Exothermic Electrodes

Figure 2-1. Underwater Oxygen-Arc Cutting Electrodes
Life Expectancy Underwater Welder
Figure 2-2. Underwater Oxygen-Arc Electrode Designs.

c. It serves as an electrical insulator, even in wet conditions, thereby assisting in safeguarding the diver in the event of accidental body contact while cutting.

d. It prevents arcing from the side of the electrode when working in confined quarters.

2-2.2.1 Advantages of the Steel-Tubular Electrodes. Steel-tubular electrodes have the following advantages:

a. The cutting technique is simple and readily mastered.

b. Metals up to 2 inches in thickness can be cut.

c. Cutting is performed rapidly.

d. Neat, trim, narrow cuts are produced.

e. The power required is within the capacity of a 400-ampere welding power supply.

f. There is less electrode waste because the electrode must be in constant contact with the metal being cut to sustain an arc.

2-2.2.2 Disadvantages of the Steel-Tubular Electrode. The disadvantages of the steel-tubular electrode are as follows:

a. The burning time of the electrode is short (approximately one minute).

b. It produces a narrow gap which may be difficult to locate in poor visibility conditions.

c. A welding machine is required.

d. The higher amperage requirement deteriorates electrode holder more rapidly than the exothermic process.

2-2.3 Electrode Amperage Requirements. The electrode amperage requirements for steel-tubular cutting are provided in Table 2-1.

Electrode

Current in Amps

Sea-Cut

300-400

Tuff Cote

300-400

The steel-tubular electrode requires 300-400 amps at the torch working depth. With proper power and oxygen pressure settings, satisfactory cutting results can be obtained. An amperage tong test ammeter is extremely useful in order to determine the exact amperage output of the welding generator. Do not rely solely on the values as indicated by panel control knobs or meters, as these are not always accurate. Simply encircle the welding lead with the tongs of the test ammeter and close them. A clear, accurate reading will instantly register on the scale. The tongs open by a slight pressure of one finger on the trigger and are self-closing. (See Chapter 4, Figure 4-9).

2-2.4 Oxygen Requirements. To ensure sufficient oxygen flow to the torch, a high volume, high flow regulator capable of delivering 70 CFM is necessary. A two-stage regulator is recommended. The cutting pressure must be 90 psi over bottom pressure. In Table 2-2, the regulator pressure settings are computed for the various oxygen lengths to a depth of 300 FSW. The formula used to calculate the oxygen values is provided following the table and may be used to determine oxygen requirements for depths and/or hose lengths not in the table.

2-2.5. Material Consumption. Table 2-3 is provided for planning purposes. It lists material consumption which can be expected while using steel-tubular electrodes during cutting operations.

2-2.6 Oxygen Pressure. Satisfactory cutting may be accomplished using a wide range of oxygen pressure settings; however, supplying less than optimum volume to the torch will decrease cutting efficiency, slow down the operation and unnecessarily fatigue the diver. On the other hand, too much oxygen for a given plate thickness wastes oxygen and increases diver stress by creating excessive back pressure at the electrode tip.

Hose length

Regulator

Hose length

Regulator

50 Foot

Pressure

100 Foot

Pressure

Depth

Setting

Depth

Setting

(FSW)

(psi)

(FSW)

(psi)

0

95

10

100

10

100

20

104

20

104

30

109

30

108

40

113

40

113

50

118

50

117

60

122

70

127

80

131

90

136

100

140

145

Hose length

Regulator

Hose length

Regulator

50 Foot

Pressure

100 Foot

Pressure

Depth

Setting

Depth

Setting

(FSW)

(psi)

(FSW)

(psi)

0

105

0

110

10

109

10

114

20

114

20

119

30

118

30

123

40

123

40

128

50

127

50

132

60

132

60

137

70

136

70

141

80

141

80

146

90

145

90

150

100

150

100

155

110

154

110

159

120

158

120

163

130

163

130

168

140

167

140

172

150

172

150

177

160

181

170

186

180

190

190

195

200

199

Hose length

Regulator

Hose length

Regulator

250 Foot

Pressure

300 Foot

Pressure

Depth

Setting

Depth

Setting

(FSW)

(psi)

(FSW)

(psi)

0

115

10

120

10

119

20

124

20

124

30

129

30

128

40

133

40

133

50

138

50

137

60

142

60

142

70

147

70

146

80

151

80

151

90

156

90

155

100

160

100

160

110

165

110

164

120

169

120

168

130

173

130

173

140

178

140

177

150

182

150

182

160

187

160

186

170

191

170

191

180

196

180

195

190

200

190

200

200

205

200

204

210

209

210

208

220

213

220

217

230

218

230

222

240

222

240

226

250

227

250

260

231

270

236

280

240

290

245

300

249

254

Hose length

Regulator

Hose length

Regulator

350 Foot

Pressure

400 Foot

Pressure

Depth

Setting

Depth

Setting

(FSW)

(psi)

(FSW)

(psi)

0

125

0

130

10

129

10

134

20

134

20

139

30

138

30

143

40

143

40

148

50

147

50

152

60

152

60

157

70

156

70

161

80

161

80

166

90

165

90

170

100

170

100

175

110

174

110

179

120

178

120

183

130

183

130

188

140

187

140

192

150

192

150

197

160

196

160

201

170

201

170

206

180

205

180

210

190

210

190

215

200

214

200

219

210

218

210

223

220

223

220

228

230

227

230

232

240

232

240

237

250

236

250

241

260

241

260

246

270

245

270

250

280

250

280

255

290

254

290

259

300

259

300

264

Example: To calculate required gauge pressure at any depth, use the following:

For every 10' of oxygen hose, add 1 psi to the 90 psi required at electrode tip. This compensates for frictional line loss. Additionally, add 0.445 psi per foot of depth to compensate for increased hydrostatic pressure.

i e., 10 + (0.445 x D) + 90 = Regulator Pressure Setting Where: H = Hose length (feet) D= Depth FSW 90 = Required psi at electrode tip

Unit

Steel Plate cut in ft/box of electrodes

1/4-in.

1/2-in.

3/4-in.

1-in.

plate

plate

plate

plate

50-lb.

240

170

170

160

Box of electrodes1

Oxygen cu.ft. per

594

440

440

440

box of electrodes2

1. Each 50-pound box contains approximately 167 electrodes.

2. There are approximately 220 cubic feet of gas in a standard oxygen cylinder charged to 2000 psi.

1. Each 50-pound box contains approximately 167 electrodes.

2. There are approximately 220 cubic feet of gas in a standard oxygen cylinder charged to 2000 psi.

2-2.7 Oxygen Purity. The oxygen purity for all underwater oxygen cutting should be 99.5 percent or 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 cutting should be 99.9 percent pure.

2-2.8 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 work site. The first task is to clean a spot for the ground clamp. The spot should be in a position in front of the diver and should be scraped or wire brushed shiny clean. For diver safety, only C-type clamps 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 when there 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.

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