Notes on the Development of the Hydrogen Supplement to IGEM/TD/1

The supplement to the standard IGEM/TD/1 gives the additional requirements and qualifications for pipelines transporting hydrogen and hydrogen/natural gas blends (NG/H blends) at pressures at MOP exceeding 7 barg.
Where there is no numbered section in the supplement corresponding to a section in the main document, the requirements of the main document apply in full. Where there is a corresponding numbered section in the main document, the numbered section in the supplement is either in addition to or replaces the section in the main document.
Repurposing in accordance with the recommendations of this supplement should only be considered for pipelines which have been operated in accordance with the recommendations of the main document for at least 5 years, and which have been audited in accordance with the recommendations of clause 12.4.2.1. This requirement is specified so that compliance with the operational and maintenance requirements specified in the main standard is confirmed through records. With respect to pipelines, this includes the requirements for MOP affirmation. This requirement is more onerous than the requirement is ASME B31.12 Clause GR-5.2.1[1], which requires that assessment for conversion to hydrogen service shall be assessed at the time of conversion, and reassessment of integrity shall be done within 5 years of conversion.
NG/H blends containing more than 10% mol hydrogen are considered to be equivalent to 100 mol.% hydrogen with respect to limits on design stresses and the potential effect on the material properties and damage and defect categories and acceptance levels, unless an additional technical evaluation is carried out to qualify the materials (see clause S5.8). It is noted that there is no evidence to confirm that blends containing up to 10 mol.% hydrogen do not cause material degradation, but it is considered that the risk is low.
With respect to industry experience with towns gas, this product contained 10-20 % carbon monoxide, which has been identified as inhibiting the effect of hydrogen on fracture toughness and fatigue crack growth. Therefore, the historical experience with town gas is not relevant.