Generally, the design of a pipeline system need to follow rules and regulations, among other to provide a framework for authorities to provide the construction permits. One of the challenges for hydrogen pipeline projects in Europe is that there are currently no harmonized standards available. The paper addresses several aspects of the design of hydrogen pipelines, among other process and safety considerations, material aspects but as well welding considerations.

Related to process considerations first adequate design gas velocities for hydrogen will be discussed. The ignition and combustion properties are very different to Natural Gas. In this respect emergency blow down and heat radiation calculations will be presented and it will be discussed whether the technical solutions for pipeline vent stacks are indeed similar to the solutions known from Natural Gas.

Adequate material selection and the definition of the welding process are relevant to ensure resistance to stress corrosion cracking and hydrogen embrittlement. Generally, the risk of failure is increased at higher temperatures and pressures and is mitigated by low stress levels. Material selection, fabrication processes, design and material thicknesses should be chosen with a view towards achieving low residual stresses. Solutions from ongoing projects will be presented.

Specifically the welding process for hydrogen pipeline is extremely critical. It is important that hardness levels in the weld and the weld heat affected zone are controlled to avoid hard spots. Relevant aspects of a welding specification for construction of a hydrogen pipeline will be presented in the paper. In this respect weld filler metals, weld process qualification, weld operator qualification, mechanical tests, metallographic techniques and NDT techniques will be addressed. Last not least it will be discussed to what extent ECA may be used as a tool to define the limits of acceptance for crack-like defects due to workmanship during welding.