Risk analysis of injuries caused by accidental ejection of pipeline pigs

To systematically prevent injuries caused by accidental pig ejection during pigging operations, this study examines two typical accidents: a crude oil pipeline incident in an overseas project (2018) and a natural gas pipeline accident in China (2025). Both cases revealed a common cause-incomplete pressure relief. A fault tree model was developed using the Fault Tree Analysis (FTA) method, with"injury due to accidental pig ejection"as the top event. Seventeen basic events were identified, and 40 minimal cut sets were derived through qualitative analysis, clarifying multiple potential accident pathways. Structural importance ranking highlighted two critical factors permeating all accident pathways: inability to determine pig position(X16) and personnel operating directly in front of the pig launcher/receiver(X17). Using the Zhangye Compressor Station of the Second West-East Gas Pipeline as a case study, quantitative analysis calculated the top event probability at 1.7×10^-3. Results indicated that eccentric wear of pig driving cups (0.31), excessive interference fit (0.23), and unchecked internal leakage (0.23) were primary causes of incomplete pressure relief. Based on these findings, risk control measures were proposed across five dimensions: design and construction, operation and maintenance, standardized procedures, emergency systems, and technological innovation. The field application of two innovative technologies-stress-strain monitoring and laser ranging-was also discussed. This research provides practical guidance for risk prevention and control in pigging operations for oil and gas pipelines.