PMI · Advanced NDT
Positive Material Identification
The Method
How PMI works.
PMI measures the chemical composition of a metal and compares it with the specified grade. Two techniques are common in the field.
Handheld X-ray fluorescence (XRF) exposes the surface to X-rays and measures the characteristic X-rays each element emits in response. It is fast and leaves no mark, but it cannot measure carbon and has limited sensitivity to the lightest elements.
Optical emission spectroscopy (OES) uses an electrical spark to vaporize a tiny amount of surface material and analyzes the light it emits. OES can measure carbon — needed to tell low-carbon grades such as 304L from 304 — but leaves a small burn mark that may need cleanup.
Applications
Where PMI is used
- Alloy piping, fittings, flanges, and valves
- Weld deposits and filler metal
- Receiving inspection of incoming material
- Material verification programs for new and existing systems
- Sorting of mixed or unidentified stock
What PMI verifies
What PMI verifies
- Alloy grade against the specified material
- Major alloying elements such as chromium, nickel, molybdenum, manganese, and copper
- Carbon content, with OES
- Material mix-ups between similar-looking alloys
- Weld metal matching the specified filler
Methods & Equipment
Typical equipment
- Handheld X-ray fluorescence (XRF) analyzers
- Portable optical emission spectrometers (OES)
- Certified reference materials for verification checks
- Surface preparation tools
Technical Considerations
Limits and requirements to plan for.
Chemistry only
PMI confirms composition. It does not verify mechanical properties or heat treatment, and it does not detect flaws.
Carbon and light elements
XRF cannot measure carbon. When carbon matters, OES or another suitable technique is required.
Surface condition
Coatings, scale, and contamination affect results. The test area is prepared to clean metal.
Sampling plan
The specification sets how many items and locations are tested — 100% or a sampling plan.
In Practice
PMI in industry.
Shipbuilding & defense
Verification of alloy piping and components before installation.
Oil, gas & petrochemical
Material verification programs for alloy piping systems.
Fabrication shops
Receiving inspection and weld filler verification.
Industries that benefit
How TCI Supports You
What you get from TCI.
- PMI technicians experienced with XRF and OES techniques
- Results recorded against each item, heat number, or location
- PMI combined with receiving or source inspection
Let's discuss your inspection requirements.
Tell us about your project, schedule, and the specifications you work to. A member of our leadership team will respond directly.