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Description - Underwater welding can be divided into 3 main types:
Wet underwater welding: Among them, manual arc welding (MMA) is the most common process. In the former Soviet Union, flux cored arc welding (FCAW) has been widely used. Friction welding is relatively less sensitive to water depth and is suitable for robot operation and has certain potential for deep water maintenance.
Cofferdam welding: When in use, the submersible welder is placed in a hard steel structure to work in a dry gas phase environment.
High-pressure welding: used in sealed chambers near welded structures, which are filled with gas with a pressure slightly greater than the working water depth (usually helium with 0.5 bar of oxygen)
Current state
The most commonly used welding consumables are carbon-magnesium microalloyed steels for pipelines and offshore structures, as well as carbon-magnesium steels for ships and ports. The offshore platform was extensively repaired after being damaged by hurricanes or explosions. Although wet underwater welding is widely used, cofferdam welding is often used in port operations or ship repairs. In the former Soviet Union, semi-automatic flux cored arc welding (FCAW) was used to repair (shallow water) pipes and hulls underwater.
High-pressure welding using manual arc welding MMA (SMA), TIG (GTA) or flux cored arc welding (FCAW) is the preferred process for welding highly consistent welds, especially for deep water welding, including in the pipeline, oil and gas industries. About welding.
Current important issues
High pressure welding technology has been recognized and widely developed. However, when the water depth ranges from 500 to 1000 m, it is necessary to use a better technique in the development to complete the welding process.
Over the years, wet underwater arc welding (MMA/SMA) has been widely used to repair offshore platforms, including repairing offshore platforms that are subject to hurricanes or war damage. In the future, offshore structures made of high carbon equivalent steel will be repaired in deep water. Due to the wet underwater welding, hydrogen in the weld metal is largely diffused, and hydrogen induced cracking occurs as the carbon equivalent increases. This requires us to improve the electrode coating and improve the power technology.
If wet underwater cored arc welding (FCAW) can achieve a certain quality of welding, it may be more widely used.
benefit
Underwater welding provides a means of assembling and repairing underwater. This includes the use of fixtures and smears for repairs (which may cause unacceptably high loads on offshore structures), and flange repairs sometimes do not produce satisfactory results.
risk
Including human factors, there are three main types of risks. First, the potential risk is that welders or underwater workers may be exposed to electric shock. Precautions include the use of welding equipment with good insulation properties, immediate shutdown of the power supply, extinguishing of the arc, and limiting the no-load voltage of the manual arc welding (MMA/SMA) welding equipment. Second, the arc in wet welding and cutting produces hydrogen and oxygen, and measures must be taken to prevent the potential hazard of explosion due to gas accumulation. Another major risk is that when pressure increases, nitrogen exposed to the air can enter the blood circulation of welders or underwater workers with breathing, jeopardizing their health and safety. Precautionary measures include preparation of emergency air supply, alternate underwater workers and compression cabins to prevent staff from decompressing the disease after the diving has reached saturation and quickly rises back to the surface.
Post-weld inspection of welded components by wet-water welding may be more difficult than inspection of welds welded in air. In addition, it is difficult to ensure the consistency of the underwater welds, while there is still a risk that defects will not be discovered.
Professional technology
TWI's arc welding engineers and technicians have acquired a wealth of practical skills and experience through years of solving and developing industrial problems. Their consulting and research work includes: manual arc welding (MMA) consumables; flux core consumables and equipment; remote control, mechanized welding equipment; wet cutting technology.
Resources - equipment and consumables for wet welding; wet-welded tanks for preliminary testing; TWI Technology Center in Middlesbrough, northeast England, with indoor and deep-sea tanks and equipped with safe 24-hour equipment Provide advice on selecting welding processes, consumables, welds and best practices; troubleshooting and feasibility studies; and improving processes and equipment.
Underwater equipment
Located in Middlesbrough, in the northeast of England, the TWI Technology Center provides all support packages for professional researchers and operational needs in subsea and offshore operations. The latest equipment here meets the needs of subsea and offshore operators and meets the needs of personnel for underwater training, qualification, R&D, testing and improvement of equipment as well as inspection and calibration equipment.
In the UK, underwater tanks are the most modern underwater operations center. The tank has a diameter of 8m, a height of 6.5m and a volume of 318m3.
Underwater welding has been further developed at TWI: at Abington headquarters, TWI has a small wet-welded tank that can accommodate a welder or underwater crew; in Thailand, TWI also provides welders/ Training for underwater workers.
The Navy conducted underwater tests using TWI's underwater tanks. The underwater diagonal welding test designed by the Ministry of Defense to prove the feasibility of repairing the submarine has been successfully completed in the TWI diving tank.
Support for large maintenance teams
When BP completed difficult underwater repairs on a large platform at 182m deep water in the North Sea, staff from different technical departments at TWI would provide him with a wide range of maintenance technical support.
In-situ repair of the weld of the FPSO hull
A method suitable for repairing fatigue cracks in FPSO bottoms has been verified. Wet underwater welding welds the weld at the flat weld position, simulating the repair of fatigue cracks. The entire test process was very smooth and the repair was well repaired.
Development and trend of underwater welding technology
TWI has been conducting underwater welding research in ships, offshore operations and the oil and gas industry for more than 25 years. Its consulting and R&D work involves consumables, automated underwater welding and equipment.