How to Weld Underwater

Underwater welding is a process whereby metals are melted together underwater to either repair a structure or create a new structure. Used on oil wells, ships, and other underwater structures, underwater welding is done by one of two methods. The first is hyperbaric welding, in which a structure is created around the weld and a pressurized environment created. The second is arc welding, in which the welding electrode contains a flux coating that releases gases to preserve the integrity of the weld. Because of the dangers of shock, explosion and poisoning, underwater welding is only performed by professionals with both diving and welding certifications.

Method 1 of 2: Hyperbaric welding

1. Identify the site and material of the joint to be welded as most underwater welds involve steel, but metals may vary.
2. Prepare a chamber to place around the joint (each joint should have a separate chamber).
3. Introduce gas into the chamber. A typical gas mixture uses helium and oxygen, but requirements vary based on the specific joint to be welded. The pressure of the chamber should be slightly above that of the surrounding water.
4. Run a power supply to the chamber and set up a port for your electrodes. Multiple electrodes will likely be required, and should be placed in advance in front of the area of the joint to be welded.
5. Dive to the weld site.
6. Turn on the power supply and weld the joint from outside the chamber
7. Turn off the power supply as soon as the welding is done.

Method 2 of 2: Arc welding

1. Investigate the joint to be welded and identify the types of metals involved.
2. Prepare the adequate electrodes, plan out the order of welding and dive to the weld site.
3. Weld the joint, ensuring that the flux coating of the weld is coming off as expected, and that too much hydrogen is not approaching the joint.
4. Turn off the power supply as soon as the welding is done.

In addition to underwater hyperbaric welding and underwater arc welding, a common way of welding joints on surfaces underwater is to bring the surface onto dry land, create a pressurized chamber around the joint, and use a hyperbaric dry welding process. This eliminates the need for diving while still reaching normally underwater locations.

WARNINGS

• Explosions can occur when pockets of hydrogen or oxygen build up and are exposed to a flame. Ensure that there is a method for venting built-up hydrogen and oxygen, and review all safety procedures beforehand.
• Because underwater welding involves two dangerous activities–welding and diving–years of instruction are usually needed before attaining competence. When learning how to weld underwater, do not attempt it if you are only comfortable as a welder or as a diver.
• Underwater welding is only done with special electrodes designed for prolonged contact with water. Check that all electrodes and power supplies are adequately insulated.
• Poisoning from nitrogen or other gases can cause permanent injury or death while welding underwater. Divers should always have an external or back-up air supply and should use a depressurizing chamber when returning to the surface.

Source :

http://www.wikihow.com/Weld-Underwater