Polypropylene coating for pipeline - influence of the extrusion process on the predicted coating lifetime

Onshore and offshore pipelines face a formidable range of hostile environmental agents, and the anticorrosion coating used for such pipelines must resist damage during transport, handling and laying, as well as withstand the continuous service typically designed for thirty years or more. When the pipelines are operating at high temperature the recognized best solution is a polypropylene grade with suitable stabilizer package. The coating is applied using extrusion processes and during these processes a material degradation can not be avoided, but the level of degradation can vary from extruder to extruder (i.e. from coater to coater), and according to the production rate. An extensive test program has been performed in order to evaluate how much the measured degradation can affect the coating lifetime. The paper presents detailed information on the test results as well as the obtained correlation.