There are many offshore structures such as oil drilling rigs, subsea pipelines, and offshore platforms built underwater, and they all need underwater welding during their construction and post-construction maintenance. Such welding jobs executed under the water are called ‘underwater welding,’ and the professionals who do the welding jobs under the water are called ‘underwater welders.’
This article takes you through the following topics: what underwater welding is, how does underwater welding works, the welding processes used for underwater welding, saturation divers and saturation chamber, welding equipment for underwater welding, what are the risks and safety considerations, and application of underwater welding.
What is underwater welding?
When you do welding at elevated pressure under the water, such welding is called underwater welding. You can do the welding directly underwater (called wet welding) or inside a specially fabricated enclosure placed under the water (called dry welding). So, you can define underwater welding as welding done underwater and at elevated pressures.
The welding which is done on the land and that done underwater follows similar technology; however, an underwater welder has to work submerged deep under the water, at elevated pressures, adverse conditions, and inbuilt dangers associated with this profession. Hence, strict safety precautions are very important.
The difficulties faced by an underwater welder are elevated pressure, low temperatures (depending on the depth), poor visibility, strong water currents, and also reduced quality/strength of the welds.
Related article: Underwater Welding Death Rate
Types of underwater welding
Underwater welding can be divided into two basic categories dry underwater welding and wet underwater welding. Both dry underwater welding and wet underwater welding are done underwater; however, dry underwater welding is done in a safe enclosure.
Dry underwater welding
When underwater welding is carried out in a specially fabricated enclosure called ‘habitats’ (hyperbaric chamber/enclosure) placed under the water, it is called dry underwater welding.
Dry underwater welding is also called hyperbaric welding since the welding process is performed at elevated pressure in a sealed chamber filled with a mixture of gas (normally helium and oxygen). Most welding processes such as shielded metal arc welding (SMAW), flux-cored arc welding (FCAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), plasma arc welding (PAW) could be performed at hyperbaric chamber; however, GTAW (gas tungsten arc welding) is typically used for dry underwater welding.
A hyperbaric chamber specifically made for the welding work on hand is lowered into the water (location of the work). The water is pumped out, and the space in the chamber is filled with a gaseous mixture, helium, and oxygen. The hyperbaric chamber is pressurized to the correct level to prevent decompression sickness.
Presently dry hyperbaric welding is limited up to 400 meters (1312 feet) of water depth, and experiments are in progress for increasing the depth. The limitations are the physiological capability of underwater welders to operate the welding equipment at that pressure and the construction of a hyperbaric chamber for such water depths.
Advantages of dry underwater welding
- The dry habitat is warm and comfortable, and the underwater welder is safe from dangerous water animals and ocean currents.
- In the absence of water to quench the weld joint, the cooling of the weld joint takes place properly, and the weld joint is free of cracks. The welder has good visibility of the work.
- Non-destructive testing (NDT) can be undertaken, and welding defects can be corrected.
- The work done by the underwater welder can be monitored visually by the onshore staff.
- Dry underwater welding is preferred where there is a need for good quality welding, and the work location is at a higher depth.
Drawbacks of dry underwater welding
- Hyperbaric chambers take time to plan and arrange.
- The process is extremely costly since the chambers are unique for each job and cannot be reused.
- The support staff and equipment on the surface are costly.
- With the increase in depth, the arc requires a higher voltage.
- Dry underwater welding cannot be adopted in case of emergency or breakdown.
Wet underwater welding
When you carry out the welding in a wet environment, deep under the water, it is called wet underwater welding. The underwater welder dives into the water wearing the diving gear and does the welding.
Wet underwater welding brings the welder, the underwater welding rod, electrode holder, electric cables, and other equipment to direct contact with water. All these accessories, including the underwater welding rod, are insulated and waterproof. The underwater welder wears thick rubber gloves. The DC source kept at the surface supplies of 300 to 400 amps current.
Wet underwater welding is the only option to deal with an emergency. The main issues connected with wet underwater welding are the risk of doing welding underwater, the welding done in an environment of water makes the weld joint cool fast, which may lead to quality issues such as welding cracks, and finally, the quality of weld joint also depends on the approachability of the part to be welded.
Advantages of wet underwater welding
- Wet underwater welding is more versatile than dry underwater welding and the cost incurred is less.
- Wet underwater welding can be done fast and is the only method during an emergency.
- Wet underwater welder can access parts of the underwater structures and pipelines, which cannot be accessed by dry underwater welding.
- No enclosures are needed, and the welding equipment can be mobilized faster.
Drawbacks of wet underwater welding
- Rapid cooling of the weld joint affects its strength and ductility.
- Poor visibility in the water.
- The underwater welder is exposed to ocean currents and other threats.
- The integrity of the welding done by wet underwater welding cannot be guaranteed since there is no means to inspect and ensure it. Much depends on the skill of the underwater welder and the technic adopted.
- In wet underwater welding, there is a risk of non-detection of welding defects.
How does underwater welding works?
Let us consider the process of wet underwater welding first; a kick-off meeting is held between the project team and the underwater welder to discuss the work on hand in detail and conclude the method and underwater welding process and ensure that everyone is aware of the project details.
The current requirement for underwater welding is typically 300 to 400 amperes, and only DC current is used. All the accessories such as connecting cables, electrode holder, and underwater welding rods are waterproof and properly insulated to ensure there will not be electric leakage when they are used underwater. It is always preferred and safe to do trial welding in water to ensure the safeness of these accessories.
SMAW (shielded metal arc welding) process with a waterproof underwater welding rod is typically used in wet underwater welding. The underwater welder wears his diving and safety gear and dives into the water to the location of work.
The work is connected to the positive (+) terminal of the DC source and the electrode holder to the DC source’s negative (-) terminal. The connection to the work is typically made with a C-clamp. The underwater welder selects a location nearer to the weld joint, cleans and shines it with a wire brush, and clamp the C-clamp firmly to the workpiece. The underwater welder may lightly tack-weld the C-clamp to the workpiece, if necessary.
The underwater welding brings the welder, the welding electrode, and the welding accessories to the direct contact of water. The electrode holder is heavily insulated and specially designed for water cooling, and the underwater welder wears electrically insulated hand gloves.
The connection from the DC source to the workpiece and the electrode has a heavy-duty knife/isolation switch in the circuit monitored by the staff on the surface (ship). The underwater welder can communicate with the team on the surface (ship). The isolation switch remains disconnected all the time except during welding and connecting the work. The electrode holder with the DC source is switched on by the staff on the surface, only on the instruction of the underwater welder. As an underwater welder, you will be communicating with the surface staff on the ship deck from the moment you dive into the water to the moment you complete the work successfully.
When ready for welding, the underwater welder instructs the staff on the surface to close the knife switches and does the welding. He/she advises the surface team to disconnect the switches for changing the electrode or during breaks. Usually, there will be established commands to connect or disconnect the electric power. One such command can be ‘make it hot’ (for connecting the work & electrode holder to the DC source) and ‘make it cold’ (for disconnecting).
The electric arc between the work and the welding electrode heats the workpiece and the welding rod. The workpiece is connected to the positive terminal and the electrode holder to the negative terminal; this ensures 60% of the heat generated goes to the wok and 40% to the electrode. The arc generated in water creates gas bubbles (hydrogen, carbon dioxide, and carbon monoxide), which protects the weld joint. The coating of flux on the electrode melts and gets deposited as a slag on the welded joint. The slag protects the weld joint and reduces the rate of cooling. The production of bubbles obstructs the visibility of the welding to the welder; however, a good welder knows how to manage this. The deposition of slag on the weld joint helps slow the cooling rate; however, rapid cooling of the weld joint is a major obstacle in ensuring a crack-free weld joint.
An underwater welder is expected to accomplish his/her work in difficult and challenging situations. The technique of underwater welding is equally beneficial for both inland water and offshore sites. Doing the welding process on land is not the same as doing welding underwater, and all the welding techniques used on land may not be adaptable for underwater welding.
Few underwater welding jobs, like the repair of ships, are carried out in shallow depths, and other welding jobs such as pipelines and structures are carried out deep under the water.
Dry underwater welding process, in the dry underwater welding, the habitat or the hyperbaric chamber is lowered into the work location and made ready for the underwater welder to do his work. Since the dry underwater welding is done in a dry ambiance, DC or AC current can be used, and GTAW (gas tungsten arc welding) is generally used for dry underwater welding.
The underwater welder wears his diving and safety gear, dives into the water, reaches the work location, and enters the hyperbaric chamber. He/she will take out the diving suite and starts the welding work. The welder breathes the mixed gas helium and oxygen. In some cases, when the depth of the location is more, the underwater welder may travel in a small chamber (diving bell) from the surface to the hyperbaric chamber.
Overall degradation of welding in terms of capability and efficiency is found to happen at elevated pressures.
Welding processes used for underwater welding
Wet underwater welding
Commonly Shielded Metal Arc Welding (SMAW) is used for wet welding. SMAW process is versatile, cost-effective, and is easy for the underwater welder to strike an arc between the welding rod and the work.
Flux Cored Arc Welding FCAW-S (self-shielding) process contains a flux that protects the weld pool. FCAW-S process may be used for cast iron, nickel alloy, and other metal alloys. The consumable electrode has a tube filled with flux at the center. The electrode in the form of a wire is fed automatically.
Welding processes like Gas Tungsten Arc Welding (GTAW), also known as TIG (tungsten inert arc welding), Gas Metal Arc Welding, also known as MIG (Metal Inert Gas welding), etc. uses inert gas to shield the weld joint and hence cannot work under the water.
Dry underwater welding
Gas Tungsten Arc Welding (GTAW), also known as TIG (tungsten inert arc welding) is typically used for dry underwater welding because of its good quality welding and its ability to perform at elevated pressures (underwater). The underwater welder uses the tungsten electrode to melt the filler wire, and the molten metal is deposited on the weld joint. TIG welding produces a quality weld joint.
Flux Cored Arc Welding ((FCAW-G (gas-shielded)), Gas Metal Arc Welding (GMAW), also known as MIG (Metal Inert Gas) welding, and Plasma Arc Welding (PAW) can also be used for dry underwater welding; however, they do not perform well at elevated pressures. Shielded Metal Arc Welding (SMAW) is not preferred due to the fumes/smoke it generates.
Saturation divers and saturation chamber
A capsule of approximately 15-16 feet ×7-8 feet is built in a ship and is maintained at 18-19 times more pressure than the atmospheric pressure, which is called the saturation chamber. This saturation chamber is home for typically six men who eat, work, play, rest, and sleep here for 28 days at a stretch. The men are saturation divers who work for the company engaged in underwater welding at a depth of 500+ feet.
When an underwater welder dives into the deep water, the elevated pressure compresses the gases like carbon dioxide and nitrogen in his blood/tissues. He is fine as long as he stays in that depth; however, at the end of the working day, if he comes up to the surface fast, the compressed gases in his blood/tissue try to expand, resulting in ‘bends’ which is very painful. After returning to the surface, the diver may take 5-6 days of rest/decompression before resume his work. This means that the company has to pay for six days for the work of one day. This is not an economic proposition. Hence, the idea of a saturation chamber has come up.
This system keeps the underwater welders (called saturation divers) at the same pressure throughout the day for 28 days. The saturation chamber on the ship is maintained at the same pressure as at the work location (at a depth of 500+feet).
A pressurized diving bell takes the saturation diver from the saturation chamber to the work location. After completing the shift of the saturation diver, the diving bell takes the saturation diver back to the saturation chamber in the ship. This will continue for 28 days, and after 28 days, a new batch of 6 men will replace the old batch. The six men in the saturation chamber can work in shifts.
Welding equipment and tools for underwater welding
Equipment for wet welding
The underwater welder needs two types of equipment, diving equipment, and welding equipment. Welder safety is the major criteria for choosing this equipment, and the equipment must meet all the set safety standards. The complete equipment should undergo regular maintenance as per the laid-out standards.
The diving equipment includes a diving helmet, diving knife, umbilical cord, harness, gas panel and compressor, bailout gas, diving suit, and rubber hand gloves.
The underwater welding equipment includes a DC power source, underwater electrodes, waterproof and heavily insulated electrode holder (stinger), C-clamp to connect the positive terminal to the workpiece, waterproof and heavily insulated cables connecting the DC positive terminal to the workpiece, and the DC negative terminal to the electrode holder, knife switch, communication system between the underwater welder and the ground staff, and miscellaneous tools chisel and chipping hammer.
Diving equipment
- Diving helmet – A diving helmet is used by the underwater welder when he/she goes under deep water. This helmet allows breathing for the underwater welder and has a welding screen in the front, which protects the eyes during underwater welding. The welding screen can be flipped to open or close.
- Diving knife – A diving knife is a multipurpose tool, and the underwater welder can use this to free himself/herself from a critical situation or wedge open a door, etc.
- Umbilical cord – This is used for supplying the breathing gas from the surface to the underwater welder.
- Harness – A harness is used to keep the underwater welder floating at one place during welding.
- Gas panel and compressor – This is located at the surface and is continuously monitored by the surface staff to ensure a continuous supply of breathing gas to the underwater welder.
- Bailout gas – This is like a small scuba tank available with the underwater welder for emergency use.
- Diving suit – Underwater welders must wear a dry-suit to protect themselves from the climatic condition under deep water. Depending on the depth of work location and the environment, the dry-suit can be of neoprene, rubber, or shell. Some underwater welders wear a cover-all over the dry-suit to protect against molten weld metal falling on their body.
- Rubber hand gloves – An underwater welder wears a pair of latex hand gloves and thick rubber hand gloves (over the latex) to protect himself/herself from electric shocks. The design of the hand gloves should be such that it does not allow the water to enter into the underwater welder’s body.
Underwater welding equipment
- DC Power source– The power source should be a Direct Current welding generator capable of 300 to 400 amps on 65 Volts open circuit. The equipment DC circuit must include a circuit breaker.
- Underwater electrodes– The electrodes used for underwater welding are extremely resistant to water, highly insulated, flux coated, and have a high yield strength. All these properties are necessary for safe and good quality underwater welding.
- Waterproof and heavily insulated electrode holder (stinger) – The electrode holder for underwater welding should be highly insulated, water-cooled, ergonomic and lightweight, properly angled so that the underwater welder can use it safely and without much strain.
- C-clamp – to connect the positive terminal to the workpiece.
- Waterproof and heavily insulated cables – connecting the DC positive terminal to the workpiece and the DC negative terminal to the electrode holder, the cables should be of excellent quality. Each of these cables has a knife switch at the surface (ship) and is controlled by the surface staff.
- Knife switch – A knife switch is a simple switch used by the surface staff to connect or disconnect the DC power to the electrode holder and the work. The knife switch is in the disengaged (disconnected) position at all times except during welding. The surface staff connects the knife switch only after receiving a clear communication of ‘make it hot’ by the underwater welder.
- A communication system between the underwater welder and the ground staff – The communication system should be of good quality and should be able to work in the underwater environment.
- Miscellaneous tools such as chisel and chipping hammer.
Associated risks and safety considerations
Let us consider the risks first
- Professional underwater welders must work in intimidating environments, deep under the water, at elevated pressures, and often with poor visibility.
- Water is a good conductor of electricity, and an underwater welder has the danger of shocks/electrocution.
- Decompression sickness (also known as ‘the bends’) may happen when the underwater welder moves up to the surface very quickly. The symptoms of decompression sickness are fatigue, itching, headache, loss of appetite, etc. Underwater welders can use specially designed diving gears, ascending with decompression stops, and decompression chambers to overcome the sickness.
- Hypothermia, underwater welders spend more time under the water and may lose their body temperature fast, leading to hypothermia.
- The lungs, ears, and nose’s functions can be affected due to the elevated pressure under the water.
- The underwater welder wears heavy diver gear, and this, along with the noise created during the work, usually acts as a deterrence for the shark attack.
Some of the risks mentioned above can be managed by properly maintaining the diving suit, safety gear, and welding equipment.
Safety considerations
Underwater welding is hazardous work and hence following the safety precautions and procedures is very critical and important. Check and ensure that your underwater diving gear is in good shape since the failure of the gear in deep water can be hazardous and may lead to drowning.
- Maintain your diving suit and accessories in good shape and religiously inspect them every time before you wear them.
- Do not forget any of your diving accessories, including a diving knife and rubber hand gloves.
- It is a good practice to check the welding equipment by doing trial welding underwater before diving for the work. Do this every time.
- Have a clear understanding and communication method with the surface staff.
- You must be aware of your health limitations; taxing your body under deep water beyond your limit can lead to health issues connected to your lung, ear, and nose.
- Experienced underwater welders’ advice is that an underwater welder should never turn his back to the work when the DC current flows in the welding circuit. There are chances that the underwater welder may get entangled in the circuit. Always instruct your surface staff to ‘make it cold’ before you attend to any other issues.
- Using a DC generator is safe. Use straight polarity by connecting the negative terminal to the electrode holder and the positive terminal to work. Constantly update the welding equipment and keep the equipment in the best shape.
- Never use AC current for underwater welding. The electric shock induced by the AC current does not allow voluntary relaxation of the muscles that control the hand.
- Maintain the correct speed of welding, and never attempt to do it faster. Such acts can lead to disasters.
- The connection from the DC generator to the work and the electrode holder must have knife switches. The closing of these switches (to make the circuit operative) should happen only in the direction of the underwater welder. The means of communication should be very clear between the underwater welder and his onshore counterpart.
- The underwater welder should be aware of the dangers posed by deadly marine animals like sharks.
Application of underwater welding
The applications of underwater welding are very diverse, and they are listed below.
- There are underwater (submarine) pipelines laid for oil and gas transportation from one state to another state. Underwater welding is used during the laying of these pipelines and also for their repair and maintenance.
- Underwater welding is extensively used in dockyards to repair ships, submarines, and marine vessels.
- Underwater welding is used for the construction and maintenance of offshore drilling rigs and offshore platforms.
- Underwater nuclear power centers are an upcoming area where underwater welding is made use of.
- Underwater welding is also used during underwater mining.
In all the above cases, steel is the commonly used material.
References:
- Leisure pro – AquaViews – SCUBA Magazine.
- Wikipedia encyclopedia.
- Commercial Diving Academy.
- American Welding Society.
