Ferrite Content Measurement

Non-Destructive Ferrite Number (FN) and Ferrite Content Assessment of Stainless Steel Welds and Components

AECTL provides non-destructive ferrite and magnetic-phase measurement in steels with austenitic microstructures, including austenitic and duplex stainless steel welds, weld overlays, claddings and suitable components.

The system is particularly suited to measurement of Ferrite Number (FN) and ferrite-related magnetic response in stainless steel weld metal, as well as detection of ferromagnetic phases such as strain-induced martensite in austenitic stainless steels. Measurements can be undertaken in the laboratory or directly on accessible components in the field for welding procedure qualification, fabrication quality control, production weld inspection and materials condition assessment.

The method is fast, non-destructive and suitable for both laboratory and on-site work, allowing measurements to be taken directly on accessible welds and components without sectioning the material.

Why Ferrite Content Matters

The balance between austenite and ferritic phases can strongly influence the performance of stainless steel welds and duplex stainless steel components. In austenitic stainless weld metal, a controlled amount of delta ferrite can reduce susceptibility to solidification cracking. Excessive ferrite, however, may reduce toughness, ductility or corrosion performance and may increase the risk of undesirable phase transformation during elevated-temperature exposure.

For duplex stainless steels, phase balance is particularly important because mechanical properties and corrosion resistance depend on maintaining an appropriate balance between ferrite and austenite. The acceptable ferrite range is therefore application- and specification-dependent and should be assessed against the governing welding procedure, material specification or project requirement rather than against a universal limit.

How the FERITSCOPE Measurement Works

magnetic field generated by the probe interacts with magnetisable phases in the material. The instrument evaluates the resulting change in the magnetic field and converts it to a ferrite-related measurement.

An important technical limitation is that magnetic-induction measurement responds to magnetisable microstructural constituents. It therefore does not identify delta ferrite alone. Strain-induced martensite and other ferromagnetic phases can also contribute to the reading. Where the distinction between phases is important, the result should be interpreted together with metallography or other suitable materials-characterisation methods.

Ferrite and Martensite Measurement

The magnetic induction method responds to ferromagnetic constituents within an otherwise predominantly austenitic microstructure. In addition to delta ferrite, this can include strain-induced martensite formed by cold working or deformation of austenitic stainless steel.

The FERITSCOPE result should therefore be understood as a magnetic response associated with these phases rather than direct microscopic identification of delta ferrite alone. Where individual phases must be distinguished or directly quantified, AECTL can supplement FERITSCOPE measurements with metallographic examination and quantitative image analysis.

Applicable Standards

The applicable standard depends on whether the requirement is for weld metal Ferrite Number, ferrite-content verification of duplex material, a welding procedure qualification, or a project-specific inspection requirement.

· ISO 8249:2018 – Welding – Determination of Ferrite Number (FN) in austenitic and duplex ferritic-austenitic Cr-Ni stainless steel weld metals. This is the principal current international reference for FN measurement and instrument calibration for stainless steel weld metal.

· AWS A4.2M:2020 (ISO 8249:2018 MOD) – Standard procedures for calibrating magnetic instruments used to measure delta ferrite in austenitic and duplex ferritic-austenitic stainless steel weld metal.

· Project, client, welding procedure or fabrication specifications that nominate ferrite-number limits, measurement locations or minimum measurement frequency.

Older documents may refer to DIN EN ISO 17655:2003 for delta-ferrite determination. That standard has been withdrawn, and current work should preferentially reference the applicable current standard or project specification. AECTL can review legacy drawing or specification references before testing.

Typical Components and Applications

Austenitic stainless steel weld metal.

Duplex and super duplex stainless steel welds.
Stainless steel pipe and tube welds.
Pressure vessels, boilers and process equipment.
Austenitic weld overlays and claddings.
Chemical and petrochemical plant equipment.
Water and wastewater process equipment.
Power-generation and energy-sector components.
Fabricated tanks and stainless steel structures.
Welding procedure qualification and production quality-control samples.
Austenitic cladding and weld overlays.
Weld seams in stainless steel pipes and tubes.
Boilers and pressure equipment.
Chemical and petrochemical processing equipment.
Oil and gas infrastructure.
Mechanical engineering and steel-construction components.
Construction and infrastructure applications.
Research and laboratory investigations.
Location of weld seams on polished austenitic stainless steel surfaces where a measurable magnetic-property difference is present.

Industries We Support

Ferrite and magnetic-phase measurement can support fabrication, inspection, quality control and materials investigations across:

Oil and gas.
Petrochemical and chemical processing.
Power generation and energy.
Pressure equipment and boiler fabrication.
Mechanical engineering.
Steel construction.
Construction and infrastructure.
Water and wastewater.
Manufacturing and fabrication.
Research and development.
Materials testing and laboratory investigations

On-Site Ferrite Measurement

AECTL’s portable ferrite measurement service enables on-site ferrite testing of accessible welds and components at fabrication workshops, construction sites, and operational facilities. This non-destructive method allows production welds to be verified without removing material, making it an ideal solution where laboratory sampling is impractical or rapid in-field verification is required.

For reliable field measurement, the test surface should be accessible, reasonably clean and suitable for stable probe contact. Curvature, component thickness, surface roughness, geometry and probe orientation can influence the result and should be considered when planning the measurement.

Factors That Can Affect Ferrite Measurements

Surface curvature – measurements on concave or convex surfaces can be biased if calibration and geometry are not appropriately considered.
Component thickness and edge effects – very thin or small components can alter the magnetic field and influence readings.
Surface roughness – rough surfaces can cause variation depending on whether the probe contacts a peak or valley.
Probe position and tilt – the probe should be placed consistently and without unnecessary pressure.
Weld geometry – narrow beads, irregular caps and heat-affected geometries may require careful selection of measurement points.
Presence of strain-induced martensite or other magnetic phases – these can contribute to the indicated magnetic response.

For this reason, ferrite assessment should generally be based on a defined measurement plan and a suitable number of readings rather than a single isolated value.

Ferrite Number (FN) Versus Percent Ferrite

Ferrite Number (FN) and percentage ferrite (%Fe) are not interchangeable values. FN is a standardised magnetic-response scale widely used for stainless steel weld metal. Although ferrite can be reported as either FN or %Fe, contractual and acceptance decisions should be based on the parameter specified in the governing standard or project specification.

Where a project requires Ferrite Number, AECTL reports FN using the applicable calibration basis. Where percentage ferrite is requested, the measurement method and reporting basis are clearly identified.

Laboratory and Field Applications

Welding Procedure Qualification

Measure ferrite in deposited weld metal during procedure qualification where the applicable welding or project specification requires an FN range.

Production Weld Inspection

Verify ferrite number at nominated production welds as part of fabrication quality assurance and inspection.

Duplex Stainless Steel Assessment

Use non-destructive ferrite measurement as a rapid screening and quality-control tool for duplex stainless steel welds and suitable components, with metallography available where direct phase quantification or microstructural confirmation is required.

Weld Overlay and Cladding

Assess ferrite response in austenitic claddings and weld overlays where ferrite control is specified for corrosion resistance, fabrication or service performance.

Failure and Condition Investigation

Combine ferrite measurement with metallography, hardness, chemistry or microscopy where abnormal material performance, cracking, embrittlement or phase-balance concerns are being investigated.

Reporting

Depending on the agreed scope, AECTL reporting can include:

Component, weld and measurement-location identification.
Applicable standard, project specification or client requirement.
Instrument and probe identification.
Calibration/verification information relevant to the measurement.
Individual Ferrite Number or %Fe readings.
Average, minimum and maximum results where applicable.
Photographic documentation of measurement locations.
Comparison with nominated acceptance criteria.
Engineering comments and interpretation where required.

Ferrite Measurement as Part of a Broader Materials Assessment

Magnetic ferrite measurement is an efficient non-destructive method, but it does not replace every form of microstructural assessment. Where a project requires direct phase identification or a detailed metallurgical investigation, AECTL can combine ferrite measurement with complementary techniques.

Metallographic preparation and optical microscopy.
Duplex stainless steel phase-balance assessment by image analysis where applicable.
Chemical composition verification.
Hardness testing.
SEM/EDS examination.
Weld failure investigation.
Corrosion and materials-condition assessment.

Why AECTL?

AECTL combines portable ferrite measurement with materials engineering and metallurgical investigation capability. This allows the test to be treated as more than a stand-alone instrument reading: weld condition, material grade, project specification, phase balance and service requirements can be considered when interpretation is required.

Request Ferrite Content Measurement

For an accurate quotation, please provide the material grade, component or weld type, applicable standard or project specification, required ferrite range, number and location of measurements, and whether testing is required in the laboratory or on site. Welding procedure specifications, drawings and photographs are useful where available.

Advanced Engineering Consultancy & Testing Laboratory (AECTL)
14 Garling Road, Kings Park NSW 2148
Phone: 02 8201 3560
Email: enquiries@aectl.com.au