Underwater welding is the act of welding together two pieces of metal underwater, typically at very high pressures. As fire is obviously not an option, underwater welders use electricity to melt and combine pieces of metal to one another.
Underwater welding, or hyperbaric welding, uses electricity to weld pieces of metal together. How can this be possible? After all, isn’t mixing electricity and water dangerous? It can be, which is why hyperbaric or underwater welders have to take special precautions when welding.
When electricity is suspended in a fluid, it can behave very unpredictably. Electricity is dangerous when it can move between two conductive surfaces and follow a path, and we use insulated solid surfaces such as copper to control it. However, in the water, there isn’t a specific path for electricity to pass through which means that it just finds the path of least resistance. The path of least resistance can be through a person, so welding underwater can be dangerous if the proper precautions aren’t taken.
How Underwater Welding Works
Underwater welding is often done by applying heat generated by an electrode to the target area. The distribution of the heat from the electrode is influenced by charged electrons. This is referred to as Shielded Metal Arc Welding. There are essentially three different components that influence how the heat moves while welding: the anode (or target weld area), the cathode (the electrode) and the plasma the process generates and through which the electricity travels.
Since the anode is positively charged and the cathode is negatively charged they make a channel through which electricity can flow. Positive ions will move from the anode to the cathode, while the electrons travel the opposite way, from the cathode to the anode. The welding circuit is completed when the welder strikes an arc, and the heat of the arc coming to life vaporizes the water in the surrounding area. The sheer amount of movement in the particles generates a massive amount of heat, heat energy at more than 5,000 degrees Celsius exists at the connection between the anode and cathode.
Dry Welding Underwater
Underwater welding can be done in a number of ways. One of the ways underwater welding is done is by constructing a “hyperbaric chamber”, an enclosure of dry air that welding can be done in underwater. The chamber is pressured, similar to a submarine. Like diving bells, a system of pumps and fans is controlled by a surface crew, and an enclosed chamber is used to provide a continuous volume of air for the divers. The chamber is engineered to function at only .007 psi above the normal atmospheric pressure outside the chamber. Essentially, a giant air bubble is constructed that is lowered beneath the surface of the water, which allows the divers to work on their welding in a dry habitat.
The air is cycled in and out of the chamber, which means that the toxic fumes created by the act of welding are sucked out while new air is pumped in. This prevents the welders from suffocating. At particularly high pressure, dive teams may employ helium for the purposes of pressurization. Helium’s light weight means it helps the chamber withstand the pressure so that the welders don’t develop conditions like nitrogen narcosis or pass out. A dry welding habitat can hold up to three people.
Large diving habitats are typically only employed in the construction of major projects, as they tend to be very expensive and labor intensive. However, small diving habitats created to just fit over a person’s upper body also exist, and they are comparatively cheaper. Finally, there are also portable habitats that enclose just the electrode in the welding gear, which come with the added benefit of not needing a constant supply of fresh air.
Wet Welding Underwater
While the above forms of underwater welding are known as “dry welding”, “wet welding” methods also exist. The preferred type of welding in dry welding habitats is a method called “gas tungsten arc welding”, which utilizes a tungsten-based electrode to initiate a weld. While almost any type of welding can be employed in a dry welding habitat, underwater welders are restricted primarily to the use of shielded metal arc welding (SMAW).
While SMAW underwater welding is considered to be easier than dry chamber welding, it is also more dangerous. The level of electricity used by the welder must be monitored carefully, and all the equipment used in wet underwater welding must be properly insulated, or the diver risks electrocution. Wet underwater divers also risk building up levels of hydrogen and oxygen gases which can explode. Then there are the normal hazards associated with diving, such decompression sickness thanks to the breathing gases increasing pressure in the body.
Waterproof electrodes are utilized during wet underwater welding, and wet welds are done with a gaseous bubble around the arc of the welding device. The shielding bubble is usually composed of hydrogen, carbon monoxide and carbon dioxide. This is accomplished by coating the waterproof electrodes with a material known as “flux”, which produces the gas bubble as the electrode heats up.
The pressure of the bubble must be maintained at a precise level, with attention paid to where the electrode is from the surface of the object being welded. As the pressure within the gas bubble increases it is shoved out from under the arc and into the water, while another bubble formed by the gasses takes its place. If the electrode is being operated too far from the surface of the work, the gases will explode and push through the weld. The bubble shield is only found right around the weld itself.
The welding of two surfaces underwater creates unintended additional air bubbles that fly into the water surrounding the diver. This means that underwater welders often struggle with visibility. Furthermore, the bubbles created by these welds impact the arc generated by the electrode, which means the arc is at risk of collapsing and ceasing to function. Experienced welder must learn how to overcome the challenges.
As the welder moves around welding the seam of the two surfaces together, they create a hot liquid metal referred to as “slag”. The function of this slag is that it protects the seam so the weld can properly cool and form the two surfaces together. Unfortunately, the slag sometimes dropped in unintended places, which can cause problems like imperfections in the welding surfaces. To get around this, engineers have created a superior type of flux that burns more consistently on the electrode and lets welders drip slag more evenly and consistently.
Underwater welding is a complex and sometimes dangerous process, but if it didn’t exist there would be no way to repair marine structures like pipelines, ships or offshore platforms.