ABSTRACT The problems in underwater wet welding of higher strength steels are identified. Engineering fundamentals are being considered to guide future research to overcome some of the limitations to deep wet underwater welding of higher strength steels. Six different approaches are suggested for research to increase the water depth for underwater welding. INTRODUCTION The demand for underwater wet welding repairs has always been strong because it provides a quick and economic means of reinstating marine structure close to design configurations. The quality of the underwater wet welds has been a concern but an Underwater Welding Specification (AWS D3.6) has provided the guidance for assuring that wet welds of sound quality are produced consistently. However it has been shown that the underwater welding technique is limited to steel of low carbon equivalent (Ceq < 0.40 wt. pct.) (1) and to depths of less than 325 feet. Unfortunately most of the platforms that are used in the North Sea are made with thick wall steels that have carbon equivalents greater than 0.40 wt. pct. It has been shown that wet welding of high carbon equivalent steel with ferritic electrodes results in cracking of the heat affected zone (HAZ). In the Gulf of Mexico wet welding techniques have been very successful because the thinner wall, low carbon equivalent steels are relatively easy to repair by wet welding. However even in this area some of the mudslide platforms at the mouth of the Mississippi river have the thicker, high carbon equivalent steels, and these may result in future repair problems. Deeper platforms are also being made to depths greater than the traditional 325 foot limit for wet welds. The quality of the ferritic wet welds deteriorates past the 325 foot depth and weldments cannot pass the requirements stipulated in AWS D3.6 Underwater Welding Specification (2). One of the solutions to the problem of welding higher strength steel has been the use of austenitic stainless steels or nickel base electrodes. These austenitic welds are able to retain hydrogen in solid solution and decrease the tendency for hydrogen cracking in the heat affected zones. However, experience has shown that welding with austenitic stainless steels results in restraint cracking because of the difference in thermal expansion between the ferritic base metal and the austenitic stainless steel weld metal. Although austenitic stainless steel wet welds are successful in reducing the susceptibility to hydrogen cracking in the HAZ, the presence of the restraint cracks in the weld metal adjacent to the HAZ prevents their use in this application. The nickel base electrodes are also successful in decreasing hydrogen cracking in the HAZ and since there is less difference in thermal expansion between the nickel weld metal and the ferritic base metal the weld metal deposit is virtually immune to the restraint cracking noted in the austenitic stainless steel welds. The thermal expansion compatibility between the weld deposit and the base metal can be evaluated from Figure 1 (3).