Failure probability analysis of buried steel pipelines under reverse faulting considering resistance reduction

Reverse-fault-induced permanent ground displacement threatens the safe operation of buried pipelines, and resistance degradation of in-service pipelines further increases their failure risk under faulting. Aiming at the difficulty in quantifying resistance degradation in pipeline safety assessment under fault hazards, a reliability analysis framework based on resistance reduction is proposed. A three-dimensional finite element model of buried X80 steel pipe crossing a reverse fault is first established and calibrated against full-scale tests. Considering steel grade, pipe diameter, fault dip angle, diameter-to-thickness ratio and earthquake magnitude in parameterized cases, 1553 effective finite element samples are generated. Maximum hoop stress, equivalent plastic strain, logarithmic strain and displacement are taken as response quantities to construct an SSA-BP surrogate model embeddable in Monte Carlo simulation. The resistance reduction factor RF is introduced into the resistance term of the limit state function; failure is judged by the safety margin between reduced material resistance and surrogate-predicted stress, with explicit propagation of surrogate model residuals. Results show that increasing D/t and decreasing RF significantly raise the failure probability. When RF=1.0, increasing D/t from 36 to 66 raises the failure probability from about 71.9% to about 92.4%; when D/t=66 and RF=0.8, the failure probability approaches 100%. Hoop stress exceedance is suitable as the primary reliability criterion in the parameter space studied, while PEEQ and LE can serve as supplementary indicators for local plasticity and buckling deformation.