welding

Today on my work, a welder had to fix a crack in a casing from a gasturbine.The day before he already cut out the crack with a cutting torch.You have to remove the crack before you start welding,otherwise the crack continues after the welding repair.On the righthand side of the picture you see white blankets,underneeth them there are pre-heating elements installed.You have to pre-heat because the structure of metal changes when you heat it up during a welding process. You can change the hardness,ductility etc.Also the cooldown time is important hereby you can avoid cracks what can occurs when the metal cools down to fast.
Nice job welder!