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.