Exothermic Electrodes

Underwater Electrodes

Figure 2-23 Underwater oxygen-arc cutting electrodes.

There are two underwater thermal cutting processes currently approved for underwater use. They are:

• Shielded metal-arc cutting

• Oxygen-arc cutting with exothermic electrodes, steel-tubular electrodes, and Keri Cable

The shielded metal-arc underwater cutting process uses the intense heat of the arc to do the cutting. No oxygen is needed. It is the preferred method when cutting metal of 1/4 inch or less in thickness or when cutting nonferrous or corrosion-resistant metals of any thickness. The heat melts a localized area of metal forming a small molten pool. The pool will not flow enough to produce a good cut due to the rapid cooling from the quenching effect of the surrounding water. Therefore, the tip of the electrode must be manipulated to push the molten metal out of the kerf.

With oxygen-arc cutting the cutting action depends on the oxidation of a metal, such as steel, which oxidizes readily. Heat is applied with an electrode to a spot on the metal surface on the intended line of cut. When the metal is heated to a "kindling" temperature, a high-velocity jet of pure oxygen is directed at the heated spot and the metal oxidizes or burns rapidly, a process which takes place instantly. The high-velocity jet performs two necessary functions: (1) It produces additional heat by oxidizing the preheated metal, and (2) it blows the molten oxidized metal away.

The tip of the electrode, which is exposed to the effects of heat and oxi

Figure 2-23 Underwater oxygen-arc cutting electrodes.

rials such as concrete, rock, barnacles, and other sea growth. The electrode is 3/8 inch in diameter and 18 inches long. It will also fit the Arcair, BROCO, and the Craftsweld Torch.

The steel-tubular cutting electrode consists of a steel tube with a waterproofed flux covering. It is 14 indies long with a 5/16-inch outer diameter and a bore diameter slighdy under 1/8 inch.

A similar exothermic cutting method is the Clucas Thermic-Arc System (Kerie Cable). Unlike a rigid electrode, the consumable electrode is a long flexible spiral cable with the center strand pulled out to allow for oxygen to pass. The cable consists of six bundles of high tensile steel wire, which is encased in a plastic sheath. The Kerie Cable is applicable to all metal thicknesses and has a longer burn time than tubular electrodes. There is no electrical hazard after ignition.

For using the Kerie Cable, Table 2-10 provides oxygen pressure requirements; Table 2-11 gives cable size for metal thicknesses; and Table 2-12 provides estimated consumption rates for both cable and oxygen. The major disadvantages of using Kerie Cable are that it requires more oxygen than the other methods and it cannot be used to cut concrete or rock.

WARNING The Kerie Cable WILL NOT cut rock or concrete either above or below water. To attempt to do so may create an explosion causing injury or death.

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