Knowledge Bank

Oil and gas companies have been experiencing catastrophic subsea pipeline fracturing and failure due to hydrogen assisted cracking (HAC). The cracking originates from dissimilar metal welds (DMW) on high strength steel forgings with Ni-base or austenitic stainless steel filler metals after hydrogen slowly diffuses into the dissimilar transition zone in hydrogen containing environments. The welding research group at the OSU materials science and engineering department is currently conducting Delayed Hydrogen Cracking tests (DHCT) on DMW samples to determine the conditions for failure utilizing constant loading conditions and simultaneous hydrogen charging. Additional hydrogen measurement capabilities were required to quantify the maximum amount of hydrogen, which diffuses into the sample before it fails in the DHCT test (hydrogen saturation time), and the rate at which hydrogen diffuses in and out of the sample (hydrogen diffusion coefficients). A gas chromatography thermal conductivity detector (GC TCD) was modified to test DHCT samples for diffusible hydrogen content. The GC TCD functions by flowing nitrogen gas over a hydrogen charged sample, collecting and measuring the diffused gas in the TCD. Software was developed in LabVIEW to collect and analyze these voltage and temperature signals. Utilizing a personally designed calibration valve, the GC TCD calculates the volume of hydrogen within an unknown sample by comparing the signals from known volumes of hydrogen generated by the valve. In order to characterize and compare the hydrogen measurements between DHCT samples, a data base is in development of the hydrogen content and diffusion rates within samples of varying compositions, dimensions, and charging periods. When complete, oil and gas companies can use the DHCT test to prevent future failures by evaluation the HAC susceptibility of undersea pipes that approach the observed maximum load, hydrogen content, and time required for a fracture to occur.