Risk-based maintenance time for oil and gas steel pipelines under corrosion including uncertainty on the corrosion rate and consequence-based target reliability

A risk-based procedure is proposed to recommend a sustainable maintenance strategy for oil and gas steel pipelines under internal pitting corrosion. The procedure considers the uncertainty and evolution on time of the corrosion depth, which depends on the initial depth and the corrosion rate, and includes the calculation of the time variant failure probability, or reliability, and its acceptable limit (target) which are calculated according to the importance of the pipeline failure consequences. Inspection results from pig runs, on an actual pipeline, are the basis to calculate the pipeline failure probability on segments of 20 km length. These calculations are per-formed via Monte Carlo simulation and the time variant reliability index is compared to the target reliability index per segment and per importance level. The optimal time is the time when the reliability index meets the target reliability for the considered level of failure consequences. The results allow for the priorization on the attention or pipeline segments, and funds allocation, for pipelines maintenance works according to the risk exposition conditions of the segments.

Automated summary

A risk-based procedure is proposed for recommending maintenance strategies for oil and gas steel pipelines with internal pitting corrosion. This procedure considers the uncertainty and evolution of corrosion depth over time, and calculates the failure probability and acceptable limit based on the consequences of pipeline failure. Monte Carlo simulation is used to calculate the failure probability for segments of the pipeline based on inspection results from pig runs. The time variant reliability index is compared to the target index to determine the optimal time for maintenance works.