Computational Predictions of Permeability, Diffusivity & Welding Integrity in Hydrogen Pipelines
Authors: Elsebeiy O. M. 
Published: October 2024

Abstract
Hydrogen is an important energy carrier and a clean substitute for natural gas that has the potential to support increased use of carbon-free or renewable energy in the global energy markets. It is non-corrosive, tasteless, colorless, odorless, and non-toxic. Hydrogen is highly flammable; it is difficult to keep from leaking. In the same way natural gas is transported today, Hydrogen can be transported too through pipelines and using existing pipeline infrastructure may be a particularly cost-effective solution to delivering hydrogen in large volumes, generally repurposing part of the 1.3 million Km installed natural gas pipeline around the world for hydrogen transportation could slash the cost by 50-70% compared to building new hydrogen pipeline infrastructure. However, there are some doubts about the use of the current pipeline infrastructure in the hydrogen transportation sector because hydrogen can degrade the mechanical properties of most metals when a steel pipeline is used to transport hydrogen, hydrogen atoms are absorbed into the steel which leads to accelerated rates of fatigue crack growth, reduces the fracture resistance, strength and ductility, in general, we can say it can embrittle metals. Hydrogen embrittlement (HE) affects the integrity and performance of steel pipelines, particularly in hydrogen-rich environments. This process involves the absorption of hydrogen into the steel matrix, as hydrogen permeates the steel, it can diffuse to regions of high stress, where it may accumulate, reaching critical amounts forming brittle hydrides or creating voids and when stress is applied to the embrittled object ultimately it could lead to crack initiation and propagation, or we can say leading to disastrous consequences. In General, the Absorbed amount of hydrogen and material microstructure determines the hydrogen embrittlement level and depending on the metal's capability, crack failure may take a long time or may occur instantaneously. In addition, Hydrogen embrittlement (HE) could also affect the pipeline's mechanical properties by reducing the maximum operational pressures leading to potential pipeline rupture.
To investigate the suitability of the steel pipeline materials with hydrogen, A 3D FE model simulation was established on an underground natural gas pipeline with different Grades using commercial analysis software to investigate the effect of many parameters on hydrogen embrittlement (HE) and the acceptable limit to transport hydrogen in the existing pipeline infrastructure without causing any damage for the pipeline or the weld structural integrity so that the pipeline system continues to operate under a safe condition within its design lifetime taking into consideration the blending percentage used worldwide. Then we extended our simulation to become more reliable focusing not only on the base material but also on the welding area so we combined the welding process with diffusion and failure (embrittlement) simulation to predict failures in hydrogen welded pipelines instead of the seamless pipelines as they are widely used in the natural gas transported pipeline.