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

Abstract

Hydrogen-assisted cold cracking is generally accepted to be the consequence of a critical concentration of hydrogen trapped within a susceptible microstructure and subjected to a threshold level of stress. Traditionally, hardness has been used as a proxy for establishing the critical limits above which the risk of a hydrogen crack propagating is considered significant. However, developments in the steel-making process, in particular thermomechanically controlled processing, has brought into question the suitability of empirical hardness limits developed using older generation steels. In this paper, a safe welding boundary was established for single-pass root runs for API 5 L X70 steel welded with E6010 electrodes. Across this boundary, it was shown that hydrogen cracks were present in welds with hardness's well below the traditionally accepted threshold of 350 HV. This paper explores the use of nanoindentation as means of quantifying the susceptibility of welds deposited on high-strength low-alloy steels, using shielded metal arc welding, to hydrogen-assisted cold cracking. It is suggested that the use of the hardness/elastic modulus (H/E) ratio, which is directly related to the yield strength of a material, is a more suitable parameter to predict weld metal hydrogen-assisted cold cracking (HACC) susceptibility than is the hardness alone.

Quenched and Tempered Steels Welded Structures: Modified Gas Metal Arc Welding-Pulse vs. Shielded Metal Arc Welding

“…To examine the susceptibly of the weld metal and HAZ to HACC, transverse sections of the welds deposited on the MWIC weldability test were examined under ×400 optimal magnification [38] and presented in Figure 9. The examination did not yield any evidence of hydrogen cracking, suggesting that under high levels of restraint, as simulated by the MWIC test, both processes were equally resistant to hydrogen cracking under the employed welding procedure.…”

“…The examination did not yield any evidence of hydrogen cracking, suggesting that under high levels of restraint, as simulated by the MWIC test, both processes were equally resistant to hydrogen cracking under the employed welding procedure. To examine the susceptibly of the weld metal and HAZ to HACC, transverse sections of the welds deposited on the MWIC weldability test were examined under ×400 optimal magnification [38] and presented in Figure 9. The examination did not yield any evidence of hydrogen cracking, suggesting that under high levels of restraint, as simulated by the MWIC test, both processes were equally resistant to hydrogen cracking under the employed welding procedure.…”

Modified WIC test: an efficient and effective tool for evaluating pipeline girth weldability

“…The proposed geometric configuration of the MWIC Test was introduced after a series of iterative simulation and experimental studies aimed at improving the quality and consistency of the deposited weld bead [35]. The MWIC test has been designed (Figure 2) from the original geometric features of the WIC test.…”

“…Simulation cases were run for single pass welds deposited at a heat input of 0.65 kJ mm −1 on both 10 and 20 mm thick parent plate. The heat input for the simulation case was selected as it is suggested to be representative of field conditions [40] and can be experimentally replicated for validation on both the WIC and MWIC tests. To compare the two specimens temperature probes are used to ascertain the peak temperature and cooling rates at 6, 9 and 12 mm away from the weld centreline.…”

Temper Bead Welding of S420G2+M Steel in Water Environment

“…Weldability of such steel in the air environment is assessed as good. In the case of underwater welding it is necessary to keep rigorous technological regime, which is primarily aimed at reducing the tendency to form cold cracks in the welds [21,28]. Due to the growing need to conduct repair works of hydrotechnical facilities and subsea pipelines it is necessary to carry out research on weldability of high strength steels in the water environment [21,29].…”