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

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1. Introduction Although many steels are susceptible to hydrogen embrittlement (HE) and hydrogen-assisted cracking (HAC), steels are still the primary choice for producing vessels and pipelines that are needed for the efficient transmission and distribution of gaseous hydrogen. Ghosh et al. (2018), Li et al. (2022) and Ohaeri et al (2021) summarized that the microstructural characteristics of steels potentially determines hydrogen trapping and, thus, the susceptibility to HE and HAC. As martensite-based high-strength pipeline steels such as API 5L grades X80, X100 and X120 are rather susceptible, ferrite-based medium-strength pipeline steels such as grades X65 and X70 are preferred for manufacturing components that are in contact with hydrogen for applications at moderate gas pressure. As reviewed by Rahimi et al. (2025), the effect of hydrogen on the properties of pipeline steels has been extensively investigated under both electrochemical and gaseous charging conditions. In particular, gas charging of specimens under controlled pressure and temperature is beneficial for investigating HE and HAC of steels that are exposed to pure or blended hydrogen gas during service. Even under conditions that are difficult to simulate in experiments, the response of grades X65 (L450) and X70 (L485) to hydrogen was investigated using numerical approaches, as exemplarily demonstrated by Drexler et al. (2022, 2025). Ghosh et al. (2018) concluded that controlling nonmetallic inclusions and homogenizing the microstructure are most important for reducing irreversible hydrogen traps and, thus, for improving the resistance of steel against HAC. In particular, micro-alloyed steels that have manifold industrial applications meet these microstructural requirements. Hence, this work investigates the susceptibility of the P460QL micro-alloyed steel to HAC in order to demonstrate its basic suitability for applications in pure hydrogen gas. 2. Methodology The HAC susceptibility of hot-rolled and tempered P460QL micro-alloyed steel (0.086 wt.% C, 1.55 wt.% Mn, 0.47 wt.% Ni, 0.379 wt.% Si, 0.221 wt.% Mo, < 0.1 wt.% V+Nb+Ti) was experimentally investigated. Six cubic specimens with dimensions of 20 mm × 20 mm × 30 mm for microstructure analysis and three 13 mm-thick compact tension (CT) specimens for fracture mechanics tests as proposed by Jabbari et al. (2025) were wire-cut from the as received 53 mm-thick steel plates. Light optical microscopy (LOM) and scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) were employed for microstructure analysis. The EBSD measurements were performed using a JEOL JSM-7800F field emission scanning electron microscope (FESEM) equipped with an Oxford Instruments Symmetry EBSD detector. In order to produce the obligatory fatigue pre-crack at the notch of the CT specimens, each specimen as shown in Fig. 1 was subjected to cyclic tensile loading at the stress ratio of 0.1 using an Instron ElectroPuls E10000 testing machine. The pre-cracked specimens were loaded according to the constant displacement method using a wire-cut double-tapered steel wedge as shown in Fig. 1. The stress intensity factor of 66 MPam 0.5 applied at the tip of the pre crack was calculated as proposed in the ISO 11114-4 (2017) standard based on the steel’s ultimate tensile strength of 698 MPa. The thickness of the wedge required for achieving this stress intensity factor was numerically determined using the ABAQUS FEA software.

Fig. 1. Double-tapered wedge and CT specimen without pre-crack.