API 572 RP – Inspection of Pressure Vessels Practice Test

Most cracks in pressure vessels typically occur at welds and in heat-affected zones due to the stress concentrations and metallurgical changes that happen during the welding process. When two pieces of metal are joined together, the intense heat can alter the microstructure of the material in the vicinity of the weld. This can lead to a reduction in toughness and increased susceptibility to cracking, particularly under stress or in the presence of corrosive environments.

Additionally, welds are often subject to different thermal cycles than the base metal, which can create residual stresses. These residual stresses, combined with the notches created at the weld interface, can significantly increase the likelihood of crack formation. As vessels are subjected to internal pressure and operational stresses, these areas become critical points where failures are more likely to initiate and propagate.

While cracks can occur in other areas of the vessel, such as the body, near the nozzles, or on the surface, the combination of stresses and material changes at the welds and heat-affected zones makes them the most common locations for crack initiation.