I. Why Cracked Steel Pipes Must Not Be Used?
1. Cracks Will Continue to Propagate: Under pressure, vibration, or temperature changes, stress concentration occurs at the crack tip, causing rapid propagation and ultimately leading to sudden fracture.
2. Significantly Reduced Load-Bearing Capacity: Even seemingly small cracks can reduce the steel pipe's load-bearing capacity to below 30% of the design value, far below safety standards.
3. Irreversible Structural Damage: Cracks represent damage to the material itself and cannot be restored to their original strength and sealing performance through simple repairs.
⚠️ Special Reminder: According to the "Safety Technical Specification for Construction Scaffolding with Couplers" JGJ130, any steel pipe with a transverse or longitudinal crack depth > 0.8mm should be scrapped.
II. Correct Handling Procedures After Discovering a Crack
1. Immediate Stoppage and Isolation: Cut off the flow of the medium (e.g., water, gas, oil), depressurize, and isolate the cracked pipe section to prevent the accident from escalating.
2. Professional Inspection and Status Confirmation
Magnetic particle inspection (MT) is used to detect surface and near-surface cracks;
Ultrasonic testing (UT) is used to determine if cracks penetrate the pipe and have internal extension;
It is recommended to use a combination of MT and UT for comprehensive evaluation.
3. Decision Based on Inspection Results
Mandatory Replacement: Cracks penetrate the pipe wall, are longer than 50mm, or are located in high-stress areas such as elbows/welds;
Temporary Emergency Repair (Limited to Low-Pressure Non-Critical Systems): Reinforce with metal repair adhesive or mechanical sleeves, but replacement is required as soon as possible;
Rework Permitted: Limited to shallow hairline cracks; after grinding, re-inspection is required to confirm the absence of residual defects.
III. How to Prevent Recurrence of Similar Problems?
1. Source Control: Use high-purity billets, controlling inclusion levels to ≤2;
2. Process Optimization: Ensure uniform heating and matching rolling parameters to avoid stress concentration;
3. Heat Treatment Specifications: Complete tempering within 2 hours after quenching to prevent delayed cracking;
4. Closed-Loop Factory Inspection: Each steel pipe must pass a triple inspection including hydrostatic testing, UT, and MT.
✅ Recommendation: In critical scenarios such as high-pressure boilers and oil and gas transportation, prioritize products from manufacturers with API 5CT and GB 5310 certifications to ensure process compliance.
