When Is PMI Testing Needed?

PMI measures the alloy composition of a part with a portable spectrometer. The result comes in seconds and shows whether the material really is the grade stated.

What it is for

A certificate tells you which melt the part came from; PMI measures the composition of the part in your hand. They answer different questions. Cases where the certificate is correct but the parts got mixed are not rare: F304 and F316 look identical, and P11 cannot be told from P22 by eye.

When it is needed

• On alloy and stainless items. F304/F316, F11/F22/F91 and duplex grades cannot be distinguished visually.
• In sour and corrosive service. A wrong grade is a direct safety issue.
• Where stock mixing is a risk. When different grades share a rack.
• When the specification requires it. A frequent condition on refinery and petrochemical projects.

When it is not needed

PMI does not discriminate between carbon steel grades; the difference between A105 and A350 LF2 comes from impact testing rather than composition. There, the mechanical values and heat treatment record on the certificate matter more.

Its limits

• It cannot measure carbon reliably, so it is unsuitable for carbon equivalent checks
• A dirty, painted or rusty surface distorts the result; the test spot must be cleaned
• Weld metal and parent metal must be measured separately
• It shows nothing about mechanical properties or heat treatment

Cost and schedule

PMI is charged per part and adds a step before shipment. On critical items that cost is nothing next to finding the wrong material on site. Stating the requirement at enquiry stage keeps both price and lead time accurate.

We add PMI reports to the shipping file for alloy items. Send your list through the enquiry form, and see how to read a mill test report for the certificate side.

FAQ

Does PMI replace the certificate?
No. PMI measures composition, while mechanical values, heat treatment and traceability come from the certificate.

Is PMI useful on carbon steel?
Only to a limited extent, because it cannot measure carbon reliably enough to separate carbon steel grades.

Does PMI damage the part?
No, it is non destructive. Only the test spot needs cleaning of paint and rust.