type E6Q13 for all positions except where the section size is too thin for 

 this size electrode. Other electrodes, such as waterproofed iron powder 

 electrodes, may he satisfactory. Qualification testing should he performed. 

 Electrodes for underwater welding are designed for straight polarity, i.e., 

 the electrode is negative. If reverse polarity is used underwater, the 

 electrode holder is consumed due to electrolitic action. It is important 

 that the electrode holder he insulated and be designed to permit easy 

 changing of electrodes by the diver. 



Power sources for underwater arc welding should be capable of delivering 

 at least 300 amperes of rectified or direct current. Because welding is 

 usually done at considerable distances from the power source, the welding 

 cables should be at least size 2/0. To facilitate maneuverability, the last 

 3 meters (1Q feet), of cable at the electrode holder is usually size 1/0. A 

 safety switch is installed in the circuit that is closed only while the 

 welder is actually welding. For good electrical continuity, the ground cable 

 must be securely attached to the work after first cleaning the contact area. 

 Provided the pieces to be welded fit together properly, 4.75-millimeter 

 fillet welds can develop 44 kilonewtons (10 000 pounds) tensile strength per 

 25.4 millimeters (1 inch). Using 4.75-millimeter electrodes and the drag 

 technique where the electrode is allowed to consume itself as it is pressed 

 against the work, 4.75-millimeter fillet welds are produced in a single 

 pass. Stringer bead technique should be used if additional weld reinforce- 

 ment is required. Because visibility is poor under water, multipass welds 

 are difficult to finish after the first bead is laid because the guiding 

 groove is filled. Fillet welds can be made in the horizontal, vertical, and 

 overhead positions. 



Bubbles generated during welding interfere with visibility. Welders 

 minimize this problem by welding toward themselves when making horizontal 

 welds and from the top down when making vertical welds. 



Underwater welds in mild steel plate develop 80 percent or more of the 

 tensile strength, but only 50 percent of the ductility of similar welds made 

 in air. This substantial decrease in ductility is explained by the hardening 

 resulting from the drastic quenching of the surrounding water. Because it is 

 not possible to preheat weld areas wet by water, to avoid cracking underwater 

 welding should not be attempted on base materials having carbon contents 

 above 0.25 percent or carbon equivalents (percent carbon plus 0.17 percent 

 manganese) above 0.40 percent. The area to be welded must be free from 

 marine growth, paint, mill scale, and rust to assure sound welds. Electric 

 shock is a hazard that must be taken into account by equipment and safety 

 procedures. Another hazard that could be overlooked is the possible explo- 

 sion resulting from the accummulation of hydrogen and oxygen gas in closed 

 or inadequately exposed compartments or spaces. Bubbles generated during 

 arc welding are about 70 percent hydrogen and are produced by electrolysis 

 of the water. Such accummulations of hydrogen can be ignited by spark or 

 flame. 



Underwater work including welding has been accomplished dry in air using 

 a caisson open to the surface. Such a structure must be strongly constructed 

 to stand the pressure of the water, approximately 9.8 kilopascals per meter 

 of depth (62.4 pounds per square foot per foot of depth), depending on salt 

 content and temperature. A caisson has been used to repair a tear 13.7 



216 



