Magnetic Particle Testing (MT)
Detecting surface and near-surface flaws in ferromagnetic materials using magnetic particles.
A Proven Method for Surface Flaw Detection
Magnetic Particle Testing (MT) is one of the five conventional non-destructive testing methods and one of the most widely used techniques for detecting surface and near-surface discontinuities in ferromagnetic materials. If you are inspecting structural steel, pipeline welds, pressure vessels, or any component made from carbon steel, low-alloy steel, or iron alloys, MT is the fast, cost-effective method for finding cracks before they propagate.
Surface and near-surface cracks in structural steel can propagate under cyclic loading — wind, traffic, thermal expansion — growing until the member fails. In pipelines and pressure equipment, the same cracks can lead to leaks or rupture under operating pressure. MT finds these defects while they are still manageable, before they become safety incidents or emergency shutdowns.
MT is fast, portable, and relatively inexpensive compared to other NDT methods. It can be performed on-site or in the workshop, on components ranging from small machined parts to large structural assemblies. Clearscope provides qualified MT inspection as part of our broader NDT and quality assurance programmes. Whether you need individual weld inspection or a systematic MT programme integrated into your factory production control, we deliver results you can certify against.
How Magnetic Particle Testing Works
The MT process follows a five-step sequence — from surface preparation through to demagnetisation after inspection.
Surface Preparation
The test surface is cleaned to remove oil, grease, scale, and loose debris. A clean surface ensures particles can move freely and cluster at genuine discontinuities rather than surface contamination.
Magnetisation
A magnetic field is applied to the component using a yoke, prods, or coil. The method of magnetisation is selected based on the part geometry and the orientation of expected defects.
Particle Application
Fine ferromagnetic particles — dry powder or suspended in a liquid carrier — are applied to the magnetised surface. Fluorescent particles may be used under UV light for enhanced sensitivity.
Inspection
Where a surface or near-surface discontinuity interrupts the magnetic field, particles accumulate and form a visible indication. The inspector evaluates each indication against the applicable acceptance criteria.
Demagnetisation
After inspection, the component is demagnetised to prevent residual magnetism from interfering with subsequent manufacturing processes, welding, or service performance.
Defects Detected by MT
Fatigue cracks, stress corrosion cracks, and grinding cracks that break the surface.
Non-metallic inclusions trapped just below the surface during manufacturing.
Longitudinal discontinuities from the rolling or forging process.
Folds of metal pressed into the surface during forming or rolling operations.
Discontinuities caused by metal folding over during casting without fusing.
Toe cracks, undercut, incomplete fusion, and other surface-breaking weld discontinuities.
Where MT Is Used
Magnetic particle testing is applied across industries where ferromagnetic steels and alloys must be verified for surface integrity.
Inspection of welded connections, base plates, and load-bearing members in steel structures fabricated to EN 1090.
Detection of fatigue cracks and stress corrosion cracking in pipeline girth welds and fittings.
In-service inspection of pressure vessels and boiler components for surface-breaking defects under PED and EN 13445.
Quality control of castings, forgings, and machined components during production and final inspection.
Critical component inspection where surface integrity directly affects safety and fatigue life.
Applicable Standards
The primary standard for magnetic particle testing — covering general principles, detection media, and equipment. This standard defines how MT should be performed across all applications.
Specific to magnetic particle testing of welds. Defines the techniques and acceptance levels for MT inspection of fusion welds in metallic materials.
How Clearscope Helps
What we deliver — specific, practical, and built to hold up under audit.
Portable MT Inspection
Lightweight, portable equipment brought to your site, workshop, or operating facility — no need to move heavy components to a test lab.
Yoke & Prods Methods
Electromagnetic yoke for surface inspection and prods for larger components — method selected based on part geometry and defect orientation.
Fluorescent & Visible Particles
Both fluorescent particles under UV light for maximum sensitivity and visible particles for daylight inspection — chosen to match your inspection environment.
Demagnetisation
Post-inspection demagnetisation to remove residual magnetism that could interfere with welding, machining, or service performance.
Reporting to EN ISO 9934/17638
Full inspection reports documented to EN ISO 9934 and EN ISO 17638, with indication mapping, acceptance determination, and photographic evidence.
Need magnetic particle testing?
Our qualified technicians detect surface and near-surface flaws in ferromagnetic components. Talk to us about your inspection requirements.