Underwater welding process

Underwater welding

Underwater welding process

Underwater welding is a process of welding at elevated pressure, normally underwater. Underwater welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure and hence a dry environment. It is predominantly referred to as "hyperbaric welding" when used in a dry environment and "underwater welding" when in a wet environment.

There are two types of underwater welding. They are as follows:

1. Dry 

2. Wet

DRY WELDING

> Dry underwater welding involves the weld being performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded.

> Most welding process SMAW, FCAW, DTAW, GMAW, PAW could be operated at hyperbaric pressure but all suffer as the pressure increase. Gas tungsten arc welding is most commonly used.

> A large number of techniques are available for welding in atmosphere, many of these techniques can not be applied in offshore and marine application where the pressure of water is of major concern.

> In this regard, it is relevant to take note that, a great majority of offshore repairing and surfacing work is carried out at a relatively shallow depth, in the region intermittently covered by the water known as the splash zone.

> Though, numerically most  ship repair and welding jobs are carried out at a shallow water depth, most technologically challenging tasks lies in the repairing at a deeper water level, especially, in pipelines and occurrence of sudden defects leading to a catastrophic accidental failure.

> Thats why dry welding techniques have been applied which have allowed welding down to 2500m simulated water water depth in laboratory, but it ha thus far been limited operationally to less than 4oom water depth by the physiological capacity of divers to oerate the welding equipment at high pressure.

ADVANTAGES

1. Save the valuable time and dry docking cost

2. Welder/Diver safe from marine animals and bad weather

3. This method has ability to produce weld of quality comparable than wet welding

4. Join preparation, pipe alignment, NDT inspection etc are monitored visually

DISADVNTAGES

1. Cost of habitat welding is extremely high and increase with depth

2. At greater depth the arc constricts and corresponding higher voltages are required

3. Using a lot of complex and costly equipment

WET WELDING

> Its involves using special rod and is similar ti the process in ordinary air welding. The work to be welded is connecting with electric circuit and a metal electrode to the other side.

> These two parts of the circuit are bought together and then separated slightly. The electric circuit jumps the gap and cause a sustained spark(arc), which melts the bare metal, forming a weld pool.

> At the same time , the top of electrode melts and metal droplets are projected into the weld pool. During this process the flux covering the electrode melts to provide a shielding gas which is used to stabilize the arc column and shield the transfer metal.

> The arc burns in a cavity formed inside the flux covering which is designed to burn slower than the metal barrel of the electrode

> For underwater welding special type of ilmenite coating is applied around the electrodes.

ADVANTAGES

1. It is less costly than Dry welding

2. This process is most time and cost saving method highly desirable

3. Any part of the structure diver can reach and weld

4. No enclosure needed 

5. Equipment available in work place

DISADVANTAGES

1. Poor visibility in water

2. Diver unsafe from bad weather and marine animals

3. Higher energy density of hydrogen, higher efficiency

4. Rapid quenching decrease impact strength and ductility

SAFETY MEASURES

> Areas and voids must be vented or made inert

> Precautions include achieving adequate electrical insulation of the welding equipment

> Maintain highest caution topside and underwater

> Prepare proper HIRA to eliminate the risk 

> Maintain proper communication with diver and top side

Note: Hope my hard works helping you to understand the Underwater welding procedure. Hoping for the best

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