Literature Survey of Gaseous Hydrogen Effects on the Mechanical Properties of Carbon and Low Alloy Steels

Literature survey has been performed for a compendium of mechanical properties of carbon and low alloy steels following hydrogen exposure. The property sets include yield strength, ultimate tensile strength, uniform elongation, reduction of area, threshold stress intensity factor, fracture toughness, and fatigue crack growth. These properties are drawn from literature sources under a variety of test methods and conditions. However, the collection of literature data is by no means complete, but the diversity of data and dependency of results in test method is sufficient to warrant a design and implementation of a thorough test program. The program would be needed to enable a defensible demonstration of structural integrity of a pressurized hydrogen system. It is essential that the environmental variables be well-defined (e.g., the applicable hydrogen gas pressure range and the test strain rate) and the specimen preparation be realistically consistent (such as the techniques to charge hydrogen and to maintain the hydrogen concentration in the specimens). INTRODUCTION An infrastructure of new and existing pipelines and systems will be required to carry and to deliver hydrogen as an alternative energy source under the hydrogen economy. Carbon and low alloy steels of moderate strength are currently used in hydrogen delivery systems as well as in the existing natural gas systems. It is critical to understand the material response of these standard pipeline materials specified by the American Petroleum Institute (API) [1] when they are subject to pressurized gases of pure hydrogen or its mixture with methane since hydrogen is well known in deteriorating the mechanical properties of steels. A literature survey for existing mechanical property data on carbon and low alloy steels exposed to hydrogen gas was conducted to support this program for hydrogen pipeline life management. This paper documents the data available in the open literature. In the evaluation of the fitness-for-service for the line pipes used to transport hydrogen gas, the mechanical properties relevant to new construction or extended life of existing systems include the yield stress or yield strength (σy); ultimate tensile strength (UTS); elongation; reduction of area; fracture toughness expressed by the critical stress intensity factor KIC or KJC, J-integral (J), or crack growth resistance curve (J-R); the stress intensity factor threshold or the stress intensity factor at crack arrest (Kth) below which no crack growth in the hydrogen environment is likely; and the fatigue crack growth rate (da/dN, where a is the crack length and N is the number of cycles). The fatigue testing is typically in terms of the difference of the maximum and minimum stress intensity factors or ∆K= KmaxKmin, and the cyclic stress ratio, R= Kmin/Kmax. The change of mechanical properties is caused by the material response to hydrogen. However, the form of exposure or the type of attack directly affects the degradation mechanism in the materials, and results in various, sometimes