Objective Vibration-induced fatigue failures in compressor inlet and outlet pipe girth welds have become increasingly prominent and pose a critical threat to the safe operation of natural gas compressor station pipelines. Current remaining-life assessment methods for girth welds with crack defects provide only theoretical frameworks, lacking calibrated parameters tailored to complex loads and specific materials. In particular, a scarcity of systematic crack-growth rate data under combined pressure-vibration conditions hinders the accurate prediction of remaining service life for girth welds with microdefects.

Methods A test-based method is proposed to predict the remaining service life of girth welds with microdefects on compressor inlet and outlet pipes. Focusing on these girth welds, an experimental platform capable of applying combined alternating-stress-vibration loading is established. Tests are conducted using field-derived parameters, including operational pressures, girth weld joint material specifications, and actual vibration spectral characteristics. Crack-growth magnitudes and corresponding time durations are obtained for X70-WPHY70 grade butt girth welds. Finally, limiting crack depths determined through Fitness-for-Service (FFS) defect assessments are applied to predict the remaining service life of girth welds with cracks.

Results After 504 h of continuous loading under characteristic vibration spectra and fluctuating pressure, crack-growth behavior correlates with vibration acceleration. Remaining service life is extrapolated using the Paris law. At a low acceleration of 2.31 g (where 1 g = 9.8 m/s²), cracks exhibit no growth, leaving service life virtually unaffected. At 3.07 g, cracks begin to propagate, resulting in a predicted remaining service life of 6, 267 h. When acceleration further increases to 6.20 g, crack-growth rates accelerate, reducing the predicted remaining service life to 4, 402 h.

Conclusion The proposed method provides empirical test data and a quantitative framework for assessing safety and predicting the remaining service life of girth welds containing microdefects in compressor inlet and outlet pipes. Furthermore, it offers a benchmark for evaluating the integrity of welded joints subjected to similar complex loading conditions. This approach enhances the intrinsic safety of natural gas compressor station piping systems and effectively mitigates risk from girth weld cracking failures.