An Updated Fracture Resistance Dataset of Pipeline Ductile Fracture Propagation Based on High Speed DWTT Tests

Abstract

One of the major research topics in the area of gas pipeline fracture control is the suitability of using Charpy energy for ductile fracture control for modern and/or high strength line pipes. A common understanding is that, for pipe body crack self-arresting, the deviation of the actual required Charpy energy from those predicted using the traditional procedure of Battelle Two-Curve Method (TCM) is getting larger with higher strength pipes. DWTT is being paid more attention to because of its larger and full thickness specimen that can better capture the fracture process than a Charpy specimen does. Previous work at TransCanada indicated that various fracture speeds can be achieved in DWTT specimens and it is the steady-state fracture speed that is representative to the actual fracture propagation in a gas pipeline. It has also been found that the steady-state fracture toughness, in terms of either fracture energy or CTOA, is fracture speed dependent with lower fracture toughness for higher fracture speeds. Previous analysis also indicated by considering the speed dependent toughness, better predictions can be obtained for both self-arresting fracture toughness requirement and the fracture propagation speed. Previous DWTT fracture toughness data published by the authors exhibited a strong speed dependence and it was demonstrated that if the actual speed dependence is plugged into the modified TCM, both the fracture toughness and fracture speed would be over predicted. The assumption was that the original TCM was calibrated using pipe fracture data that also had speed dependent fracture toughness but the speed dependence was less strong than those for the modern pipes. This paper presents an updated DWTT fracture dataset that expands the previously published data by adding high speed DWTT test results of modern line pipe steels with a range of grades X70-X100 and three old vintage pipe materials that is representative to the pipes that were used for the original TCM testing and calibration. The toughness data for the low grade pipes also shows speed dependence which purports the previous assumption.