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Welding A Hot Topic Gets Hotter
Without advanced welding technology, modern shipbuilding would be impossible. But that does not mean maritime welding technology is free of quality issues and other challenges. Experts from Germanischer Lloyd explain.
The devil is always in the details. Welding is a complex and difficult process. Even the ISO 9000 standard for quality management systems refers to it as a "special process." No matter whether you are working on the outer hull, building a rudder or welding the hatch covers. While the result of welding is visible immediately, the quality of a weld is not so obvious. In fact, assessing it is quite a difficult task. "This is why it is so crucial to know exactly what you are doing," stresses Marcus von Busch, welding expert with Germanischer Lloyd.
Litmus Test
Before you can begin, the following questions should be clarified: "What kinds of materials am I going to weld, what kind of equipment and filler material will I need, and what will be the best method of joining the pieces?" Before beginning the actual assembly process, the selected combination should be tested. This welding procedure test, which is monitored and certified by technical experts from GL, scrutinizes the working processes that will be applied by the shipyard. Each individual welding task is simulated in a welding procedure test. The results serve as a basis for defining the specific procedure for joining each individual plate to the ship. The findings are documented in a Welding Procedure Specification that also indicates the settings for the welding unit, the consumables to be used, and how each welded seam should be prepared. In the Welding Procedure Test prior to each new project, Germanischer Lloyd examines whether the welders of the shipyard are capable of producing high-quality welds based on the existing welding instructions. During the test, a sample is welded up in the presence of a GL surveyor. The sample is then expedited to a GL-approved, accredited laboratory for non-destructive and destructive testing. These tests deliver solid data on the quality of the workmanship. They also reveal whether the steel properties (such as toughness and strength) that the designer used to determine the plates' dimensions will be preserved after welding. What complicates the matter is the fact that welding typically compromises the steel properties. For reasons of chemical composition, certain steel grades must be preheated prior to welding so they will cool down slowly after welding and maintain the desired properties. Cooling down too quickly will alter the internal structure of the steel: the steel will become harder and more brittle, both of which are undesirable characteristics in shipbuilding because they will make the steel more susceptible to cracking. "Our objective is to define a welding technique that will minimize the negative effects on the material properties," von Busch explains. "Of course, the best solution would be a ship without any welds at all. But unfortunately that is impossible," he smiles.
Eyes and Ears
PREPARATION. The quality of a weld is infl uenced by the way the seam is prepared.
(Photo Credit: Germanischer Lloyd January 2009 edition of NonStop)
have adequate equipment, qualified welding supervisors, welders certified for the required processes, and that their welding processes have been audited and approved. Aspects such as equipment, personnel and working procedures are audited by GL at regular intervals, usually every three years. In the event of a high churn rate of employees on a shipyard or a newbuilding project involving a new ship type, the tests may be performed more frequently. "For the on-site assessment of welding processes at the shipyards, our surveyors are our eyes and ears," says von Busch. "Back at headquarters we provide the welding technology expertise to our field surveyors and ensure we give them every bit of support they require. For every section of a ship we have a welding expert in-house to consult with � be it for building hulls, pipelines, pressure vessels or even engine crankcases or steam generators. We are planning to position welding experts in Asia, as well, so we can respond to customer requests even more quickly and directly," says von Busch.
Apart from this Welding-Procedure test, all companies carrying out welding work for GL-classed ships must have an operating permit issued by the classification society. To obtain the permit, they must prove that they
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