The paper describes principles of underwater welding and recent trends in research works undertaken for enhance welding technology and properties of underwater welds. Department of Materials Technology and Welding at Gdansk University of Technology (GUT) has been involved in underwater welding research for over 25 years. Investigations include technology of underwater welding, and weld properties examinations. All tests have been performed with the use of self designed stands allow to perform welds in shallow depths as well as the depths up to 1000 m. The main investigation directions performed at the Department of Materials Technology and Welding are presented:Weldability of HSLA steel and factors influencing susceptibility to cold cracking of welded joints. The effects of wet welding conditions on diffusible hydrogen amount in the welds. The effects of heat input, underwater welding depths and composition of shielded gases on welds toughness.

Wet welding is the most common method of welding in water environment. It is most often used for repairing of underwater parts of offshore structures. However, the water as a welding environment causes an increase of susceptibility of steels to cold cracking. For underwater constructions high strength low alloy (HSLA) steel are widely used. In wet welding condition a HSLA steel is characterized by high susceptibility to cold cracking. Temper Bead Welding (TBW) was chosen as a method to improve the weldability of S460N steel. The studies showed that TBW technique causes significant decrease of maximum hardness of heat affected zone (HAZ). The largest decrease in hardness occurred in specimens with the pitches in range 66-100%.

Among wet welding methods, the manual metal arc welding is most often used, hence majority of steel weldability test results accessible in the subject-matter literature concern the above mentioned process [4][5][6][11][12][13][14][15][16][17][18][19][20].Transferring the welding process to water environment results first of all in increasing diffusible hydrogen content in deposited metal, as well as in increased cooling rate. Manual metal arc welding in wet conditions generates the diffusible hydrogen content in deposited metal, of the order of a few dozen ml/100g Fe, depending on a type of shielding and welding conditions [14,15]. The tests [15,16] performed with the use of rutile-shielded electrodes, the most often applied in such conditions, showed that hydrogen content in deposited metal did not depend on a wetting degree of the shielding, but heat input was the decisive factor (Fig. 1).POLISH MARITIME RESEARCH 2(78)

Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check the influence of temper bead welding (TBW) on the weldability of the investigated steel. Non-destructive and destructive tests showed that S460ML steel has a high susceptibility to cold cracking. In all joints, hardness in the heat-affected zone (HAZ) was extended to the 400 HV10 values. Microscopic testing showed the presence of microcracks in the HAZ of all welded joints. TBW was chosen as the method to improve the weldability of the investigated steel. This technique allows for the reduction of the maximum hardness in the HAZ below the critical value of 380 HV10, as stated by the EN-ISO 15614-1:2017. It was determined that for S460ML steel, from the point of view of weldability, the pitch between two beads should be in the range 75%–100%. Also, if the pitch between two beads increases, the hardness, grain size, and number of cracks decreases. In all specimens where the hardness of the HAZ was below 380 HV10, there were no microcracks.

This paper shows results of weldability testing of fine-grained high-strength low-alloy S460N steel welded in water environment by covered electrodes. The tests were carried out by using the CTS test specimens with fillet welds. Four specimens were welded under water and one specimen in air. Welded joints were subjected to non-destructive visual and penetration tests. The accepted joints were then subjected to macroscopic and microscopic inspection and Vickers hardness measurements as well. The experiments showed that S460N steel welded in water environment is characterized by a high susceptibility to cold cracking.

Water as the welding environment determines some essential problems influencing steel weldability. Underwater welding of high strength steel joints causes increase susceptibility to cold cracking, which is an effect of much faster heat transfer from the weld area and presence of diffusible hydrogen causing increased metal fragility. The paper evaluates the susceptibility to cold cracking of the high strength S355G10+N steel used, among others, for ocean engineering and hydrotechnical structures, which require underwater welding. It has been found from the CTS test results that the investigated steel is susceptible to cold cracking in the wet welding process.

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Duplex stainless steels are very attractive constructional materials for use in aggressive environments because of their several advantages over austenitic stainless steels. Duplex steels have excellent pitting and crevice corrosion resistance, are highly resistant to chloride stress-corrosion cracking and are about twice as strong as common austenitic steels. Better properties are associated with their microstructures consisting of ferrite and austenite grains. However, with certain thermal treatments, these excellent properties may be reduced due to undesired changes in the steel microstructure, related mainly to different solid-state-precipitation processes. The impact toughness of the commercial 2205 duplex stainless steel and the higher-alloy super-duplex 2507 steel was investigated. Both steels were submitted to the ageing treatment in a temperature range between 500°C and 900°C with the exposure times of 6 min, 1 h and 10 h; in addition, light microscope examinations, hardness measurements and impact-toughness tests were performed. The main objective of the investigations was to determine the effect of the change in the microstructure on the mechanical properties of the steel.