TWI Industrial Member Report Summary 969/2010
By S Raghunathan
Underwater welding and cutting can be carried out using either dry (hyperbaric) or wet welding techniques. As a special habitat is not required, wet welding offers the advantages of low equipment costs and flexibility. Therefore, in situations where tight tolerances on mechanical properties are not essential, wet underwater welding is often the preferred repair technique.
Wet welding is typically carried out using the manual metal arc (MMA) process using electrodes that have a waterproof coating. The main limitations of MMA wet welding are the low production rate and the need for a specially trained diver.
The semi-automatic wet underwater flux-cored arc welding (FCAW) technique has been used quite widely in the former Soviet Union. Applications have included the repair of ships, pipelines and offshore structures. However, there is relatively little experience in Western Europe and the US of the FCAW process, particularly with respect to potential productivity benefits due to mechanisation. The E O Paton Electric Welding Institute (PWI) has developed wet welding techniques based on self-shielded FCAW process. Self-shielded FCAW wires have been developed specifically for operating in direct contact with water.
In a previous research project (Woloszyn, 2000); several different self-shielded consumables and types of FCAW equipment were assessed along with the operating characteristics of the flux-cored system. Woloszyn reported that though there are documented examples of applications of FCAW for underwater wet welding, no literature was found to precisely identify the level of quality attainable. He concluded that mechanised FCAW when applied to underwater wet welding shows promise, but recommended further development of welding procedures and consumables to bring the weld quality to an acceptable standard.
The primary purpose of this work was to further investigate the PWI self-shielded FCAW wire and study the benefits of a local habitat with self-shielded FCAW to increase shielding efficiency. Comparative trials were carried out with and without a local habitat using a wire brush shroud. Further multi-pass welding procedures for butt and fillet welds were qualified with the PWI PPS-AN1 wire.
- Carry out literature review of mechanised wet welding using FCAW.
- Study effects of a local habitat on the performance of wet welding using FCAW.
- Develop and qualify mechanised wet welding procedures.