European natural gas pipeline operators are faced with future needs to transport hydrogen in their pipeline grids. To use renewable energy more efficient, it can be converted to hydrogen. From the past it is known for natural gas that pipelines are the safest and most economic measures to transport gas to the end users. As pressurised hydrogen might differently interact with cabon steel than natural gas, questions about suitability of carbon steel pipe came up. Near future scenarios set the industry’s focus more on smaller diameters for pure hydrogen pipelines, whilst large diameter pipe is more dedicated to the application for hydrogen blends. As hydrogen quantities are expected to increase, also large diameter pipes might be used later for transporting pure hydrogen and the industry is going to be prepared for this situation.

For this reason, EUROPIPE has set up a program to evaluate the material behavior in pure hydrogen atmospheres and to support operators and designers with the results for their approach to safe pipeline operation. The program comprises investigations in different steels with different grades, chemistries, und microstructures. The focus is set on steels in the strength class between L450 to L485, as the hydrogen performance of those steels is generally considered to be more critical then lower grades.

As ASME B31.12 sets standards for worldwide hydrogen pipeline design and material property requirements, the program also focuses on testing according to this standard to evaluate the toughness level and the crack propagation behavior of carbon steels. This paper discusses the available results of this program and gives an overview about the influence of pressurized hydrogen on critical stress intensity and crack propagation under cyclic loading. The paper discusses also the reliability and significance of the available testing methods.