Non-destructive testing (NDT)

Magnetic particle testing is a method used to detect surface defects. The defects do not have to be visible on the surface.

Scientific Basis

When a magnetic flux is applied to the inspection surface, leakage flux is generated over the discontinuities on the surface, depending on the location of the discontinuities. If ferromagnetic particles are sprinkled on the inspection surface, these particles are attracted to the discontinuities by the leakage flux. This way, the locations of the discontinuities can be detected.

Applications

It can be applied to all ferromagnetic materials.

Limitations

It cannot be applied to non-ferromagnetic materials. Discontinuities cannot be detected if they are not positioned at an angle suitable for the magnetic field. Very high magnetization currents may be required for large parts. If the inspection surface is very rough, there may be adverse effects. If there is paint or coating on the inspection surface, the thickness of this material directly affects the inspection result. Additional processes such as magnetization removal and final cleaning are generally required after inspection.

Procedure

1. Pre-cleaning of the inspection surface
2. Demagnetization if necessary
3. Application of magnetizing current
4. Spraying of ferromagnetic particles
5. Cutting off the magnetizing current
6. Examination
7. Evaluation and report preparation
8. Magnetization removal and final cleaning

EN and ISO Standards Used

• EN ISO 9934-1 - Non-destructive testing - Magnetic particle testing - Part 1: General principles
• EN ISO 9934-2 - Non-destructive testing - Magnetic particle testing - Part 2: Detection media
• EN ISO 9934-3 - Non-destructive testing - Magnetic particle testing - Part 3: Equipment
• EN ISO 3059 - Non-destructive testing - Penetrant and magnetic particle testing - Viewing conditions
• EN 1330-7 - Non-destructive testing - Terminology - Part 7: Terms used in magnetic particle testing
• EN ISO 16828 - Non-destructive testing - Ultrasonic testing - Time of flight diffraction technique as a method for the detection and sizing of discontinuities

Source

• EN ISO 17638 - Non-destructive testing of welds - Magnetic particle testing
• EN ISO 23278 - Non-destructive testing of welds - Magnetic particle inspection - Acceptance levels

Castings

• EN 1369 - Castings - Magnetic particle testing

Steel forgings

• EN 10228-1 - Non-destructive testing of steel forgings - Part 1: Magnetic particle inspection

Steel pipes

• EN ISO 10893-4 - Non-destructive testing of steel pipes - Part 5: Magnetic particle inspection of seamless and welded ferromagnetic steel tubes for the detection of surface imperfections