OES Analizi | EUROLAB

What Is OES?

Optical emission spectrometry (spark OES) is an analysis method in which element concentrations are determined by resolving, by wavelength, the light emitted by atoms excited by an electrical discharge generated on the metal specimen's surface.

Purpose of OES

The purpose is to verify the material's identity and compliance by comparing the metal's chemical composition with the limits given in the material standard.

Which Products Is OES Applied To?

Steel and cast iron
Aluminium and its alloys
Copper and its alloys
Weld metal and cast parts

In Which Sectors Is OES Used?

MetalSteelMiningMachineryOil & Gas

Standards Related to OES

ASTM E415
ASTM E1086
ASTM E1251
ISO 14284

OES Conditions

Excitation: Spark discharge in an argon atmosphere
Calibration: Matrix-based calibration with certified reference materials
Number of measurements: Multiple spark points per specimen; averaged
Element range: Defined according to the alloy matrix

Equipment for OES

Spark optical emission spectrometer
Argon supply system
Specimen-preparation grinding machine
Certified reference material set

Sample Requirements for OES

The specimen surface must be flat and metallically bright
The surface must be ground to remove oxide and contamination
Specimen thickness and diameter must cover the instrument's aperture
A representative specimen must be taken per ISO 14284

Duration of OES

Typically 30–60 minutes, including specimen preparation.

OES Procedure

1The specimen is taken per ISO 14284.
2The analysis surface is ground.
3The instrument is standardised with reference materials.
4Sparks are taken at multiple points on the specimen.
5Results are averaged and compared with the material standard.

OES Acceptance Criteria

The acceptance criterion is the concentration range given for each element in the material standard (e.g. EN 10025, ASTM A36).

Evaluation of Results

Surface preparation directly affects the result. If calibration appropriate to the alloy matrix is not used, the result comes out wrong; separate programmes are required for different matrices.

OES Report

Standard applied
Specimen description and sampling location
Calibration status
Element concentrations
Assessment against the material standard

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Material product standards and procurement specifications

Pages Where This Method Is Used

Metal and Metallurgy Testing — What Does This Testing Field Cover?

The section below describes the field that the OES test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Metal and metallurgical testing determines the load a metal or a welded joint can carry, how it fails and what its internal structure looks like. The output of this family is often not about the product itself but about the identity of the MATERIAL: is the steel really of the declared grade, does the weld seam deliver the strength the design assumes, does the casting contain an unacceptable internal defect?

The practical importance of the field comes from the fact that a metal part rarely fails gradually. A plastic part deforms, ages, cracks and usually gives warning. A weld seam or a fastener, by contrast, often breaks without warning — especially where fatigue and brittle fracture are involved. That is why in fields such as pressure equipment, lifting gear, structural steel and pipelines, material testing is a requirement of REGULATION rather than of design.

The family brings together three groups of methods, and each answers a different question. Mechanical tests quantify how the material behaves under load. Non-destructive examination looks for defects without damaging the part. Metallography and chemical analysis explain why the material behaves the way it does — through grain structure, phase distribution, inclusion content and alloy composition.

The acceptance criterion for these tests almost never comes from the test standard, and this is the key to understanding the field. The test standard says how the measurement is to be made; the acceptable values come from the product standard, the material grade or the fabrication code. ISO 6892-1 tells you how to run a tensile test; EN 10025 tells you what yield strength that steel must deliver. When reading a report, the product standard it was assessed against is essential.

Sampling is an inseparable part of the result in this field. Two specimens taken from the same heat may give different values depending on the direction and location they were taken from; in rolled products, specimens parallel and perpendicular to the rolling direction produce different results. Product standards therefore also govern sampling location and orientation, and the report must document this.

Method groups in this field

Mechanical tests
Tensile, compression, bending, notch impact (Charpy), hardness (Brinell, Vickers, Rockwell), fatigue, creep and fracture toughness. These give the behaviour of the material under load in numerical form.
Non-destructive examination
Radiography, ultrasonic examination, penetrant, magnetic particle and visual examination. It looks for surface and internal defects without damaging the part and is an indispensable step in welded fabrication.
Metallography
Specimen preparation, etching and microscopic examination. Grain size, phase distribution, inclusion content, case depth and the weld heat-affected zone are assessed.
Chemical analysis
Alloy composition is verified by optical emission spectrometry and wet chemistry; confirmation of the material grade runs through this step.
Corrosion behaviour
Salt spray, pitting and crevice corrosion and intergranular corrosion tests. In stainless steels these can indicate the quality of the heat treatment.

Commonly confused in this field

A material certificate (such as EN 10204 3.1) is not a test report; it is the manufacturer's declaration. In critical applications independent verification is carried out, and the two must not be confused.
ASTM and ISO tensile tests measure the same quantities but use different specimen geometries; the results are not treated as directly equivalent, and whichever the specification calls for is the one applied.
Conversion tables between hardness and strength are APPROXIMATE. Calculating yield strength from hardness is not sufficient evidence for material acceptance.
In non-destructive examination, "no defect found" does not mean there is no defect; defects below the detection limit of the method may be present. The report must state the method applied and the sensitivity level.
A weld seam passing does not show that the welder or the procedure is qualified; these are separate processes.

Which decisions these results support

Verifying the material certificate and accepting incoming material
Approving welded fabrication; welder and procedure qualification
Manufacturing control of pressure equipment and structural components
Failure analysis and determining the root cause of field damage
Verifying heat treatment and surface treatment processes

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Frequently Asked Questions About OES

What is the difference between OES and XRF?

OES uses spark excitation and can measure light elements such as carbon, sulphur, phosphorus and nitrogen. XRF uses X-ray fluorescence; it is non-destructive but not as reliable as OES for light elements.