Time-dependent emitted H₂ content modeling via a reliable diffusion analysis program was performed for H₂-enriched polymers under high pressure. Here, the emitted hydrogen concentration versus elapsed time was obtained at different diffusivities and volume dimensions for cylinder-, sphere- and sheet-shaped specimens. The desorption equilibrium time, defined as the time when the H₂ emission content is nearly saturated, was an essential factor for determining the periodic cyclic testing and high-pressure H₂ exposure effect. The equilibrium time in the desorption process was modeled. The equilibrium time revealed an exponential growth behavior with respect to the squared thickness and the squared diameter of the cylinder--shaped specimen, while it was proportional to the squared diameter for the sphere-shaped specimen and to the squared thickness for the sheet-shaped specimen. Linear relationships between the reciprocal equilibrium time and diffusivity were found for all shaped polymers. The modeling results were confirmed by analysis of the solutions using Fick’s second diffusion law and were consistent with the experimental investigations. Numerical modeling provides a useful tool for predicting the time-dependent emitted H₂ behavior and desorption equilibrium time. With a known diffusivity, a complicated time-dependent emitted H₂ behavior with a multi-exponential form of an infinite series could also be predicted for the three shaped samples using a diffusion analysis program.

The in situ small punch (SP) test method is a simple screening technology developed to assess the hydrogen embrittlement (HE) characteristics of structural steels. This method can easily adjust the influencing parameters such as test temperature, gas pressure, and punch velocity depending on the hydrogen service environment. With increased hydrogen consumption, using pipelines for mass hydrogen transportation is being considered. This study evaluated the HE susceptibility of API-X52 and API-X70 steels, considering the hydrogen usage environment. The study investigated the effects of hydrogen pressure and punch velocity on the HE behaviors of each pipe steel at room temperature using the SP energy and relative reduction in thickness (RRT) to determine their effect on HE susceptibility quantitatively. The study found that hydrogen pressure produced a different HE effect; the lower the hydrogen pressure, the more HE was relieved. Particularly, when the punch velocity was high, such as 1 mm/min, the HE effect was significantly relaxed. However, when the punch velocity was below 0.01 mm/min, HE occurred even at low hydrogen pressure conditions, meaning hydrogen diffusion within the specimen during the SP testing reached a critical hydrogen concentration to create a brittle fracture. Both pipeline steels showed similar HE behaviors under a wide range of H₂ pressures and punch velocities, showing an inverse S-curve for quantitative factors of SP energy and RRT against the H₂ pressure at 1.0 mm/min punch velocity. The study classified the observed HE behaviors into four types based on quantitative and qualitative aspects. These findings confirm that the in situ SP test is a useful screening technique, and the factor RRT can be effectively applied to the HE screening of pipeline steels in low and high-pressure hydrogen environments.

Most pipeline steels composed by the ferritic structure are extremely sensitive to the various forms of environmental attack such as stress corrosion cracking or hydrogen environmental embrittlement. Service experience has shown that the application of welds often contains some potential of hazards of cracks and failures. In this study, a series of fracture toughness and fatigue

The tensile properties and hydrogen embrittlement of 304 and 316 stainless steels with various amount and size of grain boundary carbides were evaluated using slow strain rate test (SSRT) and thermal desorption analysis (TDA). The samples were thermally charged with hydrogen at a conditions of high-pressure 10 MPa hydrogen gas at 300 Celsius degree for a sufficient time to saturate