Underwater Cutting

WARNING

Serious injury or death may result when adequate precautions are not followed during underwater cutting or welding operations. Supervisors shall ensure that all personnel become thoroughly familiar with the safety precautions covered in Appendix D.

WARNING

Under no circumstances shall compressed air be substituted for oxygen in underwater cutting operations due to the danger of contaminating oxygen regulators and hoses with oil residue (hydrocarbons).

WARNING

The position of the ground in relation to the diver must be such that at no time does the diver or equipment become positioned between the ground and the electrode. The diver must avoid becoming part of the electrical circuit.

2-1 INTRODUCTION

One of the major tasks of the Salvor is the refloating of stranded vessels and the clearance of navigable harbor areas of wrecks and grounded ships. Most often this requires the use of underwater cutting equipment. This chapter presents detailed technical information and procedures to be used while engaged in underwater cutting operations. As previously mentioned, there are two methods of underwater cutting currently being used: oxygen-arc and shielded metal-arc cutting. Each method is discussed in this chapter.

2-2 OXYGEN-ARC CUTTING

There are two types of electrodes used for oxygen-arc (oxy-arc) cutting—steel-tubular (manufactured by Arcair) and the exothermic types (Arcair's Sea-Jet and BROCO's Ultrathermic - see Figure 2-1). These electrodes provide excellent cutting results and can be used with a constant current DC welding generator set on straight polarity (electrode negative) supplying current to the electrode. With the work grounded, the electrode will ignite as it touches the work. Oxygen-Arc is preferred because it cuts plain and low-carbon steel easily.

2-2.1 Principles of Operation. Oxygen-arc cutting is defined as an oxygen cutting process in which metal is severed by means of the chemical reaction of oxygen with the base metal at elevated temperatures. The heat of the arc brings the metal to its kindling temperature, then a high velocity jet of pure oxygen is directed through a tubular cutting electrode at the heated spot. The metal oxidizes and is blown away. The tip of the electrode, which is exposed to both heat and oxidation, is consumed in the process and must be replaced frequently.

2-2.2 Steel-Tubular Electrodes. The steel-tubular electrode consists of a steel tube with a waterproofed flux coating which is applied during the manufacturing process. The electrode is 14 inches long with a 5/16-inch outer diameter and a bore diameter of slightly less than 1/8 inch (see Figures 2-2a and 2-2b).

The waterproof flux coating is similar in composition to the coating on welding electrodes. The flux coating serves the following purposes:

a. It promotes easy starting and maintenance of the arc.

b. It liberates gases, thus forming a protective bubble around the arc.

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