🧲 Magnetic Particle Testing (MT)
In short
Detection of surface and near-surface discontinuities in ferromagnetic materials (steels, cast irons) using magnetic powder in external magnetic field. The test is performed according to PN-EN ISO 9934-1:2016-12; Materials: Only ferromagnetic (carbon, low-alloy steels, cast irons). The procedure comprises 10 steps (about 43 min–1 h 18 min in total); it is used for: Control of welded joints in carbon and low-alloy steels (EN ISO 17638), Testing of forgings and forged elements (crankshafts, gears), Control of steel and cast iron castings.
At a glance
- Standard: PN-EN ISO 9934-1:2016-12
- Category: Construction
- Procedure steps: 10
- Total time of stages: 43 min–1 h 18 min
- Materials: Only ferromagnetic (carbon, low-alloy steels, cast irons)
- Detection depth: Surface + near-surface (up to ~3 mm with DC)
- Field intensity: 2–6 kA/m (steels, according to ISO 9934-1)
Overview
Magnetic particle testing (MT — Magnetic Particle Testing) is a non-destructive testing method for detecting surface and near-surface discontinuities (up to depth ~3 mm) in ferromagnetic materials. Standard PN-EN ISO 9934-1 specifies general principles of the method, magnetization techniques, detection media and results assessment.
The working principle is based on distortion of magnetic field lines by a discontinuity — at the defect location a leakage field is created, which attracts fine magnetic particles (iron powder) applied to the surface. Powder accumulation forms visible indication corresponding to position and shape of discontinuity.
The method is used exclusively for ferromagnetic materials (carbon steels, low-alloy steels, cast irons) — not suitable for austenitic stainless steels, aluminum, copper or non-metallic materials. For these materials, penetrant testing (PT) is used.
Magnetization is performed with electromagnetic yokes, coils, current flow (prod) or induced current. Dry powder (black or fluorescent) or magnetic suspension (in water or oil) is used. Highest sensitivity is ensured by combination: alternating current AC + fluorescent powder + observation in UV-A.
NDT personnel must have qualifications according to PN-EN ISO 9712 (level 1, 2 or 3). MT testing is required by welding standards (EN ISO 17638), pressure equipment directive PED and industrial quality standards.
Method principle
Ferromagnetic material placed in magnetic field becomes magnetized — field lines run inside material. If a discontinuity (crack, porosity) is in the path of field lines, the lines are distorted and partly expelled outside — local leakage field is created. Fine magnetic particles (iron powder) applied to surface are attracted by leakage field and accumulate over discontinuity, forming visible indication. Detection effectiveness is highest when discontinuity is perpendicular to magnetic field direction.
Applications
- Control of welded joints in carbon and low-alloy steels (EN ISO 17638)
- Testing of forgings and forged elements (crankshafts, gears)
- Control of steel and cast iron castings
- Service testing of fatigue components (bridges, cranes, pressure vessels)
- Control of railway rails (fatigue crack detection)
- Testing of surfaces after grinding (grinding cracks)
Key parameters
| Parameter | Value |
|---|---|
| Materials | Only ferromagnetic (carbon, low-alloy steels, cast irons) |
| Detection depth | Surface + near-surface (up to ~3 mm with DC) |
| Field intensity | 2–6 kA/m (steels, according to ISO 9934-1) |
| Magnetization techniques | Yoke AC/DC, coil, current flow (AC/DC/HWDC) |
| Detection media | Dry powder (black/fluoresc.) / magnetic suspension (water/oil) |
| UV-A lighting (fluorescence) | ≥ 1000 µW/cm² at 365 nm, darkness < 20 lx |
Standard
- Standard number
- PN-EN ISO 9934-1:2016-12
- Title (PL)
- Badania nieniszczące — Badania magnetyczno-proszkowe — Część 1: Zasady ogólne
- Title (EN)
- Non-destructive testing — Magnetic particle testing — Part 1: General principles
Step-by-step procedure
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Surface preparation
Clean surface from contaminants, paint, rust, scale. Surface dry and clean. Apply contrast paint (with black powder).
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Magnetization technique selection
Select technique providing field perpendicular to expected defects. For defects of unknown orientation — magnetization in two perpendicular directions.
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Magnetic field verification
Verify field intensity with gaussmeter or using reference strip (Burmester). Tangential intensity 2–6 kA/m.
-
Detection medium application
Apply dry powder (puffer) or pour surface with magnetic suspension. With continuous method — apply DURING magnetization.
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Magnetization
Turn on electromagnet/current flow. Magnetize min. 3 × 1 s (pulsed) or continuous mode with simultaneous medium application.
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Excess removal
Gently remove excess powder / suspension (light air stream, draining). Do not remove too aggressively — indication destruction.
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Inspection and evaluation
Evaluate indications: with black powder — white light > 500 lx. With fluorescent — UV-A ≥ 1000 µW/cm², darkness < 20 lx. Classify indications (linear/rounded).
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Documentation
Prepare report: element identification, magnetization technique, medium, results, indication map, assessment according to criteria (e.g. EN ISO 23278).
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Demagnetization
Demagnetize element with demagnetizing coil. Check residual magnetism with gaussmeter (< 0.3 mT for mechanical components).
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Final cleaning
Remove contrast paint and detection medium residues. Apply anti-corrosion protection.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Electromagnetic yoke (AC yoke) | Magnaflux Y-7, Parker DA-400, Helling FA 400 | 3 000–15 000 PLN |
| Magnetizing bench (stationary) | Magnaflux Magnavis, Tiede LY-series | 50 000–200 000 PLN |
| Fluorescent magnetic suspension | Magnaflux 14A (fluorescent dry powder), 14HF (suspension) | 150–400 PLN / liter or kg |
| UV-A lamp (365 nm) | Magnaflux ZB-100F, Labino Compact UV, Helling UV-Inspector | 3 000–15 000 PLN |
| Field intensity meter | Hirst GM08 (Gaussmeter), Hall probe, Berthold indicator | 2 000–8 000 PLN |
| Reference specimens | Burmester strip type 1/2, strip A1/A2 according to ISO 9934-2 | 200–500 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Black dry magnetic powder | — | Fe₃O₄ iron powder with particle size 5–150 µm, for use on light surfaces |
| Fluorescent magnetic powder | — | Particles coated with fluorescent pigment — highest sensitivity in UV-A 365 nm |
| Suspension carrier (water/oil) | — | Water with corrosion inhibitor or light mineral oil — powder concentration 0.1–0.4 mL/100 mL (Centrifuge tube) |
| White contrast paint | — | Thin white layer under black powder — improves indication contrast (do not use with fluorescent) |
| Demagnetizer | — | Demagnetizing coil to remove residual magnetism after testing |
Health and safety (OHS)
- Magnetizing current (AC/DC) — risk of electric shock, do not touch electrodes during operation
- Electromagnetic yoke — strong magnetic field, prohibited for people with pacemakers
- Magnetic powder — avoid inhalation (dust mask) and eye contact
- UV-A lamp — do not look directly, protective glasses
- Oil-based suspensions — flammable, ventilation, no open flame
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 9934-1:2016-12 — “Non-destructive testing — Magnetic particle testing — Part 1: General principles”.
How does this method work?
Ferromagnetic material placed in magnetic field becomes magnetized — field lines run inside material. If a discontinuity (crack, porosity) is in the path of field lines, the lines are distorted and partly expelled outside — local leakage field is created.
What is the measuring range and accuracy?
Materials: Only ferromagnetic (carbon, low-alloy steels, cast irons); Detection depth: Surface + near-surface (up to ~3 mm with DC); Field intensity: 2–6 kA/m (steels, according to ISO 9934-1); Magnetization techniques: Yoke AC/DC, coil, current flow (AC/DC/HWDC).
How long does the test take?
The times given for the individual stages add up to approximately 43 min–1 h 18 min. The procedure comprises 10 steps.
What equipment is required?
Electromagnetic yoke (AC yoke), Magnetizing bench (stationary), Fluorescent magnetic suspension, UV-A lamp (365 nm), Field intensity meter, Reference specimens. Indicative cost of the core instrument (Electromagnetic yoke (AC yoke)): 3 000–15 000 PLN.
Where is this test used?
Control of welded joints in carbon and low-alloy steels (EN ISO 17638); Testing of forgings and forged elements (crankshafts, gears); Control of steel and cast iron castings; Service testing of fatigue components (bridges, cranes, pressure vessels); Control of railway rails (fatigue crack detection); Testing of surfaces after grinding (grinding cracks).
What safety precautions apply?
Magnetizing current (AC/DC) — risk of electric shock, do not touch electrodes during operation; Electromagnetic yoke — strong magnetic field, prohibited for people with pacemakers; Magnetic powder — avoid inhalation (dust mask) and eye contact; UV-A lamp — do not look directly, protective glasses; Oil-based suspensions — flammable, ventilation, no open flame.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 9934-1.