It has long been considered that the most productive and cost effective welding position within the shipbuilding industry is the flat position (PA). To satisfy this, great emphasis is put in at the design stage to maximize the use of this position. However, even when adopting this philosophy, welding has to be carried out in a variety of other positions. Many shipyards have found major benefits when welding a specific section of the ship hull in the overhead position (PE).
Carbon steel to carbon steel link-ups
Large block sections of the ship are welded together in the block build strategy. On each section there are a large number of webs, girders and longitudinal connections to be made, in addition to the main hull connection. The bottom shell of the hull has traditionally been welded from the inside using a single V preparation, 60° inclusive angle with 6mm feather edge with flat ceramic tiles on the outside to produce a single sided weld. This weld requires no back gouging treatment, and for a time was considered to be the most effective way if completing the connection. However, there were disadvantages such as:
o Welder access,
o Obstructions from webs, girders, etc,
o Potentially higher defect levels on multi pass runs passing through access gaps
The alternative was to weld the connection from the outside, where minimum restrictions were available. This required reversing the preparation discussed earlier and welding the bottom shell of the ship in the overhead position. To achieve this, the following was carried out:
The joint was rooted from the inside against a round ceramic tile
Welding carried out from the outside using a Kat Oscillator and flux cored welding wire in the overhead (PE) position.
As the joint moves from the bottom shell it undergoes the transition from the overhead (PE) to the vertical (PG) position. The continuity of the weld is achieved by using the Kat welding carriage with oscillation head combination on flexible track. The weld is then continued up the side of the ship in the vertical position. When the technique was evaluated against the previous practice, man hours allocated to welding were decreased by 72%. When radiography test were done the results were consistently better than the previous welding procedure. In addition, the visual quality of the weld on both root and cap was of a very high standard. These benefits could not have been achieved without the following key elements:
A reliable oscillation system, and
A high integrity flux cored wire.
To date the Kat Oscillating System has been found to be extremely reliable in the variety of positions and environments within the shipbuilding industry. Two flux cored wires are being used, both are of Japanese origin, one is copper coated seamless wire and the other is a more traditional seamed wire. This practice has developed from extensive experience gained elsewhere in the shipyard on carbon and stainless steel. The results seen when using the Kat Oscillator welding carriage combination are a prime reason that shipyards throughout the world have been adopting new technologies to assist in the welding process.