Metal welding creates stresses in the material surrounding the weld. An undesired situation, as this may cause cracks or tears in the steel. Preheating the components to be welded ensures that welding stresses are kept to a minimum.
Preheating is used to bring the material to be welded to a certain base temperature of between 100 and 200 degrees Celsius. This process reduces the temperature difference between the weld and the material to be welded, which in turn reduces thermal stresses. Preheating the welding work also reduces the cooling rate after welding, Which prevents the occurrence of undesired hardening. By preventing hard zones, the risk of so-called cold cracking is minimised. This is because the hydrogen present – the cause of the cracking – is given more time to disappear from the material when preheated. Furthermore, reducing the cooling rate prevents a lack of fusion. A cooling period that is too short means the material retains too little heat to smelt the bevels together.
Preheating is frequently applied to welding work to pipes, such as in the offshore sector, (petro)chemicals and in the shipping industry. The preheating of welding always occurs on site and is carried out in close collaboration with the client’s welders. After all, as soon as the material has reached the right temperature through preheating, the welding has to take place immediately. Preheating of -for example – pipes on site is done by way of resistance heating or induction heating.
Weld preheating improves the durability of the material, so that less maintenance is required and the material has a longer service life. This heat treatment is mainly applied to materials with a thickness of more than 10 millimetres. Depending on the type of material, its thickness and particularly your wishes as our client, an additional second heat treatment after welding is complete can be applied on top of the preheating process: stress relieving annealing of the material.