Corrosion

Corrosion is the destruction of metal through reaction with its environment — classically the rusting of iron through oxygen and water. There are many types: uniform attack, pitting, stress-corrosion cracking, intergranular corrosion, crevice and galvanic corrosion. Each has its own causes and countermeasures. For welders the key point: the weld is often the weakest spot, because the microstructure is altered there and heat tints weaken the passive layer.