Key Considerations
1. Standard Requirements (GB/T 4171-2008)
Mill Test Certificate (MTC) is mandatory:
The steel mill must provide an MTC (also called a "quality certificate") including:
Chemical composition (C, Si, Mn, P, S, Cu, Cr, Ni, etc.).
Mechanical properties (tensile/yield strength, elongation, impact toughness at -40°C).
The MTC serves as the primary proof of compliance.
Third-party inspection is optional:
GB/T 4171 does not require independent verification unless specified in the purchase contract.
2. When Is a Third-Party Report Needed?
High-risk applications: Bridges, offshore structures, or seismic zones.
International projects: Buyers (e.g., in Europe, the Middle East) often demand SGS, BV, or Lloyd's reports.
Dispute prevention: If the buyer distrusts the mill's self-certification.
3. What Does Third-Party Inspection Cover?
Typical checks by agencies like SGS, BV, or CCIC:
Material verification: Confirm MTC data matches delivered batches.
Retesting: Random sampling for:
Chemical analysis (OES spectrometer).
Mechanical tests (tensile, impact, bending).
Visual/dimensional inspection: Thickness, surface defects.
4. Risks of Skipping Third-Party Inspection
Fraud risk: Some mills may falsify MTCs (e.g., selling Q355NH as Q460NH).
Hidden defects: Poor toughness, incorrect alloy ratios.
Project delays: Failed material discovered during construction.
Best Practices
| Scenario | Recommended Action |
|---|---|
| Domestic project, trusted mill | Mill's MTC is sufficient. |
| Export/overseas buyer | Require third-party inspection (e.g., SGS). |
| Critical structure (bridge, high-rise) | Mill MTC + third-party retesting. |
| Unverified supplier | Mandate third-party inspection before payment. |
