Reliability modelling and assessment of subsea oil and gas pipelines considering competing failures caused by dropped object impact and corrosion degradation

Reliability assessment of subsea pipelines is critical for preventing leaks and ensuring operational safety. This study addresses pipelines subjected to concurrent dropped-object impacts and corrosion degradation. By establishing both a competitive-failure reliability model that accounts for failure mode interactions and its corresponding parameter determination methodology, an integrated reliability assessment framework is proposed specifically for subsea pipeline systems under competing failure scenarios. Case studies on DN400 pipelines reveal that traditional single-mode assessments exhibit excessive conservatism, compromising result accuracy. The model demonstrates that ultimate failure stems from temporal competition between failure modes: corrosion dominates late-stage degradation while impacts govern acute structural responses during mid-to-late service phases. Comparative analyses show the competitive- failure model achieves more rational residual life predictions than conventional methods. The framework provides a theoretical basis for optimizing inspection intervals and maintenance strategies, particularly for pipelines in high-risk zones with complex environmental loads. Finally, the proposed methodology was extended to reliability assessment of subsea pipelines with different steel grades and specifications, yielding corresponding reliability analysis results. These findings advance reliability methodologies by reconciling multi-failure physics, offering practical references for design optimization and safety management of subsea energy infrastructure. The model's adaptability shows potential for extension to other marine structures exposed to combined mechanical and environmental stressors.