Time-variant system reliability of pitting corroded steel pipelines

This study investigates time-variant reliability of pitting corroded pipelines, focusing on several key factors including stochastic development of corrosion defect dimensions, temporal emergence and spatial distribution of defects, and mechanical interaction between defects under operational (high-pressure) and non-operational (low/zero-pressure) conditions. Multiple failure modes are assessed through Monte Carlo simulations with 10,000 samples. Under the operational condition, the probability of failure is calculated for events corresponding to 'small leak by burst' and 'large leak by burst'. For the non-operational condition, 'small leak by wall perforation' is the only relevant failure mode. Results indicate that in the operational condition, 'large leak by burst' is likely the dominant failure mode during the early years of operation. However, as the probability of failure increases over time, 'small leak by burst' becomes the dominant mode. The probability of wall perforation reaches the same level as 'small leak by burst' after only a time lag of a couple of years. This suggests that for the assumed conditions and a target annual failure probability of 10-3 (low safety class) or higher, accounting for bursting failure may be unnecessary, and wall perforation assessment could suffice. For lower target annual failure probabilities, bursting failure may become critical.