Choosing the Right Method
Different crack detection methods suit different materials, defect types and access. Choosing correctly is key to reliable detection.
Method Comparison
A quick guide:
- MPI — surface cracks in steel
- Dye penetrant — surface cracks in any non-porous material
- Eddy current — surface cracks through paint
- Ultrasonic — internal and sub-surface cracks
Practical Limitations
MPI requires suitable ferromagnetic material and field direction; PT requires a clean, non-porous surface and only reveals defects open to that surface; ECT requires conductive material and can be affected by lift-off, geometry and permeability; UT depends on access, coupling, calibration, attenuation and reflector orientation. These limitations are why methods are sometimes combined.
From Indication to Decision
A method response is not automatically a rejectable crack. The report should identify the area and extent examined, method and relevant limitations. Confirmation, sizing, repair, monitoring or fitness-for-service decisions should follow the applicable acceptance criteria and responsible engineering advice.