Structural integrity assessment for deep-water subsea pipelines

Deep-water subsea pipelines often have to face highly challenging service conditions such as high pressure/high temperature (HP/HT). Structural integrity assessments accounting for corrosion fatigue (CF) and low-cycle fatigue (LCF) therefore are crucial from the perspective of structural safety and cost efficiency. In this paper, engineering critical assessment (ECA) and structural integrity issues of subsea pipelines associated with the HP/ HT service conditions are discussed and a new specified ECA scheme is developed. The development includes two parts. In the first part, CF is addressed in 3 levels, i.e., deriving the corrosion-crack correlation model for hydrogen embrittlement (HE) influenced subcritical fatigue crack growth (SFCG), establishing the synthetic SFCG model for CF and finally utilizing the transition stress intensity factor (SIF) for achieving reasonable assessments of CF in seawater. In the second part, 2 levels of work related to LCF is performed, i.e., building up the energy principles based SFCG model for high-cycle fatigue (HCF) and adapting it to LCF. In each subpart, advancement in relevant studies is reviewed with reference to current industrial codes. The work is examined and its effectiveness is demonstrated with applications.