Ollie Burkinshaw, Neil Gallon and Jason Edwards, ROSEN UK, address the challenge of integrity management of hydrogen pipelines.
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limate change is perhaps the biggest global challenge of the 21st century. If the world is to succeed in limiting global temperature increases to below 2˚C, all available solutions must be leveraged and accelerated. Electricity and gas will continue to fulfil complementary roles in the future integrated energy system. Electrification of all industrial and residential energy demand is not feasible, and certain industries cannot be readily electrified. In terms of low-carbon energy supply, hydrogen is a logical means to address these issues, as it is easy to transport and store using a significant proportion of repurposed infrastructure. In the medium-term, it appears inevitable that blue hydrogen – whereby hydrogen is extracted from natural gas, and the carbon dioxide (CO2) is stored to prevent emissions (carbon capture and storage [CCS]) – will play a large role. Longer-term, green hydrogen predominantly generated via electrolysis using renewable energy sources is an effective solution for the storage and transportation of intermittent and excess power, providing flexibility and resilience in our energy supply. Regardless of the colour of the hydrogen, pipelines will be required to transport it. This has been recognised globally with initiatives such as the European Hydrogen Backbone, a growing group of now 29 European gas infrastructure companies targeting a hydrogen transmission network of 39 700 km by 2040, with further growth expected after 2040.1 The capital cost of repurposing existing pipelines is expected to be between 10 – 25% of the cost of building new pipelines. For hydrogen pipeline infrastructure (either with 100% hydrogen or a blend of hydrogen and natural gas) to be economically feasible, a significant proportion of the existing global pipeline infrastructure (of which there are several million kilometres) must be leveraged to form the future hydrogen pipeline infrastructure. The European Hydrogen Backbone currently projects that approximately 70% of future hydrogen pipelines will be repurposed existing pipelines.
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The challenge
While the concept of hydrogen pipelines is not new or inherently impossible – there are already thousands of kilometres of hydrogen pipelines in service – the introduction of hydrogen into existing natural gas transmission and distribution networks creates unique challenges. The challenges associated with converting existing pipelines can be summarised in two simple questions for pipeline operators: � Can my existing pipeline be safely converted to hydrogen service? � How can the integrity of a hydrogen pipeline be managed? Apart from the general integrity challenges and threats to any pipeline, the integrity challenges and damage mechanisms specific to hydrogen transport can be split into two main areas. Hydrogen can cause cracking directly (hydrogen-induced cracking), though this is generally not likely from gaseous hydrogen exposure alone and would require high concentrations of hydrogen typically resulting from sour service conditions or cathodic over-protection. More relevant for gaseous hydrogen service, however, is the more insidious influence of hydrogen negatively affecting the material properties of steel line pipe. The most important mechanical properties of steel line pipe are strength (yield strength and ultimate tensile strength), ductility, fracture toughness, and resistance to fatigue cracking. The effect of hydrogen on these properties are summarised in Table 1. The figures in Table 1, which are supported by literature and industry testing, show a wide range of hydrogen-related effects on the different material properties, with varying degrees of severity. Although this wide range is partially accounted for by the different test protocols, hydrogen concentrations, and temperatures used in the studies, it is also largely a function of the very significant variation in how different materials respond to the presence of hydrogen. Line pipe in existing pipeline infrastructure can be up to 100 years old, with the majority in the US and Europe having been installed between 30 – 50 years ago.
