1. Raw Material Defect Prevention
Strict control is implemented from the procurement and incoming inspection stages. Specific measures include:
Selecting compliant and qualified material suppliers, requiring them to provide complete material quality certification documents;
Upon arrival at the factory, conducting re-inspection and sampling according to standards to test composition and mechanical properties, and checking for surface defects such as cracks, scratches, and delamination;
Properly protecting materials during storage to avoid additional damage or corrosion during transportation and storage. 2. Welding Defect Prevention (The Most Core Control Link)
Welding is the process with the highest defect rate in pressure vessel manufacturing, requiring comprehensive control over materials, processes, and operations:
Material Control: Select qualified welding materials according to design requirements. Dry welding rods and fluxes as required before use. Thoroughly clean the bevel surface of oil, moisture, rust, and other impurities to control hydrogen sources.
Process Optimization: Select appropriate parameters through welding process qualification. Use low-hydrogen welding materials to reduce diffusible hydrogen content. For materials prone to cold cracking, such as high-strength steel, preheat before welding and perform hydrogen removal heat treatment after welding. Employ multi-layer welding to disperse restraint stress and avoid stress concentration.
Operation Control: Require welders to be certified and operate according to regulations. Thoroughly clean slag after each pass in multi-layer welding to avoid slag inclusions. Increase welding current to improve molten pool fluidity, promote slag and gas flotation, and reduce porosity and slag inclusion defects.
Post-Weld Inspection: After welding, use radiographic testing and ultrasonic testing to check for internal cracks, incomplete penetration, slag inclusions, and other defects. Remove any defects promptly and thoroughly before re-welding.
3. Geometric Dimension Deviation Control
To control dimensional deviations during forming and assembly, control measures include:
Machine machining bevels according to design requirements, ensuring bevel angles and edge straightness meet requirements; controlling uniform assembly gaps during assembly;
Selecting appropriate process parameters through welding process qualification to control welding deformation; after forming, strictly inspecting cylinder roundness, straightness, misalignment, and edge angles according to standards, adjusting promptly if deviations are found;
Controlling machining accuracy during plate rolling and head forming processes; after head forming, using templates to check shape deviations to avoid unevenness and exceeding tolerances.
4. Heat Treatment Defect Control
Setting accurate heat treatment process parameters based on material properties, strictly controlling temperature and speed;
Regarding residual stress after welding, ensuring that holding time and cooling rate meet specifications to ensure sufficient elimination of residual stress, avoiding incomplete annealing and residual stress, and preventing overheating that leads to coarse grains and reduced toughness.
5. Surface Defect Prevention and Control: Take protective measures during processing to avoid sharp mechanical damage caused by hoisting and machining; For localized scratches on the corrosion-resistant surface of stainless steel, repair grinding as required. If the grinding depth exceeds the standard, welding repair is necessary to prevent the defect from expanding under pressure.
