M. Hamasaki (Government Industrial Research Institute, Japan) and M. Watanabe (The Weld­ing Institute of Japan and Osaka University) have described the development in UWW in Japan. Among the methods being used are gravity welding and firecracker welding (also known in Europe as the Elin-Hafergut Method). In the latter process either one or two electrodes are set horizontally in weld joint and covered with grooved copper blocks before ignition. Good results were claimed for the firecracker method. Still more interesting, perhaps, is the water curtain type of CO2 (Mig) welding method which has been developed at the Government In­dustrial Research Institute. This method uses a dual nozzle which provides a shielding gas flow from an inner nozzle and a concentric flow of water from an outer nozzle. Both flux-cored and solid wire electrodes have been used, and the maximum speed achieved with each was 1.2 and 1.3 m/min respectively. Butt and fillet welds were made experimentally. Work has also been done elsewhere on the use of shielding gas introduced at a slightly greater pressure than that of the ambient water at depth.

Investigations have been conducted at the Japanese Institute of Metals with a tech­nique called “water plus gas shielding” for plasma-arc welding. Basically, the principle is the same as water-curtain Mig, but in this instance water flows from 12 holes in the bottom of the nozzle. Arc voltages could be as low as 20 V but increased with a greater depth of water. The process is claimed to give good results down to depths of 300 m. Its disadvantages are slow running speed, 60-80 mm/min, and the fact that it cannot be applied to rimming steel.

A. W. Stalker, 1974, dealt with tests carried out to assess the underwater running characteristics and crack susceptibility of various electrode types. The most promising were found to be a ferritic electrode with an oxidizing iron flux covering and a high nickel austenitic type. Even with these electrodes, however, it was necessary to apply continuous heating during the welding cycle to avoid hydrogen cracking in butt welds on carbon-manganese structural steels. In a second series of tests designed to give a preliminary assessment of arc behavior in a hyperbaric environment Tig, Mig and Manual metal-arc welds were made at pressures upto 32 bar.

Takemasu et al. in 1982 conducted laboratory tests on fire cracker welding simulating pressures down to 100 m. The beads deposited with commercial electrodes had both good appearance and sound mechanical properties.

Shinada K, et al., 1982 reported the use of remote controlled fully automated MAG welding process for underwater welding 12 mm thick pipes at 10 m water depth using 1.2 mm diameter solid electrode wire and 75% Ar 25% CO2 gas mixture in 3 passes. Power source was d. c. electrode positive. The quality of underwater welds was equivalent to that obtainable on land.

Stevenson A. W. in 1983 discussed the techniques for off-shore repairs and strengthening procedures including underwater welding, highlighting the ways in which an underwater contractor can help.

Allum C. J., 1982 discussed the role played by TIG welding in underwater applications. The process has been reported to give good results upto 500 m depth. The nature of TIG arc significantly changes with increasing depth (pressure around the arc). Above 30 bars arc appearance becomes highly distorted due to refractive index variations between the arc and the observer (distance of about 70 cm). Manual arc manipulation becomes difficult. It is a matter of speculation on whether TIG is suitable for mediterranean waters (2,500 m deep).

Allum C. J. 1983 discussed the scope of the process of dry hyperbaric underwater welding. Automated welding appears to be a possible solution in deep waters because of low stability and poor visibility and manoeverability limiting the use of manual process. It has also been pointed out that the arc could be stabilized by using magnetic field.

Delaune, P. T. Jr., in 1987 reported the use of AWS D 3.6 specifications for conveniently specifying and obtaining underwater welds of predictable performance level. These specifica­tions enable a designer to choose the weld type for a given situation and formulate a fracture control plan.