Engineering critical assessments of subsea pipelines under high-pressure/high temperature service conditions

Abstract

Due to the world’s continuously increasing energy demand and currently limited alternatives, the exploration and exploitation activities of offshore oil and gas are heading into deep waters. In this process, subsea production systems are faced with severe challenges from development environments such as high-pressure/high-temperature reservoirs. As the part of a subsea production system that occupies most extension in space, failures of subsea pipelines may result in enormous economic loss as well as catastrophic environmental disasters. Therefore, it is of significant importance to reasonably assess the structural integrity of subsea pipelines under high-pressure/high-temperature service conditions, especially for critical issues such as corrosion fatigue and low-cycle fatigue that are highly likely to occur. Engineering critical assessment has been widely adopted in industries for structural integrity assessment. However, the cracking and fatigue processes in the cases of corrosion fatigue and low-cycle fatigue are complicated, involving both mechanical and environmental factors. Current industrial standards for engineering critical assessment only provide limited guidance in particular for corrosion fatigue. Low-cycle fatigue is even out of their scopes. So there exists controversy about the applicability and hence the results of the current industrial standards when conducting engineering critical assessments for subsea pipelines serving high-pressure/high-temperature reservoirs. Based on these facts, the author in this research developed an engineering critical assessment approach in particular for corrosion fatigue and established a model for predicting the crack growth under low-cycle fatigue loads. Applications have been made. Comparisons with the experimental data showed that the proposed engineering critical assessment approach and fatigue crack growth model can reasonably assess the structural integrity of subsea pipelines under high-pressure/high-temperature service conditions.