3.1 vs 3.2
A 3.1 MTC is signed by the mill's independent QA. A 3.2 adds counter-validation by an authorized third-party inspector (TUV, BV, LR) — typically required for PED, IBR and offshore work.
What to Cross-Check
Heat number must match the material stamping; chemistry must satisfy the spec, not just the brochure; mechanicals must report yield, UTS and elongation per orientation.
Beyond Paper
Demand PMI (Positive Material Identification) on receipt for any high-nickel alloy, and randomly request hardness checks for sour-service materials per NACE MR0175.
