Towards the establishment of weldability test standards for hydrogen-assisted cold cracking

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Our depth of understanding on these points has matured significantly over time and, while there is not always universal agreement, it is at least possible to start highlighting factors important to standards. This paper examines these factors, including the welding parameters, restraint, hydrogen, and cracking index. When comparing different alloys having different thermal characteristics, the use of constant welding parameters (common practice) will result in variable weld penetration and weld pool shape, which can influence grain shape and microstructural features, which can result in inequitable weldability comparisons. Welding on test coupons having different dimensions can affect restraint, which will influence the residual stresses around the weldment. High restraint usually results in higher crack susceptibility. Also, hydrogen content present in a weldment depends on the thermal history, welding parameters, and surrounding atmosphere humidity, with high hydrogen contents associated to great cracking susceptibility. Finally, the selection of an appropriate cracking index is required for data analysis. Quantifications of crack length and minimum preheat temperature are common indexes used for comparison. Critical stress and hydrogen content are other indexes. But how well these indexes actually represent weldability are contentious issues. This paper will examine and quantify these issues in detail, thus providing the reader with an appreciation of all things that must be considered when preparing a standardized procedure for weldability testing.

Micromechanical characterisation of weld metal susceptibility to hydrogen-assisted cold cracking using instrumented indentation

“…However, with the improvements in the steel-making process and a consequent reduction in steel hardenability, an increased tendency for HACC to occur in the weld metal (WM) rather than the HAZ is suggested [3,17,21,22]. The prevalence of weld metal hydrogen-assisted cold cracking (WMHACC) over heat-affected zone hydrogen cracking (HAZ HACC) has been suggested to be the consequence of changes in the alloy content and the as-cast microstructure of the parent plate.…”

“…The simplest proxy used to define microstructural susceptibility to hydrogen cracking is hardness [2][3][4]17]. It is therefore not surprising that hardness control criterions have been extensively codified [29][30][31].…”

“…Coupled with the high levels of restraint as a result of clamping and the lifting-lowering stresses, the pipeline is subjected to during construction, the root pass is generally accepted as the most vulnerable pass with respect to susceptibly to hydrogen-assisted cold cracking (HACC). Although the exact mechanism governing the initiation and propagation of hydrogen cracks is still in contention, it is generally accepted that hydrogen cracks occur when critical levels of hydrogen interact with a susceptible microstructure when a weld is subjected to a threshold level of stress [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Preheat can minimise the risk of cracking [2][3][4]; however, it limits weld productivity and adds costs.…”

“…Although the exact mechanism governing the initiation and propagation of hydrogen cracks is still in contention, it is generally accepted that hydrogen cracks occur when critical levels of hydrogen interact with a susceptible microstructure when a weld is subjected to a threshold level of stress [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Preheat can minimise the risk of cracking [2][3][4]; however, it limits weld productivity and adds costs. To ensure that the risk of HACC is designed out of the weld procedure, evaluation of the conditions for the onset of HACC needs to be established with confidence.…”

An experimental study of high-hydrogen welding processes

“…Excessive content of hydrogen in the steel welded joints causes decrease of metal plasticity and is a reason of formation of welding defects and imperfections, such as porosity and cold cracks (Pokhodnya et al, 2004;Kozak, 2011;Pańcikiewicz et al, 2013;Kurji and Coniglio, 2015). Therefore, problems connected with measurements of hydrogen content in joints have been a field of interest for many years (Padhy et al, 2015a, Kühn et al, 2013.…”