TWI Frequently asked questions
by David Abson
Wet underwater welding requires considerable skill and, depending on materials and consumables, carries a high risk of fabrication hydrogen cracking. For critical applications, it should only be undertaken by experienced welder divers using established procedures. Also, as there are wide differences in the operability and resulting weld quality obtained with different commercially-available electrodes, the choice of welding consumables should be made with care.
Whilst satisfactory welds can generally be made in the flat position, and, with the better electrodes, in the vertical position, welding overhead presents a considerable challenge, and weld quality in this position is likely to be poorer than in the other welding positions. In spite of this difficulty, it has been recognised for many years that welds of acceptable integrity can be deposited by this process.
Satisfactory repairs have been reported for U.S.A. Navy ships [1-3] and for offshore structures. [1,2] Successful repairs have also been carried out to offshore structures in the Gulf of Mexico, following hurricane damage, [4,5] and in the North Sea. [6] The integrity and mechanical properties of wet underwater welds have been evaluated by a number of authors e.g. [3,7] , and welds that meet AWS D3.6 [8] class A requirements (that are the same as for welds deposited in air) have been reported [9-11] . Ferritic weld deposits generally show only modest ductility and impact toughness, with Ni-base deposits giving better mechanical properties.
In nuclear applications, satisfactory repairs to stainless steels have been carried out underwater, using stainless steel manual metal arc electrodes. [12,13] However, it should be noted that the welding of ferritic steel with stainless steel electrodes is generally not successful, as fusion boundary cracking, and sometimes solidification cracking, occur. [1,14]
The semi-automatic wet underwater welding processes 'water curtain welding' (with the action of a conical water jet containing a gas shield) and flux-cored wire welding (without a gas shield) have been used with some success. The former is capable of producing high integrity welds. [15,16] Whilst success has been claimed for the latter in the repair of ships [17] and pipe-lines, [18,19] the quality of welds has generally not reached that achieved with the other welding processes.
References
- Weldasearch literature database to supplement what you find on this site.
