TWI Frequently asked questions
- It is quick and relatively uncomplicated
- It gives immediate indications of defects
- It shows surface and near surface defects, and these are the most serious ones as they concentrate stresses
- The method can be adapted for site or workshop use
- It is inexpensive compared to radiography
- Large or small objects can be examined
- Elaborate pre-cleaning is not necessary
Disadvantages of the Magnetic Particle method of Non-Destructive Examination are:
- It is restricted to ferromagnetic materials - usually iron and steel, and cannot be used on austenitic stainless steel
- It is messy
- Most methods need a supply of electricity
- It is sometimes unclear whether the magnetic field is sufficiently strong to give good indications
- The method cannot be used if a thick paint coating is present
- Spurious, or non-relevant indications, are probable, and thus interpretation is a skilled task
- Some of the paints and particle suspension fluids can give a fume or fire problem, particularly in a confined space
Books on the subject are:
- R Hamshaw, Introduction to the Non-Destructive Testing of Welded Joints, 2nd edition, Abington Publishing, Cambridge, UK, 1996 (ISBN 1 85573 314 5)
- C E Betz, Principles of Magnetic Particle Examination, published by the Magnaflux Corporation, 1967.
- Magnetic Particle Examination, NDE Monograph, published by the Non Destructive Examination Society of Great Britain, 1975
- David Lovejoy, Magnetic Particle Inspection, A Practical Guide, published by Chapman Hall, 1993
