UNDERWATER OXY-ARC BURNING
Diver and surface air/gas saturation supervisor John Roat of Legacy Offshore uses the exothermic cutting process during offshore repairs and construction. He identifies the risks involved in underwater burning and reviews the proper training and equipment that are essential to the safety of divers.
As a working diver and a surface air/gas saturation supervisor for the Legacy Offshore, LLC (Broussard, Louisiana) diving and construction company, John Roat spends a lot of time underwater serving the domestic and international oil and gas industries. He estimates that about 90 percent of underwater burning is done in these industries.
When conducting offshore repairs and construction, Roat often uses the exothermic cutting process which releases energy in the form of heat, and uses oxygen as an exciter and the steel rods become the fuel. As long as the oxygen flow is maintained through the torch and rod, the rod will continue to burn and consume at a temperature between 8,000 deg F to 10,000 deg F, and burn ferrous and non-ferrous materials such as concrete, rock, barnacles and other sea growth.
A knife switch is located on the tender platform so power can be turned on and off through commands given by the diver. By closing a knife switch, the tender completes the circuits and allows the torch to run ?hot?, or by throwing open the switch, the cutting or burning can be stopped and run ?cold.?
There are numerous potential risks involved in underwater burning such as electric shock and the build-up of pockets of hydrogen gas which are potentially explosive. Proper training and quality equipment are essential to the safety of the divers.
AN OXY-ARC BURNING TEST
The purpose of this example test is to compare three exothermic type burning rods with each other in three areas:
(1) Inches per rod in ¾ in, 1 in and 2-1/8 in.
(2) Consistence of rod burn.
(3) Cleanness of cut.
The exothermic rods being tested are the Broco 3/8, Arc-Air Sea Jet 3/8 and the Oxylance Aqua EXO 3/8 (see Figure 1). The Swordfish 5.0 x 450 mm, no oxygen rod is tested as well on ¼ in, 3/8 in, ½ in and ¾ in plate. All rods are compared to the standard set by Arc-Air Tuff Coat Tubular Steel Rod. The equipment used in this test is a 600 amp DC welder, burning, hot and ground leads constructed of 4/0 welding cable, 600 knife switch, Oxylance 5-500 O/2 Regulator high flow, Arcair Sea Torch cutting head. Terry Tatum and John Roat are the burners.
All three exothermic rods (AQUA EXO, Broco and Arcair Sea Jet) are comparable in inches per rod while burning thin steel up to 5/8 in burning cold. The Broco rod tends to go out, burn a little more erratic and leave more hangers than either the AQUA EXO or the Arcair Sea Jet. Figures 2-6 compare the three exothermic rods in ¾ in, 1 in and 2-1/8 in steel. Figures 2 and 3 are of 1 in and 2-1/8 in steel cut with Tuff Coat Tubular Steel Rods as a comparison.
In Figures 4-6, we experimented with each rod to give it its maximum travel. The Broco and Sea Jet where run at 300 amps, the AQUA EXO was run at 80 amps. All three rods had 100 psi at the torch head. The AQUA EXO and the Sea Jet both struck up easily and ran smoothly. The Broco was harder to strike up and when out more frequently and in general ran rougher and had less inches per rod.
AN ADDITIONAL EXOTHERMIC BURNING RODS TEST
In another test, the exothermic rods tested were the Broco 3/8, Arc-Air Sea Jet 3/8 and the Oxylance Aqua EXO 3/8. Three divers ? Matt Hoyt, Jennifer Wieben, and Justin Krahan, all having completed Burner 3 and been broken out in the last year ? were selected to test the rods. The equipment used included a 600 amp DC welder, burning, hot and ground leads constructed of 4/0 welding cable , 600 knife switch, Oxylance 5-500 O/2 Regulator high flow, Arcair Sea Torch cutting head.
The Broco and Sea Jet were run at 300 amps, the AQUA EXO was run at 80 amps. All three rods had 100 psi at the torch head. Comparisons:
(1) Inches per rod in ¾ in, 1 in and 2-1/8 in.
(2) Consistence of rod burn.
(3) Cleanness of cut.
Diver: Justin Krahn
(1) Inches per rod ¾ in steel: Aqua EXO 13 in; Broco 16 in; Sea Jet 20 in
(2) Inches per rod 1 in steel: Aqua EXO 12 in; Broco 13 in; Sea Jet 17 in
(3) Inches per rod 2-1/8 in steel: Aqua EXO 5 in; Broco 3 in; Sea Jet 9 in
(4) Consistence of rod burn: J. Krahn found the Sea Jet to be the most consistent rod followed closely by the Aqua EXO. The Broco rod became more inconsistent on the thicker steel.
(5) Cleanness of cut: J. Krahn found that the Sea Jet made the cleanest cut followed closely by the Aqua EXO with Broco having the most hangers/slag.
Diver: Jenifer Wieben
(1) Inches per rod ¾ in steel: Aqua EXO 8 in; Broco 9 in; Sea Jet 11 in
(2) Inches per rod 1 in steel: Aqua EXO 6 in; Broco 6 in; Sea Jet 10 in
(3) Inches per rod 2-1/8 in steel: Aqua EXO 3 in; Broco 3 in (with hangers); Sea Jet 5 in
(4) Consistence of rod burn: J. Wieben found the Sea Jet to be the most consistent rod followed closely by the Aqua EXO. The Broco rod became more inconsistent on the thicker steel.
(5) Cleanness of cut: J. Wieben found that the Sea Jet made the cleanest cut followed closely by the Aqua EXO with Broco having the most hangers/slag.
Diver: Matt Hoyt
(1) Inches per rod ¾ in steel: Aqua EXO 6½ in; Broco 8 in; Sea Jet 9 in
(2) Inches per rod 1 in steel: Aqua EXO 5 in; Broco 8 in (with hangers); Sea Jet 8 in
(3) Inches per rod 2-1/8 in steel: Aqua EXO 3 in; Broco 3 in (with hangers); Sea Jet 6 in
(4) Consistence of rod burn: M. Hoyt found the Sea Jet to be the most consistent rod followed closely by the Aqua EXO. The Broco rod became more inconsistent on the thicker steel.
(5) Cleanness of cut: M. Hoyt found that the Sea Jet made the cleanest cut followed closely by the Aqua EXO with Broco having the most hangers/slag.
All five divers testing the rods got more total inches from the Sea Jet rod. All agreed that the cleanest cutting rod was the Arcair Sea Jet, closely followed by the Aqua EXO. The Broco came in last in all categories. To conclude on the exothermic rods, Figure 7 shows the Arcair Sea Jet on the left, Broco in the center and the Oxylance AQUA EXO after being exposed to one week of weather. Note the heavy rust appearing on the Broco. There is none on the Sea Jet or EXO.
ANOTHER TEST: THE SWORDFISH NO O/2 ROD
The Swordfish is not a traditional burning rod. It would be better called a melting rod. Figures 8-10 show how it seems to work best when the melted steel can fall out of the cut. It requires much practice and visibility to use. ?I do not believe this rod could be used in black water (no visibility),? states Roat.
?We believe it could be used for light burning with visibility on thin steel items such as clamps, bolts, pipe with wall thickness of ½ in or less,? he explains. One problem encountered was melted steel filling in the cut on vertical cuts. The rod does create hydrogen in large enough quantity to be a vent problem. The gas bubbles from one rod where trapped and displaced a gallon of water from a two gallon container. The depth was minus 10 ft. This gas was of an explosive nature when presented with a flame.
Roat says that torches should be insulated electrically for safety and prohibit any oxygen leakage. Along with the torches, cutting rods play a critical role of in underwater burning, and have significant financial implications regardless the size of the project. Burners want rods that produce longer cuts, cleaner cuts, and have greater resistance to rust underwater. A veteran trainer, Roat recommends Arcair exothermic torches and burning rods. ?My favorite exothermic rod is the 3/8 Sea Jet. My favorite tubular steel is the Tuffcoat.?
Curt Wilsoncroft, the national specialist for Arcair, says the SeaTorch Combination Torch and ArcWater II Torch are popular torches because of their reputation for safety and performance. The rods are especially important, he explains, because no rust translates to fewer rods being wasted, increasing economic efficiency. There is very little acceptance for rust on a rod that is designed to be used underwater.
?Longer cuts will result in the need for fewer rods to complete each project as well as the conservation of valuable time starting and stopping and changing rods,? adds Wilsoncroft. ?Research has shown that one minute of time on dry land can be equal to that of seven minutes underwater, thus fewer rod changes, even though the changes are quick, can result in reduced labor costs and less money being spent on divers? equipment, specifically oxygen, leaving the client much more satisfied. Cleanliness of the cut can also save on labor and supplies by not requiring as much touch-up on jobs where it may traditionally be needed.?
Finally, Wilsoncroft notes that cut and burn consistency can help save as well providing a quicker cut and less time spent re-striking rods that won?t stay lit. He understands the dangers involved in all aspects of exothermic burning, especially when diving. ?Underwater burning requires training, practice and knowledge of what you?re burning,? he says. ?But with the proper manpower and equipment, we get unbelievably impressive results.?
– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
John Roat was a member of Underwater Demolition Teams 21, UDT 11 and SEAL Team 1. He went to work for Taylor Diving and Salvage the end of 1969 as a tender and broke out at Taylor Diving in 1970. He taught rigging, open tanks, harbor and burning for one year at the College of Oceaneering, and authored ?Oxy-Arc Underwater Burning Class?, a 90-minute training video and manual, for Oceans Technology. He can be contacted at JohnRoat@legacyoffshore.com.
Arcair is a brand of St. Louis-based Thermadyne Industries Inc., 16052 Swingley Ridge Road, Suite 300
St. Louis, MO 63017, 636-728-3057, Fax: 636-728-3021, www.thermadyne.com. Curt Wilsoncroft can be contacted at Curt_Wilsoncroft@thermadyne.com.