Ductile-to-brittle transition behavior and determination method in X80 pipeline girth welds utilizing the master curve method

The fracture toughness distribution of X80 high-strength pipeline steel girth welds in the ductile-to-brittle transition region was systematically studied using the master curve method. According to ASTM E1921-97 Standard Test Method for Determination of Reference Temperature T₀, for Ferritic Steels in the Transition Range by American Society for Testing and Materials (ASTM), fracture toughness tests were conducted at various temperatures, and the fracture toughness prediction curves at the reference temperature (T₀) and different failure probabilities were determined using the multi-temperature method. Charpy impact energy was converted to fracture toughness at corresponding temperatures using empirical formulas, and the results were compared with direct test data. To validate the effectiveness of the method, 198 pieces of fracture toughness data from pipeline projects were analyzed, and T₀ was calculated using the single-temperature method. The results show that the T₀ value determined by the single-temperature method has good consistency with the test results, fully demonstrating the effectiveness and applicability of the main curve method in describing the ductile-to-brittle transition behavior of X80 pipeline girth welds. This research provides a theoretical basis for the assessment of fracture toughness of high-strength pipeline steel, as well as reliable methodological support for pipeline integrity evaluation in engineering practice.