Rotary friction welding (in particular stud welding) is easy to use underwater.
However, friction welding underwater can cause rapid cooling of the weld and may lead to poor weld properties - but there is a solution to the problem.
It has been established that when friction welding steel studs to steel plates, the quenching effect can give rise to excessive hardness and severe cracking - even at relatively shallow depths. The cooling efficiency of the water should be independent of depth, but there are minor changes due to temperature and salinity.
Fortunately, foamed plastics can be used to form a shroud around the weld region to protect it from the surrounding water and therefore eliminate the problem.
In its work on underwater friction welding of pipes, TWI found that use of a shroud on the outside of the pipe and a plug on the inside minimised hardness changes and gave acceptable welds.
FAQ: Can friction welding be carried out in hostile environments?