Positive Material Identification: XRF and OES Alloy Verification

Positive material identification confirms that the alloy in front of you is the alloy that the specification called for. Material substitution happens, through mislabelling, mixed stock, lost documentation or deliberate supply of a cheaper grade, and the consequence appears in service as accelerated corrosion, cracking or failure under conditions that the correct material would have withstood. itmad provides PMI and alloy verification by XRF and optical emission spectrometry (OES) to ASTM E1476, ASTM E572 and API 578, on site, in fabrication yards and offshore. itmad operates across the Middle East, Asia and Europe. Last reviewed: October 2026.

Methods

X-ray fluorescence (XRF) is handheld, entirely non-destructive and fast enough to check a full population of components and not just a sample. It identifies alloying elements and matches the result against a grade library to ASTM E572 and ASTM E1476, and suits verification, sorting and screening in the field. Optical emission spectrometry (OES) vaporises a small area of the surface with an electrical arc and analyses the emitted light. It is slower and leaves a small burn mark, but it measures elements that XRF cannot, including carbon, sulphur and phosphorus, and gives full quantitative composition to ASTM E415 and ASTM E1251 and not identification alone.

Why carbon decides the method

XRF cannot measure carbon. It is a light element and produces no usable fluorescence signal, so an XRF instrument cannot distinguish 304 from 304L, or 316 from 316L, because those grades differ almost entirely in carbon content. The alloying elements read identically and the instrument reports a match.

This matters because L grades exist specifically to resist sensitisation and intergranular corrosion after welding. A component supplied as 316 where 316L was specified will pass an XRF check and fail in service. Where the specification distinguishes an L grade, or sets limits on carbon, sulphur, phosphorus or boron, OES is required, and itmad says so and does not issue an XRF result that appears to confirm compliance it cannot establish.

Elements and alloys

OES with a UV probe measures carbon, phosphorus, sulphur, tin, arsenic and boron in steels, and aluminium, magnesium and silicon in aluminium alloys, in situ. itmad routinely analyses ferrous alloys, including carbon and low alloy steels, stainless and duplex grades, nickel alloys, aluminium alloys and copper-based alloys, and reports the full composition against the material specification.

Where PMI is required

PMI is used for incoming material verification where certification is missing, incomplete or in doubt; verification of welding consumables and completed weld deposits; confirmation that installed components match the piping or equipment specification; alloy sorting where stock has been mixed or identification lost; and verification after maintenance, where the origin of a replacement part is unknown. It is also used in refinery and petrochemical PMI programmes covering pressure-retaining components to API 578, in failure investigation to establish whether material substitution contributed, and for pre-shipment verification of fabricated assemblies.

Standards applied

ASTM E1476 covers metals identification, grade verification and rating, ASTM E572 the analysis of stainless and alloy steels by XRF, ASTM E415 the analysis of carbon and low alloy steel by OES and ASTM E1251 the analysis of aluminium and aluminium alloys by OES. API 578 covers material verification programmes for new and existing alloy piping systems, and client and project specifications, including operator PMI procedures, apply where they govern.

Surface preparation

Both methods read the surface, so a result is only as good as what the instrument sees. Coatings, scale, oxide, weld spatter and surface contamination must be removed to clean base metal before analysis, and grinding residue from a wheel used on another material will itself skew the result. Preparation is part of the procedure and not a preliminary to it.

Where the work is done

PMI is carried out on site, in fabrication yards, at refineries and offshore, or on components submitted to itmad, with portable instruments that need no power supply at the test location. Analysis is performed by technicians and chemists experienced in alloy verification.

What the client receives

A report that identifies each component tested by line number, weld number or part reference, with the method and instrument used and calibration verification against certified reference materials. It gives the measured composition element by element and the grade identified, and confirms match or mismatch against the specification. It states explicitly where carbon was not measured and what that means for the conclusion, and components are marked on site where the client's procedure requires it.

Frequently asked questions

What is positive material identification (PMI)?

It confirms that the alloy in a component or structure is the alloy that the specification called for, by XRF or optical emission spectrometry, with results reported element by element against the specification. It is applied to ASTM E1476, ASTM E572 and API 578.

What is the difference between XRF and OES?

XRF is handheld, entirely non-destructive and fast enough to check a full population, and it matches alloying elements to a grade library. OES vaporises a small area with an arc and measures elements XRF cannot, particularly carbon, sulphur and phosphorus.

Why can XRF not tell 316 from 316L?

XRF cannot measure carbon, and those grades differ almost entirely in carbon content. A component supplied as 316 where 316L was specified will pass an XRF check and fail in service, so OES is required where an L grade is specified.

Which standards apply?

ASTM E1476, ASTM E572, ASTM E415 and ASTM E1251, and API 578 for alloy piping verification programmes. Client and operator PMI procedures are applied where they govern.

When is PMI required?

For incoming material with missing certification, welding consumables and weld deposits, installed components, mixed stock and replacement parts of unknown origin. It is also used in API 578 programmes, in failure investigation and for pre-shipment verification.

What does a PMI report state?

The component identification, the method and calibration verification, the measured composition element by element, and a match or mismatch against the specification. It states explicitly where carbon was not measured and what that means for the conclusion.