Codes, Standards & Specifications:
Underwater welding is covered under:
- AWS D3.6 Specification for Underwater Welding.
- ASME N-516 Underwater Welding Section XI Div. 1
- BS EN ISO 15618-1:2002 Qualification Testing of welders for underwater welding.
AWS D3.6M 1999 Specification for Underwater Welding:
- Class C – Where load bearing is not a primary consideration.
- Class O – To meet the requirements of another designated code or
Case N-516-3 Underwater Welding ASME Section XI:
Scope and General Requirement –
- Requirements for wet and dry underwater welding.
- Additional variables for dry underwater welding – Procedure and Performance qualification.
- Additional variables for wet underwater welding – Procedure and Performance qualification.
- Filler metal qualification – Each filler metal is tested in accordance with applicable SFA specification.
- Alternative procedure qualification requirements – By Charpy V-notch.
- Examination – By NDE.
Underwater inspection also includes visual and photographic examination of underwater structures and repairs, and NDE such as MT, UT, and RT.
Non-destructive Testing like UT, RT and MT can also be done underwater.
The photograph at figure 5 (Fig. 5) shows an underwater NDT technician using Magnetic Particle Testing on underwater structural supports.
Books are also available in the market for reference like;
- Non-destructive Examination of Underwater Welded Steel Structures.
- Underwater Wet Welding and Cutting.
- Underwater Repair Technology.
- Professional Diver’s Manual on wet Welding.
Visual, video and photographic examination can also be carried out during maintenance inspection on any underwater structures as shown below
In order to carry out a proper visual and NDT check, blast cleaning has to be carried out to remove all seawater organisms that grow on the underwater structure as shown on the photograph in Fig. 5.
Latest development in underwater inspection is the use of ROV’s. These are (Fig. 6) machines operated by an ROV pilot.
Below are some risks involved in underwater welding:
- Electric shock – there is a possibility of electric shock when the equipment is not properly insulated, or when the power supply is not shut off immediately when the welder terminates the arc during welding.
- Explosion – arc welding produces hydrogen and oxygen. Pockets of gasses can build up and are potentially explosive.
- Nitrogen Narcosis – a health hazard normally experienced by divers during the diving activities when safety stops at certain level is not adhered to. Curiously, the risk of drowning is not listed with the hazards of underwater welding.
- For welded structures, inspection of welds after welding maybe more difficult than welds made above water. There is a risk of defects that may remain undetected and may cause failure in the long run.
- OSHA Standard 1915.6 – Commercial Diving
- OSHA Standard 1910.424 – SCUBA Diving
- Volume IV, Issue 3, 3rd Quarter 2002
- Occupational Health Newsletter – Commercial
Safety during Welding:
- Necessary precautions should be carried out such as:
- Follow employers’ safety practices.
- Fumes and gasses can be hazardous to your health.
- Arc rays can injure eyes and skin.
- Use adequate ventilation while welding.
- Wear suitable eye protection and protective clothing.
- Do not touch live electrical parts.
- Wear rubber gloves.
- Only change the electrode when cold.
- With the latest development in construction of offshore oil platforms, there has been an increased demand for underwater welding. The use of hyperbaric chambers to produce code-quality weld is very expensive to operate.
- Sea Grant Researcher Dr. Chon Tsai, has developed a new welding electrode for wet welding nickname “Black Beauty” for the black appearance of its waterproof coating. The electrode exhibits excellent visual appearance and profile, micro-cracking of weld has been eliminated, operating characteristics are superior to other commercially available electrodes, and the electrode produces suitable results when used in any position.
Wet-Dry welding – Dry hyperbaric chambers or habitats are extremely expensive. This is because it must be built for special applications such as repairing or making tie-ins on horizontally laid pipes. Recent improvements allowed GMAW (Gas Metal Arc Welding) process to be used in underwater welding with the use of special nozzles, domes or miniature chambers. In using this type of apparatus the welder/diver is in the water but the nozzle of the welding gun and material to be welded is in the dry atmosphere. These localized dry gas environment chambers are inexpensive, small and lightweight. It is made of transparent material or has sufficient number of windows so that the welder can see the inside to properly manipulate and direct the welding gun. This process can be utilized for welding up to 125 ft. (35m) below the water surface.