Technical status and considerations of brittle fracture control of pipe fittings

The station temperature of China-Russia Eastern Gas Pipeline Project is designed low to －45 ℃, which poses new challenges to the brittle fracture prevention capability of pipeline facilities, so it is necessary to set up scientific and reasonable toughness index requirements to prevent brittle fracture of in-service components under low temperature conditions. The development process of brittle fracture control technology, from empirical method to fracture analysis diagram method and then to fracture mechanics method, was systematically described. The empirial method based technical status on brittle fracture control of oil and gas pipelines was analyzed with China-Russia Eastern Gas Pipeline as the example. Meanwhile, through the comparison and analysis with the brittle fracture control requirements in ASME Boiling and Pressure Vessel Code (BPVC), the deficiencies of brittle fracture control measures for oil and gas pipeline fittings were pointed out. Analysis shows that the experience-based Charpy impact toughness index may be insufficient to prevent brittle fracture when applied to high toughness pipeline steel. Therefore, it is suggested to ① build a perfect fracture mechanicsbased brittle fracture control index system for high-grade high-toughness pipeline steel, ② add Nil-Ductility Transition (NDT) test requirements based on the existing brittle fracture control indexes, ③ and establish brittle fracture control requirements based on fracture mechanics evaluation.