PSI - Issue 77

Jan Kec et al. / Procedia Structural Integrity 77 (2026) 264–271

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1. Introduction Hydrogen is anticipated to play a key role as a storage medium for surplus electricity generated by solar or wind power plants. To facilitate its distribution, hydrogen can be blended with natural gas and transported via existing pipeline networks to end-users or stored to meet future energy demands. However, a significant challenge arises from hydrogen's tendency to cause embrittlement in steel, leading to reduced ductility, lower FT, and an accelerated FCGR. The suitability of steels for hydrogen transport is verified in accordance with ASME B31.12 by testing FT and FCGR in gaseous hydrogen. These tests require special test equipment which is expensive and the whole process is therefore very costly and time consuming and requires structural safety regulations. Electrochemical hydrogen charging appears to be an alternative method to testing in gaseous hydrogen, as it does not require such complex testing equipment. Alvaro et al. (2019) studied the effect of electrochemical hydrogen charging in a 0.1 M Na 2 SO 4 electrolyte at constant potential of −14001 mV SCE on Fe-3wt% Si ferritic steel and X70 steel at different load asymmetries (R = 0.1 and R = 0.5) and different frequencies (f = 0.1 Hz, f = 1 Hz, f = 10 Hz). The results show an increase in FCGR in all test cases, but the largest increase in FCGR was observed at the lowest frequency and vice versa. In the case of electrolytic charging of Fe-3wt%Si steel, the acceleration was up to 1000 times, and in the case of X70 steel, the acceleration was 76 times compared to FCGR in air. Fractographic analysis revealed a change in fracture mechanism from transgranular to quasi-cleavage. António et al. (2025) investigated the effect of electrochemical charging in a 0.5 mol/L H 2 SO 4 + 0.25 g/L As 2 O 3 electrolyte on tensile mechanical properties and fatigue behavior of 316L austenitic steel and TIG welded joints in a three-point bend (3PB) test at R = 0.1 and a frequency of f = 10 Hz. It was found that the ductility decreased by 13 % in the welded joint due to the effect of hydrogen, and the fatigue strength at half a million cycles was reduced by 6 %. Donnerbauer et al. (2025) characterized the fatigue behavior of ASI 4140 steel in two heat-treated conditions (high strength and low-strength conditions) in a 3.5 wt.% NaCl electrolyte at R = 0.1 and a frequency of f = 10 Hz. Their results indicate that fatigue life reduced. However, only in the high-strength condition did the fracture mechanism change to intergranular. M. F. W. Chowdhury et al. (2024) evaluated the fracture toughness of X65 steel on (3PB) specimens subjected to electrochemical charging in a 0.1 M NaOH electrolyte at 9 mA.cm -2 , equivalent to testing in gaseous hydrogen at a pressure of 200 bar. The main conclusion of the study was that both air testing and electrolytic charging resulted in stable crack growth. The fracture toughness values were significantly lower than those obtained in air. Fractographic analysis revealed that the material exhibited significant ductility under electrochemical charging corresponding to hydrogen-assisted plastic fracture. M. Cauwles et al. (2022) investigated the effect of electrochemical pre-charging of X70 steel on Charpy V-notch (CVN) impact toughness at temperatures between -80 °C and +20 °C. The pre-charging was performed in 0.5 M H 2 SO 4 electrolyte with thiourea (CH 4 N 2 S) at a constant current density of 0.8 mA/cm -2 . The most noticeable decrease in CVN impact toughness occurred at the highest test temperature (around 16 %). The effect of hydrogen appears to decrease with decreasing temperature, and thus the lowest effect was observed at the lowest temperature. Fractographic analysis suggested that hydrogen caused delamination during fracture, thereby reducing the absorbed energy. P. Tian et al (2018) measured the tensile strength, impact toughness, and fatigue properties of a pipe body and weld joint of a high-frequency welded (HFW) X70. The HFW weld was the weakest spot from a fatigue point of view, therefore this type of weld was selected for FT and FCGR testing under the influence of electrochemically charged hydrogen.

Nomenclature FT Fracture toughness FCGR Fatigue crack growth rate 3PB Three-point bend CVN Charpy V-notch HFW High-frequency welded R t0.5

Yield strength at 0.5 % total strain

R m

Tensile strength