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land of the crocodile 
After years of wear and tear, the lock gates at Cullen Bay Marina in Darwin, Australia, finally gave up the ghost. So local diving specialist Tim Proctor of Territory Diving was asked to take a look."We had a stroke of luck," said Tim. "I knew that David Keats, the underwater wet welding expert, was in the country opening a training centre. I was very much aware of David's reputation in the field. As the author of the UK's National Qualification and The Professional Divers Manual on Wet Welding, I knew he was the man for the job. I asked him to advise us on the suitability of wet welding". "One of the most difficult aspects of tackling any underwater welding job is to convince the client" said David, who is Managing Director of M.O.S. Speciality Welds in Shipley, UK. "Underwater wet welding generally has a very poor reputation, and the first thing I usually need to do is dispel the myths that surround this much-maligned process." After a number of meetings with the client where David provided evidence of the typical quality they could except from wet welding, they agreed that he should take a closer look at the gates. 
So, armed with all the details, he conducted an inspection dive. Then he submitted a proposal for a welding operation using his own Barracuda underwater electrodes and provided a method statement for their repair.The gates used a total of five hinge brackets, secured via a hinge pin, then welded to a steel channel in the side of the concrete lock wall. The first task was to remove the pins from each gate, to allow the gate to be removed from the lock. This involved the use of a number of heavy cranes. Then the task of removing the damaged hinges from the wall began. This involved divers cutting away the damaged weld using hydraulic grinders and air tools. Once all the hinges were removed, they were machined up ready for re-use. While this was taking place, Tim's divers were grinding out the old welds on the channel faces, ready for fitting the new hinges. Once all the hinges had been machined as required and the grinding was complete, the hinges were fitted to the gates, which were then lowered back into the water. With the help of local diver Noel Palmer, David guided each door so that all the hinges could be placed in position then tack welded into place. This was a somewhat delicate operation, as each door weighed more than 12 tons and each hinge weighed more than 70kg. "Any small movement on the top of the door, even of a few millimetres, would amount to a movement of many centimetres on the bottom, and even holding the door vertical had its problems," said David. "However, through the excellent team spirit of local contractor EC & E, controlling crane operations, and Territory Diving's surface support personnel, the task was accomplished in good time and without any serious hitches." For David, the biggest problems faced during the underwater work were the very poor visibility - and the imagined threat of crocodiles! "Being just a simple pom, the most dangerous thing I'd faced before was a discarded shopping trolley. But seriously, the water conditions in Darwin meant that visibility was usually extremely poor. In fact, fresh water was often pumped down to the diver in an attempt to improve matters." In the preparation of the hinge bracket, the bracket was cut back to aid overhead welding. In this way, the bubbles generated from the burning electrode could escape without interfering with the welding arc. The root and hot pass welding sequence was conducted in a series of 8 blocks to minimise stresses and distortion. 
Once these two passes had been put in, the welding followed a similar pattern, but attempts were made to ensure as few stop/starts as possible. The total number of passes was 9 for each bracket. This allowed for a 12mm leg length to be produced."Each hinge could take up to 4 hours to complete, and there were many hours of welding in total," said David. "Because Noel and myself were the only two qualified welders, spending up to 5 hours in the water at a time wasn't unusual. "It was a pleasure to work in Darwin with Tim's crew, EC & E, and of course the management of Cullen Bay. They all did a splendid job. "I am pleased to learn that, after 3 months back in use, the gates have performed without a hitch. This shows that, with proper procedures and control, wet welding can perform to realistic standards of quality and an attractive price." |
