Prior to shot blasting the pipe is preheated to at least 3 degrees above the dew point. This removes any unwanted dew and moisture on the surface of the pipe. After pre-heating, the pipe is shot/grit blasted to ensure that the external surface is thoroughly cleaned as per SSPC SP10, and Sa 2 ½. The shot/grit blasting process also ensure proper surface profile of between 2-3 mils.
Immediately after the pipe surface is shot/grit blasted, it is visually inspected to ensure that the requirements of surface profile are met. The pipe is transferred to the coating line, where after receiving a chromate wash(if required), the pipe is heated to temperatures in the range of 180-220 degrees centigrade. This ensures that the epoxy, which is electro statically applied on the external surface of the pipe adheres to the steel surface. Thereafter the co-polymer adhesive and the polyolefin topcoat are extruded on the steel pipe. The pipe is then quenched with a water bath, and prior to cut-off is online holiday tested. As per the requirements of the specifications, the ends of the pipe are then cleaned to remove up to 150 mm of the coating.
The quality tests that are required as per the requisite specifications are then carried out and the results noted. The peel test, impact resistance test, indentation resistance test, Cathodic disbondment test, and Hot Water Soak Tests are carried out in-house in the quality lab. A summary of PE coating requirements and our performance is given in the file attached.
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