Annulus Testing as the Integrity Management Method for Steel-Reinforced Thermoplastic Pipe

Abstract

Decarbonization efforts by the energy industry have driven a strong focus on implementing corrosion-resistant non-metallic pipe technologies. Reinforced Thermoplastic Pipes (RTP) comprise a popular family of pipe products that combine high-pressure ratings with the benefits of spoolable products. Due to their multi-layered structure, RTP pipe products face challenges when operators try to employ traditional non-destructive evaluation (NDE) technologies for inspection and integrity verification. This creates a unique opportunity for RTP pipe manufacturers and pipeline operators to employ innovative inspection and maintenance practices. Construction damage is statistically the most common cause of failures in RTP pipeline systems. RTP pipes typically include an inner polymer liner, an intermediate reinforcement layer, and an outer polymer shield. The role of the shield is to protect the reinforcement material from external environmental elements such as soil and groundwater. Construction damage that involves only the external pipe shield and does not involve the pipe reinforcement is challenging to detect. If left undetected, such damage may lead to the deterioration of the reinforcement material over time, potentially resulting in a loss of containment. Some RTP pipe products, including Flexible Steel-reinforced Pipe (FSP), have a built-in annulus space between the liner and the shield. This inherent feature allows for the introduction of an annulus test for a pipeline constructed from the FSP. The annulus test is a pneumatic pressure test that confirms the integrity of the pipe shield at different stages of the pipeline life cycle. Annulus testing performed during pipeline operation or maintenance offers an excellent way to verify the nonmetallic pipeline integrity and detect external damage that may have occurred, for example, due to third-party intervention. Once external pipe damage is detected, the operator can take steps to repair the pipeline and prevent a potential loss of containment. While such testing is well-known in the offshore pipeline industry, it has not been widely used in composite onshore pipeline applications. Modern pipeline design, construction, and integrity management standards are beginning to acknowledge and incorporate RTP pipe products and associated best practices. In 2022, the newly published API Recommended Practice 15SA named annulus testing as a method for integrity verification of spoolable reinforced line pipe products. This method has become an essential part of Preventative Maintenance and Inspection Programs for composite pipelines. This publication explains how the annulus testing method makes composite pipelines safer and improves their long-term performance.