Fatigue life prediction for an API 5L X42 natural gas pipeline

• Fatigue tests were performed with three kinds of specimens, including ASTM specimen.
• The notch effect was lower for the 25% wall-thinned specimen than for other specimens.
• Stress concentration factors and fatigue notch factors were obtained for an API 5L X42 line pipe.
• The predicted S–N curves have good agreement with fatigue test data.

Gas pipelines are exposed to a fatigue load related to both the ground and cars because of being buried at a depth of 1.5 m. Gas pipeline integrity is of considerable importance because earthquake-induced damage of gas pipelines can lead to gas leaks and fire, resulting in property damage and endangering lives. For these reasons, evaluation of the mechanical properties of gas pipelines must be performed. Therefore, in this study, the fatigue behavior of an API 5L X42 gas pipeline was estimated. ASTM standard specimens, curved plate specimens, and wall-thinning curved plate specimens were collected from the API 5L X42 gas pipeline, and fatigue testing was subsequently performed. Also, the S–N curves of each specimen were estimated, and then predicted by theoretical methods according to the depth of wall-thinning. Finally, it was verified that the predicted models were in good agreement with actual test data.