CVN and DWTT Energy Methods for Determining Fracture Arrest Toughness of High Strength Pipeline Steels

Battelle two curve model (BTCM) was developed in the 1970s and successfully used for determining arrest toughness for ductile gas transmission pipelines in terms of Charpy vee-notched (CVN) impact energy. Practice has shown that the BTCM is accurate only for pipeline grades up to X65, but not for high strength pipeline grades X70 and above. Different methods to improve the BTCM were proposed over the years. This paper reviews the BTCM and its modified methods in terms of CVN energy or drop weight tear test (DWTT) energy for determining arrest toughness of ductile gas pipeline steels, particularly for high strength pipeline steels X80 and beyond. This includes the often-used Leis correction method, the CSM factor method, Wilkowski DWTT method and others. The CVN and DWTT energy-based methods are evaluated and discussed through the critical analysis and comparison with full-scale experimental data. The objective is to identify reasonable methods to be used for determining the minimum fracture toughness required to arrest a ductile running crack in a modern high strength, high pressure gas pipeline. The results show that available nonlinear models to correlate the standard DWTT and CVN energies are questionable, and the Leis correction method is a viable approach for determining arrest toughness for high strength pipeline steels, but further study is needed for ultra-high pipeline grades. Suggestions for further improving the BTCM are discussed.