The mechanics of the new hydrogen economy
New announcements for hydrogen projects around the world are coming almost daily, with Australia leading the charge thanks to its abundant solar, wind and real estate resources. Integrity Engineering Solutions Principal Engineer and Managing Director Warren Brown writes.
At the moment, most of the projects are still in the pre-engineering stage and consideration of the actual mechanics of how they are to be executed is perhaps poorly defined. There is a mix of excitement and trepidation, with the speed of development tempered by the worry that their project may end up being the process plant equivalent of the Hindenburg.
While that certainly is possible, given the wrong design, construction or particular set of circumstances, it is worthwhile remembering that hydrogen has been transmitted and stored in pipelines, piping and pressure vessels for decades. Experience from the refining and aerospace industries can be drawn from to demonstrate that, with due care, hydrogen does not represent a particularly extraordinary challenge.
It is this exact experience, including being a world-leader in pressure boundary bolted joints, that has led to Integrity Engineering Solutions performing consulting work on the mechanical, material and welding considerations for a number of Australian and international projects in the Hydrogen sector. Our work has included assessment of materials selection, mechanical design, and hydrogen storage solutions for both ultra-high temperature hydrogen production processes and renewable energy driven hydrogen production and processing plants.
As a result of these projects, it was our finding that, as long as certain situations are avoided (for example HTHA, High Temperature Hydrogen Attack), then the risk profile of hydrogen is very similar to other hydrocarbons. Due to hydrogen’s low density and ease of ignition, it is demonstrable using industry standards that there is very little difference with respect to consequence by comparison to other hydrocarbons.
From our refining experience, if best practices are followed, then leakage of hydrogen should not represent a higher likelihood than other hydrocarbons in refining and LNG. Therefore, the overall risk profile of hydrogen can be maintained at a level that is similar to current hydrocarbon processes. This, in turn, enables the use of current and known risk analysis, risk management and inspection management procedures from the hydrocarbon sector in the hydrogen sector, which is of great benefit.
Of course, if sub-optimal practices are employed, then the certainty of ignition and high propensity to leak due to the small molecule size can make damage from hydrogen leakage extensive. An example of such leakage is shown in Fig. 1, where the remains of a gasket from a hydrogen service piping joint that leaked and caught fire is shown. It can be seen that there was substantial damage to the gasket, which in turn led to a larger fire, impacting nearby equipment and resulting in the need to replace the fixed equipment in the vicinity of the fire prior to recommissioning the unit.
The cost of such an incident is not only limited to the capital equipment replacement costs, or the lost production, but also the possibility of personnel injury and associated unwanted media attention. It is not improbable that a small series of incidents in the first hydrogen plants in global operation may act to severely limit the future of hydrogen as an alternative fuel. This is abundantly apparent with the reporting of the fire incident on January 25, 2022 aboard the Suiso Frontier, which was described in the media as ranging from a “small flame” to a “serious incident”.
It is not hard to imagine that, had the incident involved an actual significant fire, the future of the hydrogen industry would have been adversely impacted. So, it is important that the engineering and construction industry concentrate on getting it right with hydrogen projects.
In most cases, current design and construction practices, particularly with respect to pipelines, will need to be revised to become hydrogen friendly. This is primarily due to the detrimental effect of hydrogen on the toughness and fatigue life of common materials of construction. Current pipeline construction already requires consideration of fracture toughness and fatigue life, but hydrogen significantly elevates the importance of fatigue and fracture by comparison to hydrocarbons.
The effect of hydrogen is dependent on the actual operating parameters of the system, but an idea of the level of level of impact can be seen in Fig. 2. This shows the Failure Assessment Diagram (FAD) for a 40 mm thick SA516-70N pressure vessel with a 138 MPa cyclic stress applied daily, with a crack propagating from a relatively small 2 mm deep x 12mm long initial imperfection. The fatigue life for the vessel in non-Hydrogen service is 313 years (i.e.: fatigue life does not control).
The same vessel in hydrogen service, with faster crack propagation rates and lower fracture toughness due to hydrogen embrittlement only has a nine-year life (i.e. severely fatigue limited design). If the cyclic stress is reduced by 25 per cent, then the fatigue life in hydrogen increases to 36 years. So, it is evident from this that consideration of fatigue and fracture are essential for hydrogen service and that allowable stress may be controlled by these considerations, rather than pressure stress.
In addition, the other interesting aspect from this FAD is the significantly smaller crack size that is tolerable in hydrogen service, with the maximum permissible crack reducing from 30 mm x 97 mm for non-hydrogen service to 12 mm x 3 3mm for hydrogen service. The impact of this decrease in crack tolerance is that inspection programs for hydrogen service will need to be more frequent and focussed on the identification of crack-like defects at an earlier stage than industry is currently used to.
Due to the importance of fatigue and fracture, other aspects, such as residual stresses and strain hardening, become important, as they act to decrease tolerance to both fatigue and fracture. Existing practices in pipeline construction will need to be modified to maximise the pipeline life in hydrogen service. This will likely include needing to refine welding practices, reduce cold-bend limits, reduce acceptable defect limits, improve bolted joint integrity practices and may include needing to utilise post-weld heat treatment.
However, it is not all doom and gloom. The practices required, including design, construction, and inspection, are currently known, and commonly practised in industry.
Integrating hydrogen into pipeline design and construction will be more a case of returning to our roots (neglecting some advances in pipeline design and fabrication, in particular high strength materials), employing fundamental assessments and modifying our design, construction, and inspection practices to achieve acceptable long-term integrity. The future is green, but pipeliners need to ensure care is taken at the design and construction stages to ensure hydrogen continues to be part of that green future.
Warren Brown, Ph.D., B. Eng, P.Eng., ASME Fellow is a member of various codes and standards committees and working groups for both ASME and AS1210. He is a Principal Engineer and founder of Integrity Engineering Solutions, where he works with a team of dedicated world-leading engineers, who enjoy the day-to-day challenges of solving the unsolvable.
For more information visit Integrity Engineering Solutions.
This article featured in the May edition of The Australian Pipeliner.