Hydrogen-induced cold cracking is a huge challenge in underwater wet welding. In the present study, the influence of water depth on the diffusible and residually stored hydrogen content is investigated for the case of underwater wet shielded metal arc welding. The welding is carried out in a simulated water depth of 5, 20, 40, and 60 m with four stick electrodes specifically developed for underwater wet welding. The influence of the welding current, the arc voltage and the electrode’s composition on the diffusible hydrogen content are considered. To obtain reproducible welding conditions, a fully automated multi-axis welding system is used inside a pressure chamber. The water depth is simulated by setting the internal pressure up to 6 bar, equivalent to 60 m water depth. A large amount of samples are analysed and statistical method are used to evaluate the results. The results show a significant reduction of the diffusible hydrogen and an increase of residual hydrogen in the joining zone with increasing water depth.

Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by −34% in 30 m simulated water depth.

Due to the rising number of offshore structures all over the world, underwater wet welding has become increasingly relevant, mainly as a repair method. Welding in direct contact with water involves numerous challenges. A topic focused by many studies is the risk of hydrogen‐induced cracking in wet weldments due to hardness values of up to 500 HV 0.2 in the heat‐affected zone (HAZ) and high levels of diffusible hydrogen in the weld metal. The risk of cracking increases as the equivalent carbon content rises, because the potential to form martensitic structures within the HAZ rises too. Thus, high‐strength steels are especially prone to hydrogen‐induced cracking and are considered unsafe for underwater wet repair weldments.

The European standard ISO 3690 regulates the measurement of diffusible hydrogen in arc-welded metal. It was designed for different welding methods performed in dry atmosphere (20% humidity). Some details of the standard are not applicable for wet underwater welding. The objective of this study was to extend the applicability of DIN EN ISO 3690:2018-12 to underwater wet-shielded metal arc welding (SMAW). Four different aspects regulated within the standard were accounted for: (1) sample dimensions and number of samples taken simultaneously; (2) time limitations defined by the standard regarding the welding and the cleaning process; (3) time, temperature, and method defined for analysis of the diffusible hydrogen content; (4) normalization of the hydrogen concentration measured. Underwater wet welding was performed using an automated, arc voltage-controlled welding machine. The results are discussed in light of standard DIN EN ISO 3690, and recommendations are provided for the analysis of diffusible hydrogen content upon underwater wet welding.

Plasma welding is characterized by a high concentration of energy, which allows for high welding speed and leads to less distortion and residual stresses compared to conventional welding processes. Due to the local and controlled heat input, the process is suitable for sheet metal from ≈ 0.1 mm (micro plasma) up to ≈ 10 mm. In the case of aluminum and its alloys, the natural aluminum oxide layer on the metal surface limits the productivity of the plasma welding process. The electrically isolating and thermally insulating Al ₂ O ₃ layer has a significantly higher melting point compared to the aluminum ( T _m(Al2O3) = 2072 °C vs. T _m(Al) = 660 °C). The oxide layer hinders the formation of a stable arc and can even impede the joining formation. In order to remove the oxide layer and to produce quality welds with a DC process, it is necessary to weld with reverse polarity to use the principle of cathodic surface cleaning. However, this leads to increased electrode wear and increased penetration depth, which is not always desirable. In the study presented, the use of silane to reduce the oxygen content in the welding atmosphere as well as to remove the natural aluminum oxide layer on the metal surface was investigated. As previous studies have shown that the use of silane-doped plasma-gases is suitable for removing the superficial oxide layer on aluminum components, high-quality welded joints were expected. Quality welds with sufficient dilution were achieved using a transferred arc silane-doped helium plasma. In contrast, welding with an argon-silane mixture led to excessive pores formation. Additionally challenges to stabilize the arc process were identified and ramifications with respect to process optimization are discussed.

As a lightweight construction material, aluminum plays a key role in weight reduction and, thus, sustainability in the transport industry. The brazing of aluminum and its alloys is impeded by the natural passivating oxide layer, which interferes with the brazing process. The presented study investigates the possibility of using a thermal silane-doped argon plasma to reduce this oxide layer in situ and thus eliminating the need to use hazardous chemical fluxes to enable high-quality brazing. Using plasma spectroscopy and an oxygen partial pressure probe, it was shown that a silane-doped argon plasma could significantly reduce the oxygen concentration around the plasma in a thermal plasma brazing process. Oxygen concentrations below 10⁻¹⁶ vol.-% were achieved. Additionally, metallographic analyses showed that the thickness of an artificially produced Al₂O₃-Layer on top of AlMg1 samples could be substantially reduced by more than 50%. With the oxide layer removed and inhibition of re-oxidation, silane-doped plasma brazing has the potential to become an economically efficient new joining method.