This project develops measurements, modeling, and science relevant to the effect of hydrogen on materials. Mechanical measurements focus on the fatigue and fracture properties of pipeline and pressure vessel steels. The project seeks to predict the behavior of candidate steels in a hydrogen environment with phenomenological and physics-based models. The model predictions allow code modifications that are used by industry. Modern scientific techniques are employed to understand the mechanisms that cause degradation of metals in hydrogen.
Hydrogen is known to have a deleterious effect on steels and other metals, but steels are the most cost-effective and commonly used materials for pipelines and pressure vessels. We are collaborating with the code bodies (ASME B31.12 and ISO 11114-4), DOT, and DOE, to enable the implementation of advanced pipeline and pressure vessel materials to reduce cost while maintaining safe operation.
NIST has a unique facility for measuring mechanical properties of structural materials in pressurized gases. Our primary focus is fatigue measurements in high-pressure hydrogen gas, but our capability is applicable to all high-pressure gas environments, particularly flammable gases.
Two load frames, each with a high-pressure test chamber, can be run simultaneously and at different hydrogen (or other gas) pressures. One chamber can test a single specimen in a gas atmosphere at up to 140 MPa, and the other can test up to 10 specimens simultaneously in gas pressurized up to 38 MPa. The measurements are remotely and automatically operated for safety, reliability and repeatability.
We have developed a model that uses the fatigue data and pipeline design inputs to predict the lifetime of a hydrogen pipeline. The model can predict fatigue crack growth rate as a function of operating pressure, load frequency, and load ratio and can demonstrate differences attributable to different microstructures. Estimates of lifetimes can be output as a function of existing flaw size. The phenomenological model is now being further developed into a physics-based model that will require more fundamental properties, such as microstructure and diffusivity, and will be fully predictive of the material behavior in a hydrogen gas environment, providing input for design of future alloys.
Neutron and synchrotron radiation measurements are used to measure the effect of hydrogen on the diffusivity, the strain of the lattice, changes in dislocation density, and phonon dispersion.
Our group has developed a test apparatus (for which we received a patent in 2015) and method that simultaneously measures 10 specimens at once, and maintains specific environmental and loading conditions until all 10 specimens have completed testing. Before we invented our test methodology, it took too long to determine a set of critical data large enough to be of use to the industry.
We have completed over 150 fatigue tests on base metals, welds, and the heat-affected zones of candidate steels.
We led a modification to the ASME B31.12. This modification permits the use of X70 steel rather than X52 steel, which would result in a savings of over $1 million per mile of pipeline.
We have generated 16 publications on the data and model from this Project.
Amaro RL, Rustagi, N., Findley, KO, Drexler, ES, Slifka, AJ (2014) Modeling the fatigue crack growth of X100 Pipeline Steels in Gaseous Hydrogen. International Journal of Fatigue, 59, 262-271.
Amaro RL, Drexler, E. S., Slifka, A. J. (2014), Fatigue Crack Growth Modeling of Pipeline Steels in High Pressure Gaseous Hydrogen. International Journal of Fatigue. 64, 249–257.
Drexler ES, Slifka, A. J., Amaro, R. L., Barbosa, N., Lauria, D. S., Hayden, L. E., Stalheim, D. G. (2014) Fatigue Crack Growth Rates of API X70 Pipeline Steel in a Pressurized Hydrogen Gas Environment. Fracture and Fatigue of Engineering Materials and Structures, 37, 517–525.
Drexler ES, McColskey, J. D., Dvorak, M., Rustagi, N., Lauria, D. S., and Slifka, A. J. (2014) Apparatus for simultaneous fatigue testing of multiple compact tension specimens in air and controlled (harsh) environments. Experimental Techniques, published online March 4, 2014.
Slifka AJ, Drexler ES, Nanninga NE, et al. (2014) Fatigue crack growth of two pipeline steels in a pressurized hydrogen environment. Corrosion Science. 78, 313-321.
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