A Hot Topic Gets Hotter

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.

Litmus Test
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, GL 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
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 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. "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. 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.

Material Under Test
What steel grades will be processed? What are their properties? And what would be the best filler material for the given steel grade? These questions must likewise be addressed before embarking on a new welding project. The GL welding experts will work together closely with their colleagues from the material technology department. This cooperation ensures optimal, high-quality results - after all, each steel plate and each filler material to be used for a given GL ship is tested and certified by the classification society. As part of this process, manufacturers of filler materials must prove once a year that the quality of their wires and electrodes continues to fulfil the GL requirements.

To define quality standards for welding, GL has issued procedural guidelines within the framework of its technical rules. These guidelines explain how to avoid mistakes and flaws in welding, providing answers to questions such as: What should be the temperature of specific steel grades prior to welding? How should the welded seam be tested upon completion? Is it permissible to make any welds at all in high-stress areas of a ship, such as hatch corners or free edges? According to the GL rules, welding should generally be avoided in high-stress areas. Welding technology is evolving at a breathtaking pace. New welding processes, materials and methods are emerging constantly. No matter what factors may influence or even perhaps revolutionize welding technology in the years to come, GL will be at the forefront of the research and development effort.