Analysis of fracture energy in drop weight tear testing of API X65 gas pipeline steel

In this research, the effect of low velocity impact (LVI) on different components of fracture energy of API X65 gas pipeline steel is investigated using drop weight tear test (DWTT) specimens. For this purpose, twenty one test specimens (arranged in seven similar test groups) were used. The LVI tests were carried out first on six test groups by releasing the machine hammer from different heights from 0.05 m to 0.3 m. Then, full fracture DWTTs were conducted on all seven test groups using 2 m drop height. The fracture energy of tested specimens and its different components were calculated from test data using an instrumented hammer. These were compared to similar energies of virgin test specimens. It was found that by increasing LVI energy, yield energy increased up to 26% due to work hardening. However, crack initiation energy decreased significantly (down to 48%) due to plastic deformation at crack tip and crack tip blunting. By considering energy consumption, a novel test technique was presented for exact determination of crack initiation point.