Ferrite Testing & Measurement

Ferrite testing and content measurement in Dubai, Abu Dhabi and across the UAE — non-destructive Feritscope measurement of ferrite content in duplex, super duplex and austenitic stainless steel welds and castings, to AWS A4.2 and ISO 8249, reported in Ferrite Number (FN) or percent ferrite. Last reviewed: August 2026.

In duplex and super duplex stainless steels the balance between ferrite and austenite is what delivers the material's properties. Too little ferrite and strength and resistance to stress corrosion cracking fall away; too much and toughness and corrosion resistance suffer. Welding is where the balance most often shifts, because heat input and cooling rate change the phase proportions in the weld metal and heat-affected zone.

Why it is measured

A duplex weld that has cooled too quickly can be ferrite-rich and brittle; one that has cooled too slowly can be austenite-rich with reduced strength and pitting resistance. In austenitic stainless, a controlled amount of delta ferrite in the weld metal resists solidification cracking, but too much compromises corrosion resistance and, in service at elevated temperature, can transform to embrittling phases.

None of this is visible. The weld looks correct, passes visual and penetrant examination, and fails in service later. Ferrite testing is how the phase balance is confirmed at the point it can still be corrected.

The method

Measurement is made by magnetic induction using a Fischer Feritscope. Ferrite is ferromagnetic and austenite is not, so the instrument's response to the magnetic properties of the surface layer gives a direct reading of ferrite content, expressed as Ferrite Number (FN) or as percent ferrite according to the calibration standard and the specification being worked to. Instruments are verified against certified ferrite standards before and after each job.

The technique is entirely non-destructive and is applied to the actual production component rather than to a sacrificial coupon. Laboratory metallography on a test specimen gives statistical assurance about a batch, but only direct measurement confirms the ferrite content of the item being delivered. Multiple readings are taken across each weld and adjacent material rather than a single spot value — ferrite content varies across a weld bead and between passes, and a single reading can pass while the weld as a whole does not.

Standards and specifications

• AWS A4.2 — standard procedure for calibrating magnetic instruments to measure delta ferrite content of austenitic and duplex ferritic-austenitic stainless steel weld metal
• ISO 8249 — determination of Ferrite Number in austenitic and duplex ferritic-austenitic stainless steel weld metal
• ASTM E562 — where point count metallography is specified for comparison or validation
• Instrument manufacturer's calibration and operating instructions
• Client and project specifications, including major operator specifications which commonly set ferrite acceptance ranges for duplex fabrication

Ferrite test acceptance criteria

Acceptance criteria are set by the client specification, applicable code and material manufacturer's requirements. Common ranges for duplex stainless weld metal are 35–65 FN or 30–70 FN depending on the specification; super duplex grades typically require tighter control. Where the specification sets a range, ITMAD reports each reading individually and states accept or reject status against it, with comment on the likely cause where results fall outside the range.

Where it applies

• Duplex and super duplex stainless steel welds, base material and heat-affected zones
• Austenitic stainless steel weld metal, where delta ferrite limits are specified
• Weld overlays and clad surfaces
• Castings and forgings in duplex grades
• Pipework, vessels, valves and fittings for sour and seawater service
• Subsea and offshore fabrication in duplex material
• Verification following heat treatment or repair welding
• Investigation of in-service cracking or corrosion in duplex components

Practical considerations

The measurement is surface-sensitive: scale, oxide, weld spatter and heavy grinding marks all interfere and are addressed before measurement. Component geometry matters too — curvature, edges and thin sections influence the reading and require the correct probe and technique. Multiple readings are taken across each weld and adjacent material, because ferrite content varies across a weld bead and between passes.

Personnel and equipment

Measurement is carried out by technicians and engineers experienced in stainless steel metallurgy, using instruments verified against certified ferrite standards before and after each job. Interpretation matters as much as the reading: whether a result indicates a welding parameter problem, a consumable issue or an incorrect heat treatment determines what the client does about it, and the report says which.

Accreditation and approvals

ITMAD is accredited to ISO/IEC 17020 as an inspection body, is an ADNOC approved inspection contractor, and is listed on the Abu Dhabi City Municipality register of Approved Third Party Inspection Bodies. Measurement is performed on site, in fabrication yards, offshore or at ITMAD premises, across Dubai, Abu Dhabi, Sharjah and the northern Emirates.

What you receive

• A report identifying each item and weld measured, by number or drawing reference
• Individual readings rather than an averaged value alone
• Results reported in FN or percent ferrite as your specification requires
• The instrument used and its calibration verification record
• Accept or reject status against the specified acceptance range
• Comment on the likely cause where results fall outside the range