A case study of design pressure and design life determination for non-metallic pipe using API RP 15S

SULPHATE-REDUCING BACTERIA (SRB) have become a major threat for offshore pipelines. Non-metallic pipe (NMP) – which is able to eliminate the SRB issues – has recently been considered as an alternative to conventional carbon steel pipe. NMP has been used for onshore pipeline applications for more than 50 years. Nevertheless, the pipe material requires a qualification programme for offshore standalone applications. In terms of the pipe structure, NMP consists of an outer layer, a reinforcement layer, and an inner layer. The NMP reinforcement layer is normally made by aramid fibre or glass fibre. NMP design pressure and design life is determined based on regression-curve analysis in accordance to API RP 15S and ASTM D2992. It is stated in codes that a minimum of 18 failure points should be satisfied in order to produce a regression curve. However, there are cases whereby minimum of 18 failure points are not met, hence resulting in incomplete actual test data for producing the regression curve. Thus, the design pressure and design life of NMP would be in doubt. A case study has been conducted in order to determine design pressure and design life (of 10 years and 20 years) using incomplete test data. The case study is essential due to insufficient test data being available, where-by only one sample for 6,000 to 10,000 hrs, and no samples for >10,000 hrs, were available, respectively. A sensitivity analysis was also performed by introducing dummy test data in order to determine the design pressure reduction for this case study in accordance to API RP 15S and ASTM D2992.