What are some common manufacturing defects in pressure vessels?

I. Welding Defects (Most Common and Critical)
Welding is the core process in pressure vessel manufacturing and a high-risk area for defects, mainly including:

1. Incomplete Penetration and Lack of Fusion: Incomplete melting at the weld root or insufficient bonding between the weld bead and the base metal weakens the connection strength.

2. Slag Inclusions and Porosity: Residual slag or gas trapped in the weld during welding creates stress concentration points.

3. Cracks: Including hot cracks, cold cracks, and reheat cracks, these are among the most dangerous defects, easily leading to brittle fracture.

4. Surface Defects: Such as undercut (arc-damaged base metal at the weld edge), weld beads (excess metal accumulation), and craters (depressions at the end of the arc), which easily trigger fatigue cracks.

5. Incorrect Weld Dimensions: Such as excessive height, excessive narrowness, or uneven transitions, affecting the uniformity of structural stress.

II. Materials and Internal Defects

1. Delamination and Inclusions: Non-metallic inclusions or lamellar tears within the steel plate disrupt material continuity and reduce load-bearing capacity.

2. Inappropriate Material Selection: Using materials that do not meet design requirements or have substandard chemical composition affects pressure resistance and corrosion resistance.

III. Forming and Assembly Defects

1. Surface Mechanical Damage: Defects such as pits, scratches, and dents can become crack initiations under pressure.

2. Bulging and Deformation: Problems with the mold or improper operation during forming can cause localized bulges or non-circular cross-sections, leading to stress concentration.

3. Misalignment and Sharp Edges: Misalignment of the steel plates on both sides of the butt weld creates a stepped misalignment, affecting weld quality and exacerbating localized stress.

4. Wrinkles and Excessive Thinning: Wrinkles or excessive wall thinning during head pressing reduce pressure resistance.

IV. Other Manufacturing-Related Defects

1. Improper Heat Treatment: Insufficient annealing can lead to unresolved residual stress, increasing the risk of brittle fracture.

2. Inspection Omissions: Inadequate non-destructive testing covering critical areas or lax adherence to rejection criteria can allow potential problems to persist into the service life.