly primed pipe shall be properly supported on racks, and allowed to be uncontaminated by moisture, dirt or other foreign matter.
1.2 COATING SYSTEM (WRAPPING)
1.2.1 The protective wrapping shall consist of a coating system employing primer, laminated inner tape wrap and outer wrap.
1.2.2 The laminated inner tape wrap shall be butyl rubbed on polyvinyl chloride backing.
1.2.3 The outer tape wrap shall be polyvinyl chloride white in color. For normal application, the outer wrap thickness shall be 0.81 mm. In rocky ground and where specified the outer wrap thickness shall be 1 mm.
Materials shall be supplied from the same Vendor and consist of the followings:
Primer shall be a fast-drying compound, compatible with the laminated tape suitably compound to produce a liquid coating material that can be readily applied cold by brushing or spraying to produce an effective bond between the bare pipe surface and the subsequent coat of laminated tape. It shall be free flowing at the application temperature ranges and have the ability to cover voids, pits and welds, and shall be resistive to fungi bacteria.
The physical properties of primer shall be as followings:
2.2 INNER WRAP
A laminated tape consists of two layers as followings:
The laminated plastic tape shall have a backing of stabilized polyethylene and a primer activated adhesive mass of butyl rubber. The whole tape shall be resistant to bacterial, fungi, vegetable and different salt solution presenting in the ground.
It shall be suitable for line travel application and shop coating with wrapping machine.
The physical properties of the inner wrap shall be as followings:
No cracks shall be seen during application at low temperature (-20 °C). The laminated tape and primer shall be supplied by the same manufacturer.
2.3 OUTER WRAP
The outer wrap shall be polyethylene plastic tape suitable for machine application over the inner wrap. It shall give protection against mechanical damage over inner wrap during pipe lowering-in and back-fill operations. It should also provide protection against solar and U.V. radiation.
The physical properties of the outer wrap shall be as followings:
These items must be monitored by NACE Inspection service provider company.
2.4 PLASTIC ROCKSHIELD
Plastic rock shield shall consist of a matrix of spaced ribs of high density polyethylene with good impact resistance. It shall be resistant to shock, fungi, natural and artificial agents contained in soil. The grid pattern shall be so designed as to encourage the passage of cathodic protection current to the coating surface. Methods of fasting shall be circumferential strapping with 15 mm wide plastic bands and associated buckles. Rock shield shall be used over outer wrap to protect it against mechanical damage, which will be applied at water crossings, rocky/semi-rocky crossings where, continuous concrete weighting/concrete set on weights shall be employed.
The physical properties of rock shield shall be as followings:
2.5 HAND WRAPPING TAPE
The laminated plastic tape shall have a backing of highly flexible polyethylene and a mass of primer activated coat of butyl rubber. It shall be highly conformable at Low temperature and suitable for hand wrapping of tees, bend and other irregular shape fittings of small diameter up to 4" to be buried in the ground and subject to cathodic protection currents. It shall be resistant to bacteria, fungi and agents present in the soil. The tape shall be designed for use with its own primer.
The physical properties of the tape shall be as followings:
Primer and wrapping system shall comprise the followings:
|Nominal Pipe Size||Minimum Overlap|
|UP to 12||12 mm|
|14 to 20||25 mm|
|Over 20||50 mm|
Where manual application of coating is used the inner and outer tape wrap shall not be wider than 150 mm.
Prior to welding the pipe wrapping shall commence and terminate a minimum distance of 150 mm from each weld joint. This bare area shall be prepared and wrapped in accordance with this specification after successful hydro-test.
5.1 Pipe coating shall be subjected to 100% visual inspection and 100% inspection with an electrical holiday detector before being lowered into the trench.
5.2 Visual inspection shall ensure that the coating is continuous, the overlap is correctly maintained and that there is no wrinkle in the tape. The holiday detector shall be used to check that there is a continuous coating over the pipe surface.
5.3 The voltage of detector shall be regulated to produce an ARC which just bridges an air gap equal to twice the distance between the outer face of coating and outer steel face of the pipe.
5.4 The holiday detector's setting shall be checked at least twice per day while it is in use.
5.5 At no time shall the holiday detector be permitted to remain stationary around a coated pipeline with the operating voltage switched on.
5.6 All defects, whether discovered visually or by means of the holiday detector, shall be clearly marked.
5.7 After test samples from inside of the roll have been aged for 30 days in an air circulating oven at a constant temperature of 60°C, the tensile strength and the elongation shall be determined at 22°C by ASTM D1000. An average value for tensile strength and elongation shall not be less than 80 percent of the original un-aged value.(Heat Aging)
These items must be checked by NACE Inspection service provider.
6.1 Repairs of holidays and damaged areas due to destructive tests shall be made in accordance with procedures specified in each individual coating system. For example, all holidays detected, such as damaged or flowed areas or mislaps, shall be repaired by peeling back and removing the outer and inner layers from the damaged area. The holiday area shall then be brushed with primer and then a length of inner-layer tape shall be wrapped around the pipe to cover the defective area or a patch of inner-layer tape shall be applied directly to the defective area as specified by the company. The minimum lap at the damaged area shall be 100 mm all around. The repaired area shall be tested with a holiday detector after the repair is completed. If no holidays are found, the repaired area shall then be covered with outer-layer tape with a minimum lap of 100 mm beyond the inner tape patch. These items must be monitored by NACE Inspection service provider company
6.2 All repairs shall be re-tested for holidays.
6.3 The welded joints shall be cleaned, primed and coated according to specified procedures.
6.4 After field repairing of coating and before lowering the pipe into the ditch, the pipe shall be tested for holidays again. All defective places shall be plainly marked and repaired using the methods of identified.
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