Title : Pipeline integrity challenges across offshore fields: The 6 gas lift pipeline case study
Abstract:
This paper presents a detailed pipeline integrity investigation of a 6” subsea gas lift pipeline that experienced premature leakage shortly after commissioning. The objective is to identify the underlying damage mechanism, establish the immediate, direct, and root causes of failure, and derive integrity focused recommendations to prevent recurrence in similar pipeline systems. The scope covers design, material selection, installation, commissioning, preservation, and early operational phases, with particular emphasis on integrity risks associated with residual stresses, environmental exposure, and material susceptibility. A structured Root Cause Analysis (RCA) was conducted using a Barrier-Based Systematic Cause Analysis Technique (BSCAT), integrating engineering review, inspection data, laboratory testing, and operational history. The investigation included subsea surveys, pipeline retrieval, non-destructive testing (MPI, PAUT), destructive examination, metallography, SEM/EDS, XRD, hardness profiling, and mechanical testing. Design documentation, installation records, hydrotesting and drying procedures, and operating data were reviewed to assess barrier effectiveness across the pipeline lifecycle.
The investigation concluded that the pipeline failure was caused by sulfide stress cracking (SSC), driven by the simultaneous presence of material susceptibility, a corrosive internal environment, and longitudinal tensile stresses. Although the pipeline steel complied with API 5L and NACE requirements, laboratory findings revealed localized hardness exceeding SSC thresholds and microstructural features that increased hydrogen cracking susceptibility. Residual seawater following hydrotesting, combined with H₂S/CO₂ in the lift gas, created conditions favourable for hydrogen generation and absorption, while longitudinal stresses were most likely introduced during pipelaying or global buckling. Key recommendations include enhanced post-hydrotest drying practices, improved verification of SSC resistance testing, review of pipelaying and clamping procedures to minimize residual stresses and strengthened integrity barriers during commissioning and early operation.
This case study provides a rare and a focused integrity perspective on how latent construction- and commissioning related factors can rapidly compromise pipeline integrity despite short operational exposure. It highlights the limitations of conventional SSC qualification testing when not supported by detailed metallurgical validation and demonstrates the importance of viewing pipeline integrity as a lifecycle system rather than a design-only compliance exercise. The findings offer transferable lessons for gas lift and sour service pipelines, particularly in offshore developments where drying efficiency, stress management, and early-life integrity assurance are critical.
