Post Underwater Wet Welding Heat Treatment by Underwater Wet Induction Heating

Wet welding procedures of Class A structural ship steels frequently fail to comply with the American Welding Society (AWS) D3.6M, Underwater Welding Code, in the maximum hardness criterion for the heat-affected zone (HAZ). The maximum hardness accepted in a welded joint is 325 HV for higher-strength steel (yield strength > 350 MPa). In multi-pass welds, this problem occurs frequently and is restricted to the HAZ of the capping passes. The HAZ of the root and filling passes are softened by the reheating promoted by their respective subsequent passes. This paper presents the results of exploratory research into postweld underwater electromagnetic induction heating. The objective of the research was to evaluate the ability of induction heating to soften the specific high-hardness HAZs in underwater conditions. The results showed that this technique could reduce the maximum HAZ hardness of low-carbon structural ship steel welds to values below 325 HV, which is the maximum accepted by AWS for Class A welds. The induction-heated zone reached a maximum depth of about 10 mm, which is considered adequate to treat the HAZ of cap-ping passes in underwater wet welds.

Assessment of the Use of Negative Polarity in Double-Wire MIG/MAG-Welding Filling Passes

The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wire MIG/MAG-welding filling passes. A comparative study of the conventional technique (two wires working with pulsed DCEP) and the proposed combinations of pulsed DCEP in the lead wire with pulsed DCEN in the trail wire and pulsed DCEP in the lead wire with controlled short-circuit CSC(-) in the trail wire was carried out. The mean current in each wire and the ratio of travel speed to wire feed rate (for the same bead volume per unit weld length), as well as wire type and size, shielding gas composition and joint type (a butt joint in a flat position), were kept constant. Bead surface finish and geometry, deposition efficiency and maximum travel speed for each combination were evaluated. In conclusion, the use of negative polarity in the trail wire increased the deposition rate (higher travel speeds for the same bead) compared with the use of pulsed DCEP in both wires but at the cost of reduced operational robustness, as the conventional technique allowed a sound bead to be produced over a wider range of travel speeds. In addition, beads welded using negative polarity had smaller fusion zones and narrower heat-affected zones but higher convexities.