Long Term Internal Pressure Strength of Spoolable Reinforced Plastic Pipe and Comparison of Qualification Requirement Based on API Specification 15S and DNVGL ST F119

Abstract

Abstract Spoolable non-metallic pipe (NMP) is recently getting increased popularity as material for onshore and offshore pipeline. Even though the material is generally more expensive than conventional carbon steel, the total life cycle cost (TLCC) reduction is driven by reduction of pipeline installation cost (faster lay rate, less manpower/equipment) and operational cost (no chemical injection to combat corrosion, less operational pigging and inspection). The most common types of spoolable NMP currently used are reinforced thermoplastic pipe (RTP) and thermoplastic composite pipe (TCP). Non-metallic composite material strength capacity to withstand internal pressure is naturally decreasing over time. As new material, limited long-term performance data are currently available for these types of pipes. To obtain the long-term strength degradation properties of the material requires long duration and expensive qualification process, which burden the development of these types of pipes. PETRONAS has performed series of qualification test for both RTP and TCP in collaboration with several manufacturers. The qualification was initially based on API RP 15S (edition 2006) with few additional testing to suit offshore application due to the recommended practice initially only covers spoolable RTP and generally for onshore application. The latest edition as specification (API Spec 15S) covers more general types of spoolable plastic line pipes, including bonded (fully non-metallic reinforced plastic pipe) and unbonded type (with metallic reinforcement). Recently DNV also issued DNV RP F119 in 2015, a recommended practice for TCP, which subsequently upgraded to become specification, DNVGL ST F119 in 2018. Both reference specifications/standards above have different requirements on how to design and qualify the reinforced plastic pipe, however in general, both are based on long term test requirement. This paper provides requirement of long-term qualification of the pipe, based on API RP/Spec 15S and compare the result if it is qualified in accordance to DNVGL ST F119. Different result in term of long-term strength capacity is observed between these two standards. This paper also explains the pros and cons and provide feedback to both referenced specifications above, to further improve the specification requirements and reduce the burden of either manufacturer or end user in performing qualification for the pipe.