A team of Hydrex diving/welding technicians was recently mobilized to Dakar, where a 225m drill ship needed urgent repair. The vessel’s transit flap had become loose and started swinging dangerously. This had caused damage to the aft bulkhead and a leak in a ballast tank, situated aft of the moonpool.
Following an inspection, the divers removed the transit flap – the flap being in unstable condition meant that this operation had to be carried out to the highest safety standards – and took measurements of the damaged areas. This allowed a total of six doubler plates to be fabricated onshore. These plates were then positioned and secured by the team of underwater welders. With the damaged ballast tank emptied of all water, the tank was inspected and found to be fully sealed. This allowed the ship to safely start its contract; a permanent repair can be planned for a more convenient time.
Disconnected transit flap brought to shore during operation in Dakar
Hydrex Production Executive Dave Bleyenberg points out that underwater welding is a highly specialised procedure. “One of the largest hurdles to successful wet welds lies in the sporadic outflow of gas bubbles from the point of contact with the arc and metal,” he explains. “This reaction causes major porosity in the welds, as the bubbles burst out, uncontrolled.”
Bleyenberg briefly explains the history of the techniques developed to deal with the problem. “Russian engineer Konstantin Khrenov was the first, in 1932, to devise a waterproof coating for the electrodes and a stable power source. But it was not until the 1970s that underwater welding was first qualified by AWS standards and commercialised by White Grubbs and Dale Anders of Chicago Bridge and Iron.”
“Hydrex was quick to adopt the new wet welding technology and has now been at the forefront of underwater welding for well over 40 years,” continues Bleyenberg. “During that time, our in-house R&D department has further refined the procedures and has developed new equipment that makes it much easier to monitor and test the weld seams. The R&D and diving teams work closely together to keep evolving new welding techniques.”
Training is a vital part of the equation, with Hydrex offering in-house theoretical courses and practical training in the company’s three dive tanks. “Learning continues as new divers get the opportunity to assist veteran team members during real operations,” adds Bleyenberg.
Other jobs completed by Hydrex include repairing cracks along the rudder flap hinges on a 228m vehicle carrier. The smaller cracks could be repaired by grinding and filling the area with clad welding, but three larger cracks required C-shaped plates to be manufactured, then secured over the cracks by wet welding in position.
Although Hydrex recommends regular underwater inspections so that problems can be identified early, this cannot always happen. Two thruster brackets on a 278m container ships were found to be in a very advanced state of cracking. Hydrex, working with the class surveyor, was able to install four steel plates under water, thus preventing an unscheduled drydocking and allowing the ship to sail until a more permanent repair could be arranged.
Using it patented Mobdock concept (mobile mini drydock), Hydrex diver/technicians can perform permanent repairs to all parts of the underwater ship propulsion system, as well as steel work or crack repairs in drydock-like conditions.
Because of the nature of repair work, it is often necessary for solutions to difficult problems to be worked out in a short time period, sometimes even after an operation has already started. Through a worldwide network of offices and service stations, Hydrex can provide start-to-finish solutions economically at any location.