ABSTRACT A new underwater welding process has been under continuous development since 1968. It permits the welder/diver to work in-the-wet while the actual welding is performed in a dry gaseous environment using a specially-developed portable miniature habitat. The actual welding, done by a metal-inert-gas (MIG) process, consistently produces API 1104 Code welds in all welding positions in a large range of steel types and grades. Successful welds have been made to depths of 95 feet possible applications include new construction and repair of virtually any steel subsea structure with surface-quality welding. It is believed that the process will be adaptable to aluminum and any other weldable material. INTRODUCTION Early Welding Developments Welding underwater has been done with varying degrees of success from the beginning of the arc welding process. The achievement of quality underwater welds has always been hampered by the quenching effect of the water on the heat-affected zone and the deposited weld metal. Prior commercial attempts, as well as those used by the various navies of the world,1 have attempted to remove this unfavorable quenching effect by using a stick electrode with a special coating that generates a gas bubble around the arc as illustrated in Figure 1. Additional efforts to achieve quality welds have been made with the MIG process generating a large free bubble around the arc for the same purpose. All such attempts with both processes have, until recently, produced a marginal weld which rarely approached acceptable standards. This is attributed to such factors as the size of the bubble which, being too small, allowed a rapid quench. With increasing water depths, the size of the bubble is compressed further, with still more unfavorable results. In unfavorable welding positions, the free bubble becomes even more difficult to control. These and similar factors lead to welds with an uneven deposit of weld metal containing entrapped gas and/or slag material. The quenched metal in the heat-affected zone becomes too brittle resulting in an inferior weld. Recent Welding Developments Stick Electrode A recent process which was the subject of a previous paper2 has been commercially introduced in this country and used in some locations overseas. This process is thought to use a stick electrode with a special coating to give a larger, more controllable, free bubble. A similar process currently under development in England has been used on at least one commercial job. Although little has been published about the technical aspects of this process, it is believed to represent the best efforts with an optimum coating on the rod combined with rigorous and continuous training of the welder/diver to an acceptable weld under many conditions. It is known that special must be used with each different type of metal. Further, inferior results have been reported when welding high carbon, high strength steels.