Materials Verification · PMI
Positive Material Identification
Prove the alloy is what the certificate says it is.
Positive material identification (PMI) verifies the chemical composition and alloy grade of a metal component in situ, non-destructively — most commonly with handheld X-ray fluorescence (XRF). In seconds, the analyser reports the elements present and matches them to a grade, confirming that the installed material is what the specification and certificate claim.
The explainer
Watch how it works.
Schematic · loops automatically
1Prepare a clean spot
Coatings, scale and grime are locally removed — XRF reads the surface, so the surface must be the parent metal.
2Excite the atoms
The analyser’s X-ray beam ejects inner-shell electrons from atoms in the test spot.
3Elements fluoresce their fingerprints
Electrons falling into the vacancies emit X-rays at each element’s characteristic energies.
4The spectrum becomes chemistry
Peak energies identify the elements; peak sizes measure concentration — chromium, nickel, moly, all quantified.
5Grade confirmed — or flagged
The chemistry is matched to grade libraries: 316L confirmed, or the mismatch flagged before it enters service.
The physics
X-ray fluorescence works because every element’s atoms answer X-rays in their own voice. The analyser irradiates a small spot on the component; incoming X-rays eject inner-shell electrons from atoms in the surface, and as outer electrons drop into the vacancies, each element emits X-rays at its own characteristic energies — a fingerprint set by atomic physics, not by paint colour or paperwork.
The detector counts those characteristic photons and builds a spectrum: peaks at chromium, nickel, molybdenum, titanium energies, with heights proportional to concentration. Onboard libraries convert the measured chemistry into the nearest grade match — 316L versus 304, P11 versus carbon steel, Alloy 625 versus 825 — flagging any element outside the grade’s window.
PMI exists because material mix-ups are both easy and catastrophic: a carbon steel spool in a molybdenum-alloy service can corrode through in months, and the failure mode announces itself only in service. Verification programmes — in the spirit of API RP 578 — therefore test safety-critical components at receipt, at fabrication and in service, and PMI is the instrument that makes hundred-percent verification economically possible.
Where it earns its keep
Typical applications
- Verification of incoming alloy materials against certificates
- Weld consumable and completed-weld chemistry checks
- In-service confirmation on critical circuits (sour, high-temperature)
- Sorting mixed stock and investigating suspected substitutions
Standards & schemes
| Designation | Covers |
|---|---|
| API RP 578 (spirit) | Material verification programmes for new and existing alloy piping systems |
| Grade specifications | Chemistries assessed against the applicable ASTM/EN material standards |
PMI is delivered by trained operators under Metlab’s accredited quality system, with radiation-safety controls for XRF instruments and documented calibration and check standards.
Can PMI measure carbon content?
Routine handheld XRF cannot — carbon’s fluorescence is too weak. Where the decision hinges on carbon (L-grade stainless confirmation, carbon equivalents), portable optical emission spectroscopy or laboratory analysis is the correct tool, and we advise when the question demands it.
Is the X-ray from a PMI gun dangerous?
The beam is narrow, low-power and interlocked, and operators are trained in its controls; used as designed the technique is safe for operator and bystanders. It is still an X-ray device, so procedures and awareness apply — which is part of why PMI is an operator-trained method, not a toy.
When should a project specify 100% PMI?
Where the consequence of a material mix-up is intolerable: sour or lethal service, high-temperature hydrogen, critical alloy circuits in pharma and energy plant. For less critical systems, sampling regimes balance risk and cost — the verification programme defines it, and PMI executes it.
Testing · Inspection · Certification
Need PMI on your asset?
Describe the component, the material and the question — a specialist confirms the technique, the standard and the turnaround.