MT · Conventional NDT
Magnetic Particle Testing
The Method
How MT works.
MT magnetizes the part under inspection. Where a surface or near-surface discontinuity interrupts the field, flux leaks from the surface and attracts fine iron particles, forming a visible indication.
Particles are applied dry or in a liquid carrier, and are either visible (color-contrast) or fluorescent under UV-A light. Field work typically uses electromagnetic yokes or prods.
Applications
Where MT is used
- Weld inspection on carbon and low-alloy steel
- Back-gouge and excavation inspection before repair welding
- Forgings, castings, and machined components
- In-service inspection for fatigue cracking
Detection capability
What MT can detect
- Surface-breaking cracks, including tight cracks
- Shallow subsurface discontinuities
- Seams and laps
- Incomplete fusion at or near the surface
Methods & Equipment
Typical equipment
- AC/DC electromagnetic yokes and prods
- Visible and fluorescent particles, wet and dry
- UV-A lamps and light meters
- Field indicators and artificial-flaw shims
Technical Considerations
Limits and requirements to plan for.
Ferromagnetic materials only
MT cannot be used on austenitic stainless steel, aluminum, copper alloys, or titanium. PT or ET is used instead.
Field direction
Discontinuities show best when roughly perpendicular to the field, so examinations are made in two directions about 90° apart.
Field verification
Yoke lifting power and field adequacy are verified with lift tests, field indicators, or shims.
Depth
Sensitivity falls off quickly below the surface. Internal flaws need UT or PAUT.
In Practice
MT in industry.
Naval shipbuilding
Hull, foundation, and piping welds, and excavations before repair.
Heavy fabrication
Production weld inspection on structural steel and machinery bases.
Maintenance
Crack detection on in-service components during outages.
How TCI Supports You
What you get from TCI.
- MT technicians experienced in production fabrication environments
- Visible and fluorescent techniques to suit the job
- Coordination with welding crews to keep repairs moving
Let's discuss your inspection requirements.
Tell us about your project, schedule, and the specifications you work to. A member of our leadership team will respond directly.