PSI - Issue 82

A.H. Jabbari Mostahsan et al. / Procedia Structural Integrity 82 (2026) 169–173 A. H. Jabbari Mostahsan et al. / Structural Integrity Procedia 00 (2026) 000–000

171

3

The wedge-loaded CT specimens were stored for 1000 h in pure hydrogen gas at the pressure of 200 bar and at room temperature. Before and after charging the specimens with hydrogen, the crack length of each specimen was measured using a Keyence VHX-6000 digital microscope. After charging, the actual stress intensity factor was re calculated using an experimentally determined lift-off curve according to the ANSI/NACE TM0177 (2016) standard and a numerically calculated correction factor as introduced by Jabbari et al. (2026). The hydrogen-charged specimens were immersed into liquid nitrogen for a few minutes, and the cold specimens were then fractured using a TRUMPF TruBend 7036 electro-mechanical bending machine. Finally, the fracture surfaces of the specimens were investigated using a TESCAN MIRA3 SEM to detect any potential signs of HAC. 3. Results and discussion 3.1. Microstructure Fig. 2 illustrates the microstructure of the P460QL steel. The micrographs and the inverse pole figure (IPF) maps captured in three different directions (TS, LT and LS) show an almost isotropic ferritic microstructure, which contains cementite precipitates at the grain boundaries but also inside the grains.

Fig. 2. Light-optical micrographs (left) and merged EBSD-IPF maps (right) showing the microstructure of the P460QL steel in longitudinal-transverse (LT), transverse-short transverse (TS) and longitudinal-short transverse (LS) directions.

3.2. Hydrogen-assisted cracking None of the three investigated CT specimens showed any macroscopic signs of HAC, since the crack lengths measured before and after hydrogen charging were equal, as exemplarily illustrated in Fig. 3. The re-calculated actual stress intensity factors of the three CT specimens were in the range of 65-67 MPam 0.5 , which were very close to the desired stress intensity factor of 66 MPam 0.5 . Hence, according to the ISO 11114-4 (2017) standard the P460QL steel is qualified up to its ultimate tensile strength for manufacturing cylinders that can be used at room temperature and at the pressure of 200 bar for storing hydrogen and hydrogen-bearing gases with volumes up to 3000 liters. However, since the 13 mm-thick specimens did not fulfil the requirements of plane strain conditions, this result is valid for cylinders with the maximum wall thickness of 13 mm. However, determining the threshold stress intensity factor of the P460QL steel requires further testing of specimens that are loaded even at higher stress intensities.