Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Multi-physics Model to Assess Hydrogen Assisted Cold Cracking
1Huan Wu, 1Shaun Smart, 1Tyler London, 1Valerio Carollo, 2Hongbiao Dong
Cambridge, United Kingdom
2School of Engineering, University of Leicester, Leicester, United Kingdom

1Advanced Manufacturing Technologies, TWI Ltd,

slowly diffusing through the solidified material and being driven byconcentration gradients and hydrostatic stress gradients, reaches alocation where the combination of susceptible microstructure, residualstress, and hydrogen concentration exceeds a critical threshold.
Therefore, if inspection is carried out too soon after welding, these cracks
may not be detected. On the other hand, excessive delays after welding
prior to inspection can have significant financial implications onproduction (Pargeter, 2003).

ABSTRACT
Hydrogen-assisted cold cracking (HACC) is one of the most common
forms of fabrication cracking in the welding of ferritic steels. HACCoccurs when hydrogen becomes trapped inside the fusion zone or heataffected zone during rapid cooling, and, in the presence of sufficiently
high welding residual stresses and a susceptible microstructure, causes
cracks or micro-fissures to occur. Cracking can occur several hours afterwelding, and most previous work to evaluate the risk of HACC or thenecessary delay before inspection for hydrogen cracks has been
empirical. In this paper, a multi-physics modelling approach to predictthe risk of HACC is presented. With calibration to physicalmeasurements, the model can minimise the number of welding trials
undertaken and provide an enhanced understanding of the mechanisms
and combinations of factors leading to HACC occurring.

A significant body of work has focused on developing pre-heatrequirements or allowable heat input limits for high strength steels to
mitigate the risk of HACC (see, for example, Arsic et al, 2015; Kurji andConiglio, 2015). These studies almost exclusively rely on empiricalmethods or welding trials to observe how different combinations of joint
design, levels of restraints, and welding parameters lead to cracking (orthe absence of cracking). Whilst these empirical studies provide physicalevidence for how to control or mitigate the risk of HACC, they provide
limited insight into the critical combinations that give rise to HACC.
That said, controls for the avoidance of HAZ hydrogen cracking
developed experimentally, when applied correctly, can be extremelyeffective. However, due to the development of high strength leancomposition steels, such as QT grades, hydrogen cracking in the weld
metal has become a dominant mechanism, even when HAZ cracking
avoidance is followed. Limited research has focused on this issue.

KEY WORDS: Hydrogen; cold cracking; multi-physics simulation;
finite element analysis; computational welding mechanics

INTRODUCTION
Current trends in mining, heavy construction equipment, wind towers
and bridge construction focus on lightweight, high strength steels,
typically with yield strengths between 690MPa and 1100MPa, to reduce
CO2 emissions and increase energy efficiency (Schaupp et al, 2020).
Despite their general weldability, high strength steels are susceptible tohydrogen-assisted cold cracking (HACC) due to their martensitic andbainitic microstructures.

To that end, this study focused on developing a multi-physics modelling
approach that can be used to identify the local criteria of stress,
microstructure, and hydrogen concentration that may give rise to HACC.
The aim was to have a more mechanistic understanding of thecombination of factors that give rise to HACC so that such a model could
potentially be used to optimize the delay after welding prior toinspection. Therefore, physical welding trials were undertaken to provide
baseline validation data that could be used to compare to predictions
from the model.

During welding, hydrogen enters the fusion zone through thesurrounding environment and through diffusible hydrogen in the filler
material. A local critical combination of hydrogen, mechanical stress,and microstructure can lead to fissures or cracking in the fusion zone orheat affected zone (HAZ). This need not occur immediately afterwelding; indeed, it is well-established that there can be some delay
between the completion of welding and the formation of hydrogencracks. This occurs because cracking does not arise until the hydrogen,In this paper, firstly, the experimental test setup is described; secondly,
the description of the multi-physics model is given; thirdly, a comparison
between the model and the measurements is made; and, finally, a3027