PSI - Issue 54

Daria Pałgan et al. / Procedia Structural Integrity 54 (2024) 322 –331

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Daria Pałgan et al./ Structural Integrity Procedia 00 (2023) 000 – 000

1. Introduction The demand to evaluate the susceptibility of steels to hydrogen embrittlement (HE) in high pressure gaseous hydrogen (H 2 ) environment is rapidly increasing. This is because of the foreseen potential that H 2 technologies would contribute to reaching the goal of a fossil-free society (Rasul et al., 2022). A selection of applications promoting this are replacing coal with H 2 in iron ore reduction, used as fuel in some types of fuel cells, replacing natural gas in gas turbines etc. (Fan et al., 2021; Liu et al., 2021; Öberg et al., 2022). Storage and transportation of H 2 are also crucial for this transition (Hren et al., 2023). It is well known that steels are susceptible to hydrogen which manifests through failure known as HE (Barrera et al., 2018). More in depth understanding on how and how much hydrogen is introduced into steels is crucial to mitigate HE (Djukic et al., 2016) and reveal which HE mechanisms are operating and relevant (Djukic et al., 2019; Lee et al., 2023; Wasim et al., 2021). To design and build H 2 safe infrastructures, knowledge of the quantity and distribution of “ trapped ” hydrogen in steels is required. To achieve this, it is necessary to do systematic studies involving exposure of steel samples in pressurized H 2 environment followed by hydrogen analysis and its quantification. ISO 16573-1:2020 outlines four distinct hydrogen charging methods: cathodic charging, hydrogen absorption in aqueous solutions, hydrogen absorption in atmospheric corrosion environments, and hydrogen absorption in high-pressure hydrogen gas i.e., gaseous charging (ISO 16573-1, 2020). Among these, cathodic charging and gaseous charging have emerged as prominent techniques for laboratory testing conditions. Presently, the literature includes only a few reports that directly compare these two charging methods in terms of their efficiency in inducing hydrogen uptake in steels (Brass & Chêne, 2006; Enomoto et al., 2014). These reports are considering austenitic stainless steels and no similar reports were found for low alloy carbon steels. Brass and Chêne measured the total hydrogen uptake using melt extraction in 316L after charging using various cathodic and gaseous parameters including different electrolytes, cathodic current densities in a wide temperature interval (25-600 °C) and charging time ranges (5-216 hours) (Brass & Chêne, 2006). From (Brass & Chêne, 2006) one can establish a relationship between the hydrogen uptake measured and the respective charging method, however no knowledge about the hydrogen distribution i.e., “trapping” in the steel can be derived. Enomoto et al. have studied the effect of deformation on hydrogen uptake in 304L and 316L steels after charging using cathodic and gaseous methods (Enomoto et al., 2014). Their work shows that both the type of steel as well as the level of deformation can affect the hydrogen uptake and trapping in the steels. Several studies investigated hydrogen trapping mechanisms, unravelling their influence on hydrogen uptake, and ultimately assessing their repercussions on material properties (Bai et al., 2023; Pérez Escobar et al., 2012; Silverstein & Eliezer, 2017; Tsuchida, 2014; Turnbull, 2015; Yaktiti et al., 2022). Hence, a significant knowledge gap persists, particularly concerning the comparison of the effectiveness of cathodic and gaseous hydrogen charging methods in generating similar quantities of absorbed hydrogen as well as hydrogen “trapping” in reversible and irreversible trapping sites. Notably, reversible “diffusible” hydrogen, recognized as the primary culprit of HE, remains of utmost concern, but as the irreversible “trapped” hydrogen might serve as hydrogen source in certain steels and under certain applications can also be considered as potential risk for, HE (Li et al., 2020). Consequently, the need arises to delve deeper into the effects of various charging parameters, critically evaluating their impact on both hydrogen uptake and the resultant mechanical performance of steels (Zafra et al., 2023). In this context, this study focuses on two primary hydrogen charging methods: cathodic charging and gaseous charging and aims to contribute into revealing on their impact on hydrogen uptake and trapping in steels and as well its consequences and determining whether similar hydrogen content and comparable trapping of hydrogen can be obtained using either charging method. Time and temperature are parameters shared for both charging methods. The cathodic charging parameters were selected as common to be used in numerous reports (Koyama et al., 2013; Sugiyama et al., 2000; Yang et al., 1999; Zhang et al., 2022). For cathodic charging characteristic is effect of cathodic current density (Kazum & Bobby Kannan, 2017) and effect of poison (Ajito et al., 2022; Pérez Escobar et al., 2011). In this work we have put the focus on impact of current density, charging time and temperature of the electrolyte. On the other hand, it is generally known that for gaseous hydrogen charging the important parameters are pressure, temperature, and time (Brass & Chêne, 2006; Mine et al., 2016; San & Somerday, 2012). It should be noted that the selected temperatures for the gaseous hydrogen charging in this work were not selected based on service conditions, but more to allow a systematic study on the hydrogen uptake and trapping in the studied steels. 2. Materials and Methods All investigated steels in this work are commercially available plate materials. Table 1 shows the chemical composition of the steels. The microstructure is shown in Figure 1 and consists of ferritic grains with pearlitic bands