A comprehensive testing program to determine the fatigue crack growth rate of pipeline steels in pressurized hydrogen gas was completed; the project was sponsored by the Department of Transportation, and was conducted in close collaboration with the ASME B31.12 Committee on Hydrogen Piping and Pipelines. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and a few tests at 0.01 Hz. Of particular interest to ASME and the Department of Transportation (DOT) was whether the X70 materials would exhibit higher fatigue crack growth rates than the X52 materials. These American Petroleum Institute (API) steels are designated based on yield strength, and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength. The X70 materials performed on par with the X52 materials in fatigue. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. This paper describes, in detail, the testing that formed the basis for the code modification.
Citation: Journal of Pressure Vessel Technology-Transactions of the ASME
Pub Type: Journals
fatigue, fatigue crack growth, hydrogen diffusion, hydrogen embrittlement, pipeline steel