Electrodes for underwater oxygen arc cutting are either tubular carbor- 

 undum or steel. Steel electrodes are available in 4.75- and 7.93-millimeter 

 (3/16 and 5/16 inch) diameters with a 1.6-millimeter-diameter Q/16 inch) 

 bore. These electrodes are provided with a waterproof coating, which serves 

 as an insulator during cutting. 



Cutting underwater requires that positive pressure be maintained by the 

 electrode against the metal being cut; whereas, in air, the electrode is 

 dragged along the intended line of cut. Particular attention must be paid 

 to safety. The power sources must be grounded to the tender and ground 

 cables securely connected to the work. All parts of the power cables and 

 torches must be fully insulated and periodically inspected. An operating 

 disconnecting switch must be part of the cutting electrical circuit. To 

 prevent possible explosions, enclosed spaces must be vented so that gases 

 generated during cutting cannot accummulate. 



3. Environmental Considerations . 



a. Exposure to Air . 



(1) General . In contrast to organic materials, sunlight exposure 

 does not cause deterioration of metals. Under some conditions, however, 

 sunlight can be a contributing factor in the stress corrosion cracking of 

 some stainless steels. Stress corrosion cracking occurs where high stress 

 accelerates corrosion along intercrystallinc boundaries, leading to weakening 

 of intercrystalline bonds and eventual cracking. Austenitic stainless 

 steels, such as type 304, 316, 321, 347, and even 216, are susceptible to 

 stress corrosion cracking when exposed simultaneously to heat, stress, 

 chloride ion, and oxygen. Cold-worked materials are most susceptible; 

 however, even annealed austenitic stainless steel contains some residual 

 stresses from fabrication and can crack. Stress corrosion cracking is 

 believed to be time dependent, but the exact threshold conditions for this 

 phenomenon to occur have not been established. Process equipment constructed 

 of austenitic stainless steel and hydrotested with seawater but not properly 

 drained and flushed has been ruined by stress corrosion cracking where the 

 only heat applied was the heat of the sun. 



(2) Effect of Severe Temperatures . At one time, harbor facilities 

 were located only in the torrid or temperate zones. Many ships were built of 

 riveted construction. Welded ships were constructed by fitting each plate 

 individually in turn. World War II created a demand for cargo ships that 

 only mass production techniques could meet. These techniques involved 

 constructing large hull sections off site, then moving them into position for 

 welding together to complete the hull. Because alinement of the sections 



was not perfect, force was applied to obtain sufficient alinement for welding. 

 Many of these ships broke in two in the North Atlantic. Investigations 

 revealed that brittle failure was the cause of these losses. Today, knowledge 

 of the relationship between notch toughness and brittle failure enables 

 marine structures to be designed to survive the most severe temperatures. 



Carbon and most alloy steels suffer a decrease in toughness as tempera- 

 tures are reduced. When slow rates of loading are applied these materials 

 exhibit increased tensile and yield strength with only a slight loss of 

 elongation and reduction of area at reduced temperatures. When the load is 



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