The underwater welding process seems to defy logic:
How does electricity flow through water leaving the underwater welder unscathed?
As you might guess, there’s a lot more to it. Here’s a few factors to think about:
- Underwater welding works in a similar fashion to topside welding, though the environment is different.
- Underwater welders take on risk, but not as much as you might think.
- The underwater welding process is misunderstood, leaving open-ended rumors and explanations that aren’t always true.
Before you understand how underwater welding works, it’s important that you get the basics of surface welding.
The Big Melt: How Topside Welding Works
A worker can do this by using one of several ways:
The list goes on, but these are the most well-known types of welding.
For simplicity’s sake, we’re going to focus on SMAW, more commonly referred to as “stick welding”.
Stick Welding Equipment: Decked Out
In SMAW, the welder uses three pieces of equipment:
- Welding Machine: Supplies the power to the electrode.
- Electrode Holder/stinger: Controls the electrode’s movement and connects to the welding machine.
- Electrode: A long rod that is composed of metals and coated with a flux, which is released when heat is applied.
Surface Welding Process: Firing it Up
The welder applies the electrode tip close to the base of the weld site where the two metals will need to be joined. When the welding machine is turned on, an electric current flows from the electrode to the weld site. The welder moves the electrode along the entire seam of the weld site, allowing the electrode to melt and fill in the gap, much like stopping up a river by filling it with dirt.
Since oxygen is corrosive to the weld site, engineers and chemists have developed special mixtures of chemicals on the electrode flux. When heat is applied, these chemicals mix with the air and create a temporary gaseous shield around the weld site while it’s being welded.
This shield protects it from becoming brittle.
Welding, Melting and Cooling: Where the Heat Goes
Welding uses a lot of heat. Over 6,500°F when applied to the weld site.
The heat is generated and moved in several areas:
- Anode: Weld site (positive charge)
- Plasma: Proximity surrounding the electric arc and weld site (gateway)
- Cathode: Welding rod (negative charge)
As you may learned from chemistry, molecules tend to move to the opposing ends of their charge (polarity).
When the plasma is created (through the welder’s electric arc), negative electrons move down toward the anode. Transversely, the ions from the anode move up toward the cathode.
All this happens instantaneously.
The majority of the heat remains in the anode, but some stays back in the cathode.
Underwater Welding Process: Working 2 Types
Think the underwater welding process. What comes to your mind?
Probably an underwater welder in a dive suit, surrounded by water and firing electricity at a metal gap in need of repair.
He’s performing one type of underwater welding: wet welding
There’s also another type: hyperbaric welding
These two types each have a slightly different underwater welding process, so we’ll look at each one. Both take on the same principles as surface welding, but utilize them in slightly different ways.
About Wet Welding: An Ocean of Learning
In wet welding, the diver’s weld site is surrounded by water.
This creates a challenge for welders, since the oxygenated water can make the weld brittle and porous. But a strong weld can be achieved. In fact, some companies are now able to create Class A (considered permanent) welds in wet conditions.
Underwater Wet Welding Process
Wet weld sites are surrounded by water.
But that doesn’t mean they’re directly exposed to the water during the welding process. Stick welding creates a gaseous bubble that keep the weld site temporarily shielded (primarily made of hydrogen).
This shield is created from the flux when it melts around the electrode. It’s made of about 70% hydrogen.
As the flux melts, it covers the weld site to protect it from water during the cooling process. However, even with this protection, water still has an effect on the weld.
Also, because the electric arc creates tremendous amounts of heat, it sprays up thousands of bubbles while the weld is in progress. More than an annoyance, these bubbles sometimes blind the underwater welder making it impossible to see the weld site.
As underwater welders progress in skills, limited visibility becomes less of a problem.
They can approximate the weld distance, penetration and other factors based off of other wet welds they’ve done.
Underwater Wet Welding power system
Wet welding uses a doubly insulated wires from the welding machine to the stinger (electrode holder). It also uses a knife switch to cut or open power. It also uses only direct current.
Hyperbaric/Dry Welding: Inside the Pressurized Room
In hyperbaric, or dry welding, the underwater welder’s weld site is insulated from water. This insulation is accomplished through a physical barrier filled with gas. Let’s go more in-depth to see what’s involved:
Underwater Dry Welding Process
The process is almost identical to topside welding, with a few exceptions:
- Hyperbaric welding takes place at higher pressures. To be exact: 0.7% pounds per square inch more. The pressure must increase to keep the air volume at a constant, set ratio to that of the surrounding water.
- Hyperbaric welding takes place in a pressurized, underwater habitat. The habitats may fit just around the weld site or expand to the size of a small room.
- Hyperbaric welding can be crazy expensive. The larger habitats cost a lot of money in the initial purchase and upkeep. In addition, the maintenance while in use also racks up the bills, since it’s supplying constant gas and electricity to the welders.
Cable System in Underwater Dry Welding
Dry welding uses either alternating or direct current (similar to topside welding). It also has a single insulation system for the power cables. The knife switch isn’t necessarily incorporated into the model.
Knowledge of the Underwater Welding Process
Underwater welding has a reputation for danger, but like many other subjects, the primary danger is lack of understanding. I hope this has created more transparency for you to better understand the underwater welding process.
If you have questions on either wet or dry underwater welding, please let me know in the comment section below.