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

Nominal Stress Fatigue Assessment on Underwater Wet SMAW Fillet Welded Non-load-carrying
Attachments of Construction Steel
Oliver Brätz a, Thomas Wolf b, Julia Osten a, Thomas Hassel b, Knuth-Michael Henkel a,ca Fraunhofer Institute for Large Structures in Production Engineering IGPb

Rostock, Mecklenburg-Western Pomerania, Germany
Leibniz University Hannover, Institute of Materials Science (IW), Underwater Technology Centre Hannover (UWTH)
Garbsen, Lower Saxony, Germanyc University of Rostock, Chair of Joining TechnologyRostock, Mecklenburg-Western Pomerania, Germany

ABSTRACTQUALITY OF WET WELDS

In this paper, the aim was to determine the fatigue strength of underwater
performed repair welds because lower weld quality can be expected. Wetwelding partially causes internal defects and the high cooling rates resultin quenched microstructures. This is assumed to significantly reduce thefatigue behavior, so that the prevailing fatigue classification may not bevalid. Using different steel grades, non-load-carrying attachments werewet SMAW welded at different water depths. The samples were fatigue
tested and statistically evaluated. The fatigue strengths were found to bevery comparable to the atmospheric weld detail’s fatigue classes FAT71.

Wet welding causes specific conditions in arc welding that affect theprocess behavior itself and the resulting weld formation. The local
vaporization and as well as the dissociation of water in the arc
atmosphere leads to an impairment of the process stability. Furthermore,
there is a hyperbaric effect as a function of the water depth which affects
the arc formation. With respect to the metallurgy, further complex effects
of wet welding must be considered, cf. (Omajene et al., 2014).
The water as surrounding medium significantly increase the heatdissipation by convection which result in very high cooling rates afterwelding. On the one hand, there is a quenching effect in the weld metaland heat-affected zone (HAZ) resulting in strongly hardened microstructures for typical constructional steels for instance. In addition,
dissociated hydrogen which was first easily absorbed by weld pool
during welding cannot diffuse quick enough upon solidification and will
result in a strongly supersaturated weld metal. Partially, this hydrogen ispresent as diffusible hydrogen and provoke a hydrogen embrittlement of
the material. In case of a critical presence of a sufficient concentration ofdiffusible hydrogen, a critical local stress state and a susceptible material
or a material in a critical state there is a risk of hydrogen-assisted
cracking (HAC). This is a fundamental difficulty in wet weldingof steels, especially for grades with higher strength. In short, manual
wet welding requires extremely high skilled executing personnel.
Nonetheless, a reduction of the internal weld quality due toimperfections, e.g. pores, inclusions, and (micro-) cracks, will comefrom the special boundary conditions the greater the water depth isanyhow, cf. (Pessoa and Liu, 2021). Exemplary multi-pass butt joints for
weld metal investigation that were prepared by wet SMAW in different
water depths are presented comparatively in Fig. 1.
The achieved weld quality, with the typical imperfections, then again
affects the static strength behavior as well as the fatigue performances of
the joints and must be considered in case of underwater repairs on cyclic
loaded hydraulic structures (Almar-Næss, 1999). Mostly, fatigue
behavior is studied for specific application in the case of necessary
repairs, cf. (Pohl et al., 1996) (Rodríguez-Sánchez et al., 2011).

KEY WORDS: wet shielded metal arc welding; underwater wetwelding; underwater repair; fatigue strength; Wöhler test; S-N curve

INTRODUCTION
In the event of the necessity of damage repair or modify of hydraulicstructures effective methods are required allowing a simple and quickexecution. For the submerged parts specific aggravated environmental
conditions must be considered particularly. The wet shielded manual arc
welding (SMAW) is still widely applied due to its high flexibility andrelatively easy application possibility, if reasonable for the case.
Nevertheless, in consideration of the difficulties in wet welding itself as
well as the special metallurgy conditions usually a lower weld quality isachieved. When joining any non-loaded or quasi-non-loaded attachments
on cyclically loaded structures the fatigue strength of this structure will
be adversely affected. These weld details are categorized according todifferent standards but only on the condition that the welds are performed
under atmospheric dry conditions and in compliance with specified
quality criteria. Thus, in the absence of the exact knowledge about
fatigue strength of wet welded joints a valid assessment of structureservice life is not possible. Every wet welded constructional detail mustbe evaluated individually with respect to fatigue strength based on theactual characteristics, e.g. microstructure and weld quality.

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