Which defects have the greatest impact on pressure vessel safety?

1. Corrosion Defects: Intergranular Corrosion is the most dangerous. Intergranular corrosion occurs along the boundaries of metal grains, directly destroying the bonding force between grains and causing a sharp decline in the material's mechanical properties. Moreover, the corrosion location is hidden, and the vessel's appearance usually does not show obvious changes. However, under high pressure, it can suddenly cause brittle fracture, which is difficult to predict and prevent. Its danger is far greater than uniform corrosion and pitting corrosion. Uniform corrosion can be protected by pre-existing wall thickness and is easy to monitor. Pitting corrosion is localized and easy to detect, and its risk is lower than intergranular corrosion.

2. Manufacturing/Welding Defects: Welding Cracks are the most dangerous. Welding cracks are the sharpest notch defects. The radius of curvature at the notch root is close to zero, causing extremely severe stress concentration. It is a major cause of brittle fracture, fatigue fracture, and stress corrosion cracking in pressure vessels. Furthermore, cracks easily continue to propagate, potentially leading to sudden vessel failure. It is the most dangerous type of welding defect, far exceeding other welding defects such as porosity, slag inclusions, and excessive misalignment.

In addition to the two types of high-risk defects mentioned above, three other types of manufacturing defects can significantly impact safety:

Geometric discontinuities: Such as misaligned joints, angular deformation, non-circular cross-sections of the cylinder, and unevenness of the end caps, these defects can induce additional bending stress, causing excessively high local stress. For vessels under external pressure, non-circular cross-sections may also lower the critical pressure, ultimately leading to instability and collapse.

Residual internal stress: Internal stress remaining after welding and cold working, even if it does not directly cause cracks, can exacerbate fatigue fracture and stress corrosion cracking in pressure vessels, and is a major cause of stress corrosion cracking.

Incomplete penetration: This creates obvious gaps inside the weld, resulting in severe stress concentration, and is also a common cause of brittle fracture and fatigue fracture.