Hydrogen embrittlement in vintage grade 290 pipeline steel and its welded region via ex-situ and in-situ testing
Rashiga Walallawita, Matthew C. Hinchliff, D. Sediako, John P. Quinn, Vincent Chou, Kim Walker
Abstract
The effect of hydrogen embrittlement on the base metal and seam welds of CSA Z245.1 Grade 290 pipeline steel was examined through slow strain rate tensile tests utilizing both gaseous ex-situ and in-situ testing methods, followed by fractographic analysis. Ex-situ testing was conducted after one month and two months of pre-charging in 100% hydrogen (99.999%) at room temperature under 2.07 MPa (300 psi) of pressure. In-situ testing was conducted in a custom autoclave setup which maintained 2.07 MPa of pressure throughout the test at room temperature. The tensile results from this study emphasize the significance of in-situ testing, revealing that the hydrogen embrittlement index for the base metal and weld samples tested in-situ were 30.5% and 19.8% higher compared to the next closest tested conditions. Specimens tested with in-situ hydrogen exposure displayed shallow dimples, cleavage, quasi-cleavage facets, and lamellar cleavage, in contrast to the clearer micro-void coalescence seen in ambient and ex-situ tests. In-situ tested specimens showed more prominent localized plasticity and micro-cracks compared to those tested under ambient, one-month, and two-month pre-charged ex-situ conditions. • In-situ hydrogen tests show higher embrittlement than ex-situ in vintage steel. • Fracture shifts from microvoid coalescence (ex-situ) to quasi-cleavage (in-situ). • HELP and HEDE mechanisms mainly drive hydrogen-assisted failure processes. • Gaseous ex-situ tests may misrepresent real-world hydrogen embrittlement.