Fyfe engineers have developed an innovative model for hydrogen pipeline integrity in response to rapidly growing interest and activity in the hydrogen sector.
The Australian government has been working towards amending the National Gas Law and Regulations to bring renewable energy solutions including hydrogen and blended gasses into the long-standing national framework. However, policy has yet to catch up with industry activity.
Efficient storage and transportation are crucial for hydrogen’s economic viability. Using existing steel pipeline infrastructure can offer a dual solution; meeting both storage and transportation requirements and presenting a cost-effective option.
However, uncertainties arise when using these steel pipelines for hydrogen transmission, as hydrogen absorption can adversely affect the ductility, toughness, and fatigue life of steel pipelines.
Fyfe engineers have addressed these challenges by developing a mathematical model to predict fatigue life in new and existing hydrogen infrastructure. This innovative model considers factors such as the pipeline’s material properties, stress concentrations, operating conditions, a theoretical crack, and potential hydrogen embrittlement effects to accurately predict fatigue life in a cost-effective manner. This development by Fyfe engineers is a significant step towards ensuring the safe and efficient deployment and management of hydrogen pipelines.
Fatigue life explained
Fatigue life refers to the durability and longevity of a pipeline under cyclic loading conditions. It is a measure of how well the pipeline can withstand repeated stress cycles over time, without experiencing structural failure.
Fatigue occurs due to repeated pressure fluctuations, and other cyclic loading effects pipelines are subjected to during operation.
Hydrogen can interact with steel pipeline material, leading to hydrogen-induced cracking through the phenomena of hydrogen embrittlement. This interaction can reduce the pipeline’s ability to withstand cyclic loading, significantly impacting its fatigue life. Hydrogen atoms also diffuse into steel, causing internal pressure at material inclusions and promoting crack initiation and propagation.
To ensure an acceptable fatigue life for hydrogen pipelines, careful material selection, design considerations, and engineering practices are necessary. Engineers must consider factors such as the pipeline’s material properties, stress concentrations, operating conditions, and potential hydrogen embrittlement effects.
Fyfe’s approach to hydrogen pipeline integrity
To address and manage these considerations, Fyfe engineers working on complex hydrogen projects must conduct comprehensive engineering assessments and design solutions that are not only compliant with Australian standard AS 2885, but also look further afield for guidance from other internationally recognised standards.
This includes the American Society of Mechanical Engineers (ASME) B31.12 Standard on Hydrogen Piping and Pipelines. The world’s leading industry standard for hydrogen infrastructure design, B31.12 considers the unique properties and characteristics of hydrogen and hydrogen-blend gasses.
An innovative model to predict fatigue life
Over a period of six months spent researching crack data, integrating existing crack fitness-for-purpose standards, and drilling down into the minutiae of B31.12 option B (the performance-based method), Fyfe engineers developed a fatigue crack growth rate (FCGR) mathematical model. This model allows us to predict fatigue life in new and existing hydrogen pipelines. After developing the model, our engineers carried out multiple internal quality checks including achieving comparative results when checking against current research papers.
We have now used the FCGR model on feasibility projects for two separate clients, both involving new hydrogen pipeline infrastructure. The application of Fyfe’s FCGR model has resulted in significant material savings because it takes a sophisticated approach to fatigue life, rather than using ASME B31.12 option A (the prescriptive design method). This conservative approach is based on brittle fracture control and ductile fracture arrest and results in excessive pipeline thickness.
Fyfe engineers also evaluated a steel mill that produces hydrogen-ready API 5L pipeline steel, which complies with the ASME B31.12 threshold for stress-intensity factors of 55 MPa m^1/2.
See below for the FCGR and the S/N (stress/cycles) curves, an output from the FCGR model that allows our engineers to predict a design life based on an assumed detectable initial crack size. The FCGR model can then predict the remaining life of existing or new hydrogen pipelines. For existing hydrogen pipelines, the FCGR model can also be used to define the required inspection intervals in conjunction with the data gathered from intelligent pigs (devices used in pipeline inspection that provide data for engineers to analyse).
To learn more about how our model can add value on your hydrogen infrastructure project, please contact us.
