The 3.1 certificate is signed by an authorized inspection representative of the manufacturer and must be consistent with the order, grade and standard.

Key fields: - Heat No.: must be traceable to the melting records and consistent across the same batch of material. - Chemical composition: check whether C, Cr, Ni and Mo are within the standard ranges. - Mechanical properties: yield strength, tensile strength and elongation; note the sampling direction and heat-treatment condition. - Heat-treatment condition: solution treatment, annealing or hard condition, which directly affects processability. - Standard declaration and signature: standard number, version, issuer and date must all be present.

Common risks: certificate heat number not matching the actual material, blank mechanical-property fields, and passing off a 2.2 certificate as a 3.1.