1. Welding Defects (Highest Occurrence Rate, Most Prone to Defects)
Welding is one of the most critical processes in pressure vessel manufacturing, highly susceptible to human error, process parameters, and environmental factors, making it the most prone to defects. Common problems include porosity, slag inclusions, incomplete penetration, lack of fusion, undercut, and non-compliant weld dimensions. Welding cracks are the most dangerous type. These defects directly reduce weld strength and reliability, posing a major risk of leakage and rupture in pressure vessels later on.
2. Raw Material Defects
Raw materials themselves, or introduced during the incoming inspection stage, are prone to inherent or introduced defects such as cracks, inclusions, porosity, delamination, and surface scratches and pits. If inappropriate materials are selected or incoming inspection is not rigorous, these defects will be directly carried into the manufacturing process, affecting the overall strength and pressure resistance of the vessel.
3. Heat Treatment Defects
Heat treatment is a crucial process for eliminating residual welding stress and adjusting material toughness. Defects are easily generated due to improper control of process parameters. Common problems include insufficient annealing, resulting in unresolved residual stress and insufficient material toughness, as well as overheating and cracking, increasing the risk of brittle fracture of the vessel.
4. Geometric Dimensional Deviations: These defects are prone to occur during the forming and processing stage. Common examples include excessive ellipticity of the cylinder, excessive misalignment of weld joints, unevenness of the end caps, and excessive verticality of upright vessels. Excessive ellipticity of the cylinder is a particularly common problem, leading to installation difficulties or localized stress concentration, thus affecting structural safety.
5. Cold Working Defects: Cold working processes (such as plate rolling and straightening) are prone to residual stress and warping. Even if the residual internal stress does not directly cause cracks, it can exacerbate fatigue fracture and stress corrosion cracking in pressure vessels later on.
