- While pipelines are the safest, most economical way to transport fuels, the parameters used for codes and standards for the transport of hydrogen are based on tensile test data that is over 30 years old. In order to enable the design of safe pipelines and the use of hydrogen as an alternative fuel, a working understanding of the relationship between fatigue performance of pipeline steels and hydrogen gas pressure and loading parameters is needed.
- Since pipelines operate at low loading frequencies, fatigue data takes a very long time to produce. NIST has developed a measurement system that reduces this time by a factor of 10.
- Critical data from this project directly informs codes from ASME and CSA America.
- Based on 2011-2012 cost numbers from industry, use of X70 steel rather than X52 steel would result in a savings of over $1 million per mile of pipeline.
NIST has a unique capability 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. We use two load frames, each outfitted with a high-pressure chamber for mechanical measurements. 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 up to 38 MPa gas. The measurements are remotely and automatically operated for safety, reliability and repeatability.
We test modern pipeline steels such as X52, which have low carbon for weldability and predominantly acicular ferrite microstructures. Because higher-strength alloys such as X70 would permit future pipeline designs to be even more economical, we are testing those as well. An efficient way to transport hydrogen could be achieved by re-purposing existing pipelines, so we are also measuring the fatigue properties of older alloys. Older alloys have different microstructures and different chemistries, and therefore may behave differently in hydrogen. While our focus has been on base materials, we will soon begin a systematic matrix of tests on seam and girth welds, including the weld itself and the heat-affected zone, from both old and new pipelines.
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 and load frequency, and can account for different microstructures. Estimates of lifetimes can be output as a function of existing flaw size.
Industry members of the ASME B31.12 Committee on Hydrogen Piping and Pipelines have given us guidance on which materials to test and continue to guide us on the priorities for the modeling effort. The data from this project are being used by the committee to modify the code; prior to this work there was no information on fatigue crack growth of pipeline steels in hydrogen gas.
X52 tensile testing in both hydrogen and air. The two images on the right show the fracture surface of a specimen tested in air on top, and in hydrogen on bottom.