Welding Works Underwater Because of a Bubble
By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Amanda McCallister, editor.
Underwater Welding & Cutting | Cathodic Protection & Anodes August 1987, Dardanelle Dam, Arkansas River. I was 19, a tender on a five-man dive crew. We were there to pin a broken gate hinge on a downstream lock. The water was warm, brown, and full of silt; you couldn't see your hand past the faceplate. My boss, a guy named Pops, told me I'd be laying the weld that afternoon. I remember thinking he was about to fire me. I climbed over the gate, hung off the ladder, and let myself sink. It got dark before I reached the work site. I found the broken hinge by feel, took the rod from my belt, and bit down on the stinger. When I hit the trigger, the water around the rod turned into a silver bubble. I'd never seen anything like it. That bubble is why I've been doing this for 28 years. Here's what most people don't understand: you can't weld underwater. Not really. You weld inside a gas bubble. The water doesn't stop the arc because it's not in the way. The welding electrode burns off a fancy chemical coating that turns to gas. That gas pushes the water back, giving the arc a dry, quiet pocket to work in. The weld metal is laid down inside that pocket. The water then flows in behind as the bubble collapses, cooling the weld in a hurry. The bubble is the only reason any of this works. Since then, I've taught the same lesson to dozens of divers. A lot of them want to skip it and just turn up the amperage. That's a mistake. If you don't understand the bubble, you can't keep it alive. And if you don't keep it alive, you're just burning rod in a river. So here's a quick course: where the bubble comes from, how you hold it, and what can go wrong.
Where the Bubble Comes From
It's not magic, it's chemistry. A wet welding electrode is a steel core wrapped in a thick coating of flux. That flux contains minerals, cellulose, and often iron powder. Underwater, we add a waterproof top layer to keep the flux from dissolving before you use it. When you strike the arc, the flux burns. It breaks down chemically and releases a mix of gases, mostly carbon monoxide and hydrogen, plus some oxygen. These gases expand and form a continuous envelope around the arc. The pressure from the gas is higher than the surrounding water pressure, so it holds the water back. The bubble is like a mini welding umbrella. The arc burns inside it, and the molten metal fuses into a weld puddle. The coating does double duty: it creates the bubble and it shields the molten metal from oxygen and nitrogen, which would make the weld porous and weak. In wet welding, the electrode is usually a low-hydrogen type with a special designation. You'll see it in the AWS D3.6 spec, which is the underwater welding code. And it's got to run on direct current, electrode positive. That setting gives you enough arc force to keep the bubble from collapsing in the water's current.
How to Hold It: The Technique
The rod is your bubble gun. If you pull it off the surface, the basket of gas lifts off the steel and the water immediately floods in. So the first rule is: keep the arc short. That means dragging the rod at the surface, not holding it in the air. There's a feel to it. When the bubble is right, the arc hisses steadily, like bacon frying. You'll see a bright blue-white glow through your welding hood. The water around you is steaming and sputtering, but you're working in that dry pocket. Second rule: keep your rod perpendicular to the joint, tilted maybe 5 or 10 degrees in the direction of travel. That lets the bubble push away the water from the joint, not just up. Third rule: don't weave. A wet weld isn't the place for a fancy pattern. It's short, straight, overlapping beads. Each bead is its own bubble. You lay one, bang off the slag, and start the next. If you let the bubble collapse, the arc stops and you're back to blinking at the surface. On that lock gate, I had to learn to trust the hissing. I burned about half a dozen rods before I figured out I didn't need to push the rod out of the water bubble. I just kept it planted.
The Kit That Makes It Happen
A wet weld starts on the surface. You need a DC welding machine, usually a 300-amp engine drive calibrated to a low enough voltage. We run a 6013 or a 7018 electrode with a waterproof coating, though the specs are different for underwater. The stinger is a heavy-duty o-ring sealed handle, so the water can't short out the connection. The cable is a copper, rubber-jacketed lead that runs all the way from the machine to the stinger. The diver wears a thick rubber glove over the bare hand, and a second glove under it for insulation. You also need a welding hood that looks like a chainmail visor with a glass plate, so you can see the arc without lighting your eyes up. And you need a dive mask that doesn't trap air in front of your eyes -- the bubble will make it fog in seconds. You'll also need a weighted 'boot' on the rod to keep it from swimming away. The whole system has to be set up so you never touch the live metal with your skin. If you do, you electrocute yourself inside an arc. That's not a metaphor.
The Hidden Dangers
The bubble is a safe space, but it's not a magic shield. The water absorbs and quenches the weld bead immediately. That rapid cooling turns the steel's microstructure into martensite, a very hard, very brittle phase. It's like glass in metal form. It can crack just from the stress of cooling. And the bubble is rich in hydrogen, an enemy of steel. Hydrogen atoms can get trapped in the weld and cause cracking hours or days later, a process we call hydrogen-induced cold cracking. That's why we use low-hydrogen electrodes and why we grind each weld pass down to clean metal before the next pass. It's also why we often do a temper-bead pass: we put a low-grade heat bead over the weld to refine the grain structure and make it tougher. That's a technique you learn slowly, and your first big weld will probably teach it to you. I've seen a diver blow a pin because he didn't grind his root pass, and the weld was full of pinholes. The client didn't care about the reason. So the practical lesson: always inspect your weld, always grind, and always, always keep your bubble alive. I've got a small scar on my forearm where a stinger shorted against my drysuit. You don't forget that.
Frequently Asked Questions
Is underwater welding safe? It's a trade that has gotten safer with training and gear. The ADCI sets standards, and the diver must be qualified for both diving and welding. You work with a tender on the surface, you use low-voltage controlled by the machine, and you follow the code. It's not safe without that training. But with it, it's one of the most rewarding careers in the water. How deep can you do wet welding? As depth increases, the gas bubble shrinks because of the pressure. At some point the arc won't hold, so we keep wet welding to shallow or moderate depths. For deep repairs, we use a dry hyperbaric chamber, where the welding happens in a sealed, pressurized habitat rather than in direct water. Can you see what you're doing underwater? Not like you'd think. The bubble is full of gas and the water around it turns to a cloud of boiling silt. You actually weld by feel, listening to the hiss, reading the light through your hood. It's like welding in a snowglobe. You have to trust your hands.