There are many advantages to introducing hydrogen into the gas grid, especially for industry, domestic heat and heavy-duty transport applications. On site, small scale hydrogen production is costly and transporting hydrogen in tankers to fuel filling stations is highly inefficient. Hydrogen as a key element of achieving net zero is now being taken very seriously with major projects in the UK and around the world. The use of hydrogen in converted natural gas pipelines, especially at high percentage levels is relatively untried from the perspective of long-term pipeline integrity. There is a risk of pipeline life being adversely affected by hydrogen embrittlement. The extent of this risk requires quantification before repurposing can be implemented.

The work presented includes pressure cycling trials with 30% hydrogen rich methane gas mixes using full scale 300mm diameter pipe in a 6m loop configuration. The pressure cycling regime of 45-70bar was derived from historical records of pressure fluctuations in the UK gas transmission grid managed by National Grid and attempted to accelerate 50 years of pressure cycles in a six-month test period. Two types of pipeline were included in the trial consisting of X52 carbon steel pipe with girth welds and MASiP, a new type of polymer lined pipe reinforced with high strength steel strip.

This paper presents project objectives, challenges, results and data after six months exposure, with recommendations for future trials. The results showed no significant changes in the performance of the pipes tested but did show significant changes to the elongation, Charpy and hardness properties of x52 steel test coupons stored within the pipe- but not tensile strength. These results support the view that risk mitigation should include quantitative fatigue life evaluations with a new hydrogen specific materials data base as an evidential basis for risk evaluations, especially under cyclic stress conditions.