# Positive material identification

Selecting and interpreting XRF, OES, and LIBS checks of alloy composition without confusing a grade match with full material conformance.

Reviewed: 2026-11-01

Tags: inspection, material-verification, spectroscopy

Positive material identification (PMI) checks selected elements against the intended material. Petroleum Development Oman’s SP-2472, version 0 (June 2024), supplements API RP 578 fourth edition (February 2023) with owner-specific rules. [PDO SP-2472, scope and program requirements](https://hsedocs.pdo.com.om/HSEDSVisioFiles/SP-2472.pdf)

**Illustrative decision:** a purchase requirement specifies a hypothetical carbon maximum of 0.030% by mass. XRF measurements agree with the expected chromium, nickel, and molybdenum ranges, but carbon is unmeasured. The conclusion is “measured alloying elements consistent; carbon requirement unresolved,” regardless of a displayed grade match. A suitable carbon-capable method and an agreed acceptance rule are still needed. This example defines a decision problem, not a grade specification or instrument accuracy claim. [Basis for the XRF carbon limitation](https://ims.evidentscientific.com/en/insights/considerations-using-xrf-pmi)

## Define the decision before choosing an instrument

Ask which elements distinguish the specified material from plausible substitutions, and at what concentrations. “Identify stainless steel” and “verify its carbon limit” are different analytical tasks. Also establish whether a test mark is acceptable, whether the location is a weld or base metal, and whether the surface can accommodate the probe. Hitachi’s PMI selection guidance explicitly separates carbon analysis, permissible marking, hot surfaces, and weld access. A convenient handheld format does not establish suitability for every task. [Hitachi PMI inspection guidance](https://hha.hitachi-hightech.com/en/product-range/applications/pmi-inspection)

A composition result alone does not demonstrate heat treatment, tensile properties, toughness, or fitness for service. Keep those acceptance questions and their required records/tests separate. As a practical reporting rule, state the chemical checks actually completed rather than declaring an entire material specification satisfied. PMI also needs component identity: PDO defines traceability as matching an installed component to its source and separately requires material certificates and material controls. [PDO SP-2472, definitions and material controls](https://hsedocs.pdo.com.om/HSEDSVisioFiles/SP-2472.pdf)

## What the principal methods measure

| Method | Useful capability | Important boundary |
| --- | --- | --- |
| Handheld X-ray fluorescence (XRF) | Nondestructive alloy chemistry and sorting using characteristic X-ray signals | Cannot directly measure carbon; coatings and surface contamination can distort the result |
| Spark optical emission spectroscopy (OES) | Elemental analysis including carbon and, with suitable equipment, low concentrations of other critical elements | Requires appropriate preparation, probe arrangement, and a permitted test location |
| Laser-induced breakdown spectroscopy (LIBS) | Analyzes light emitted by laser-generated plasma; selected instruments quantify carbon in steels | Element range and carbon capability are model/mode specific; ablation leaves a small mark |

Evident explains that handheld XRF does not directly measure elements lighter than magnesium, including carbon, lithium, and beryllium. Other measured elements may suggest a grade, but do not quantify the missing element. Its December 22, 2016 technical article also describes the shallow measurement region and the effects of paint, galvanizing, dirt, and preparation residue. Do not interpret a surface measurement as unquestioned bulk chemistry. [Evident XRF PMI considerations](https://ims.evidentscientific.com/en/insights/considerations-using-xrf-pmi)

Hitachi identifies OES as suitable for carbon, phosphorus, sulfur, and boron analysis at low detection limits. That is a technology selection lead, not a common detection limit for every instrument, alloy matrix, or probe. Request demonstrated performance for the actual element, concentration, matrix, and configuration rather than relying on an “OES” label. [Hitachi metals QA/QC technology comparison](https://hha.hitachi-hightech.com/en/campaigns/metal-analysers-for-qa/qc)

## Bounded equipment examples

Thermo Scientific’s Niton Apollo is a carbon-capable LIBS example. Its manufacturer FAQ lists low-alloy/carbon-steel and stainless-steel modes, including carbon analysis for stainless L/H grade distinctions. It requires surface preparation, and its argon purge improves analytical sensitivity. This does not imply that all handheld LIBS units measure carbon or share its performance. [Niton Apollo manufacturer FAQ](https://www.thermofisher.com/order/catalog/product/NITONAPOLLO/faqs)

The Apollo datasheet, carrying copyright 2023 and document code **NITONAPOLLO-PS-0823**, lists separate elemental ranges for those modes. It also states that users can create, clone, and edit alloy libraries. Consequently, record the active library and acceptance settings: a displayed grade name depends on configured comparisons. The same datasheet identifies a Class 3B laser and safety interlocks; use the model’s training and operating controls. [Apollo datasheet, specifications and footer](https://documents.thermofisher.com/TFS-Assets/CAD/Datasheets/niton-apollo-libs-datasheet.pdf)

For small targets, Evident’s Vanta Core product description offers an optional collimator and two cameras for positioning and documentation. Those features can help locate a test on a weld or small part; they do not establish that a particular narrow weld, curved surface, or surrounding material is analytically isolated. Verify spot geometry with the actual configuration. [Evident Vanta PMI product description](https://ims.evidentscientific.com/en/xrf-analyzers/pmi)

## Preparation and measurement controls

Prepare representative bare metal using the instrument’s approved procedure. Remove interfering coatings, rust, oil, and contamination without introducing a new contaminant. Match the prepared area to probe requirements; curved parts and welds may need adapters. Hitachi’s July 26, 2018 guidance recommends avoiding fingerprints on prepared surfaces, checking reference material before analysis, and checking OES argon supply and burn quality. A failed check calls the measurement process into question before it calls the component into question. [Hitachi PMI dos and don’ts](https://hha.hitachi-hightech.com/en/blogs-events/blogs/2018/07/26/the-dos-and-donts-of-pmi/)

Use reference checks appropriate to the intended analysis and retain their outcomes. Define repeat locations and handling of disagreement in the procedure. Additional readings can reveal local variability, but averaging readings from different materials or contaminated locations can hide the problem. Apollo supports averaged readings; that software function does not decide whether the underlying samples belong together. Its FAQ also requires affiliated safety training covering laser operation and argon handling. [Apollo measurement and training FAQ](https://www.thermofisher.com/order/catalog/product/NITONAPOLLO/faqs)

## Interpret and report without overclaiming

A useful result links component and test location to method, instrument/configuration, preparation, element results and units, checks, acceptance criteria, and disposition. Preserve unresolved or rejected status instead of silently changing the requested grade. Keep weld metal distinct from adjacent base metal. PDO’s specification illustrates why consumable chemistry may require deposited weld-metal testing when alloying additions come from flux; its detailed requirements apply within that owner’s program. [PDO SP-2472, consumable verification and reporting](https://hsedocs.pdo.com.om/HSEDSVisioFiles/SP-2472.pdf)

## Related reference

[Inspection and quality documents](../../sourcing/documents/index.md)