Precautions for the welding process of ship steel plate

1. Control of welding line energy

The DNV GL grade B ship steel plate should be welded strictly in accordance with the process specification, and the welding heat input is generally controlled below 5000J/cm. If the heat input is too large, the weld metal will stay at a high temperature for a long time, which will cause the heat-affected zone to overheat and make the grains coarse, make the structure plasticity worse, and reduce the crack resistance of the joint; while the heat input is too small, it will cool the joint The speed is increased, the cooling time is shortened, and the heat-affected zone is hardened, which is also not conducive to the escape of hydrogen, so it also increases the tendency of cold cracking. Therefore, the welding heat input should be strictly controlled during construction.

2. Operational control

The welding environment of ship plates should be stable to avoid air flow affecting the gas protection effect. Try to avoid welding in a humid environment. Because of the multi-pass welding, the splash cleaning between layers must be thorough. Before welding on the back, use gouging to thoroughly clean the roots, grind the grooves, and clean them before welding.

Post-welding inspection and treatment

1. Visual inspection

The surface of the weld should be flat and smooth, the width of the weld should be the same, and the extra height should meet the process requirements. The surface of the ship plate is to be free of defects such as pores, cracks, undercuts, etc.

2. Non-destructive testing

Use magnetic powder to inspect the weld surface and near-surface defects. Then use ultrasonic to inspect the weld. Subsequently, the welds were inspected by X-ray filming.

3. Defect treatment

If pores, cracks and other excessive defects such as slag inclusions, undercuts, lack of fusion, etc. are found during the inspection of the ship steel plate, the defective parts shall be batch removed. The batch should be polished and cleaned before welding.