PMI (Positive Material Identification) verified that alloy materials are of acceptable chemical composition independent of any certificate and marking that may exist.
API RP 578 is an excellent document for instituting an effective PMI program. MSS SP-137 is also another useful standard.
As a result of PMI test, alloying elements shall be within the range specified by the applicable material standard by taking into account also the accuracy of the instrument (i.e. instrumental error).
For guidelines on test equipment or methods used for testing, a written specification should be consulted.
The above Table is an example and may be changed based on project requirements.
