Who signs it. A 3.1 certificate is issued by the manufacturer's authorised inspection representative, drawn from the actual heat. A 3.2 certificate additionally requires an inspector independent of the manufacturer, which means a third party is involved in or witnesses the testing.
The four inspection document types
EN 10204 defines four. A 2.1 is a declaration of compliance with the order, with no test results. A 2.2 is the same declaration plus results from non-specific inspection — that is, not from the material you are buying. A 3.1 carries specific test results from the actual heat, signed by the manufacturer's inspection department acting independently of production.
A 3.2 carries specific test results and is countersigned by an independent third party: an inspector appointed by the purchaser, or a notified body, depending on what the order says.
Why the difference costs money and time
A 3.1 is something we issue ourselves from data we generate. It is the normal document for industrial orders and it is what travels with most of the material we ship.
A 3.2 puts another organisation in the chain. The independent inspector has to be appointed, the test programme agreed, and attendance scheduled around the heat treatment and testing. That adds calendar time, and usually a charge, and it has to be known at the enquiry stage — it cannot be bolted on after the material is made.
What a buyer should check on the certificate
Heat number and its traceability to the physical bundle or bundle tag. The standard the material was made to. Chemistry against that standard's limits, not against a generic table. Mechanical results and the heat treatment condition they were obtained in. Non-destructive testing level and acceptance criteria. And, for pressure equipment, the notified body marking if the directive applies.
If your customer's specification names 3.2, a 3.1 will be rejected however good the material is. Say so at the enquiry, not at dispatch.