Underwater Cutting Oxygen Purity
The oxygen purity for all underwater oxygen cutting should be 99.5 percentor greater. As the oxygen purity is reduced, so is the cutting efficiency. A one percent decrease in oxygen purity will result with a 25 percent reduction in cutting speed. In addition, the quality of the cut decreases and the amount of slag adherence increases. At oxygen purities of 95 percent or less, the operation becomes one of melting and washing out rather than cutting. Commercially available oxygen specifically for underwater cutting should be 99.9 percent pure.
Underwater cutting : Grounding the Work
Before conducting any type of electric arc cutting or welding, a ground cable must be attached to the work piece. The diver can either leave the surface with the cutting torch, ground cable and cutting electrodes or they can be lowered after arrival at the worksite. The first task is to clean a spot for the ground clamp. The spot should be in a position in frontof the diver and should be scraped or wire brushed shiny clean. For diver safety, only C-typeclamps should be used as grounding clamps for underwater cutting or welding operations. The clamp must be firmly secured to the work piece and the cable should have sufficient slack to prevent it from being pulled loose. The diver may elect to lightly tack weld the clamp in place whenthere is a possibility of it working loose. From time to time as the cut progresses, the diver may have to reposition the ground clamp to avoid becoming part of the electrical circuit.
Clean metal cuts better than corroded or growth-encrusted metal. Steel covered with ordinary mill scale and one or two thin coats of paint may be cut easily. Thick scale, thickpaint, barnacles and similar marine growth make cutting difficult and should be removed. An ordinary paint scrapperis useful in removing light scale and paint; however, for heavier growths, a high-pressure water jet cleaning tool may perform the cleaning process satisfactorily. If possible, it is important to clean both sides of the metal before cutting. Obstructions on the opposite side of the metal will clog the cut and prevent the cutting jet from blowing through. If inaccessible, striking the area to be cut with a heavy sledge hammer may sufficiently loosen scale on the opposite side