Turning a Well-Known Anti-Corrosion Coating System into an Electrical Insulation System for Heated Pipelines

Abstract As a major improvement to a Direct Electrical Heating Pipe-in-Pipe system reliability, an additional 3-layer polypropylene (3LPP) coating is used as electrical insulation system. 3LPP is a widely used system for subsea anti-corrosion application, that needs to be qualified for the electrical insulation purpose. Scope of the paper is to present the qualification path of the 3LPP electrical insulation system, from the requirement definition and product selection to the qualification plan execution and results application. Qualification of an anti-corrosion system for electrical insulation purpose requires gathering as much data as possible, mainly on its electrical characteristics. The steps followed to qualify the 3LPP for electrical insulation are the following: 1/Full characterization of the system under different temperatures. These data are used to properly size the system and adjust the electrical models; 2/Accelerated aging of the system for a 25-year life representativeness. Considering the few available data on the 3LPP aging, an extended electrical and thermal aging campaign has been performed. The aging test protocol has been designed to validate the system aging over 25 years, including a thermal cycling aging and a continuous multifactor thermal and electrical aging, and secondly to challenge/validate the aging data from literature. All the qualification steps have been completed on an extended number of scale-one samples to reach a maximum level of confidence. The results show a good viability of the product for the given purpose. The material properties are in line with the anticipated values, validating both the sizing model and finite element analysis model. The aging behavior of the system is found to be even better than expected (from literature), meaning that the system is withstanding 25 years of service life without reaching the viability threshold or end of life criteria. The work performed and presented in this paper brings additive information to the 3LPP range of use and brings a new occurrence of plastic materials multifactor aging test.