What are the material requirements for carbon steels used in hydrogen pipeline systems according to Doc 121/14?

Introduction

Doc 121/14 outlines the material requirements for carbon steels used in hydrogen pipeline systems. It provides recommendations based on the strength and hardness properties necessary for safe hydrogen gas transport.

Answer

According to Doc 121/14, carbon steel has been widely used in hydrogen pipeline systems. For pipeline material, carbon steels with low yield stress, such as API 5L X52 (and weaker) and ASTM 106 Gr B steel, are typically associated with this application. These alloys have shown favorable results due to their relatively low strength. The guideline suggests using API 5L PSL 2 pipe steel with a maximum grade of X52 for hydrogen pipeline systems. The low-stress design employed to prevent third-party damage to the pipelines also reduces the potential for hydrogen damage. It is recommended to normalize the carbon steel for hydrogen service to ensure the presence of fine-grained homogenous microstructures. Special attention should be given to the surface condition of alloy mill forms during and after treatment. Regarding chemical compositions, conventional carbon steel metallurgy compositions have been found suitable for hydrogen pipeline applications. Newer melting processes that reduce sulfur and phosphorus can be considered for severe applications. Weldability should be maintained, and the maximum carbon equivalent for hydrogen systems is recommended to be 0.43. Regardless of alloy selection, it is advisable to select the lowest possible tensile strength consistent with the application. For pressures exceeding 50 bar, the guideline highly recommends considering toughness requirements for certain steel mill forms used in hydrogen pipeline applications, as specified in Pipeline Design and Construction.