Magnetic Particle Inspection (MPI) Test for Welding
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- Опубликовано: 11 апр 2020
- Magnetic particle inspection (often abbreviated MT or MPI) is a nondestructive inspection method that provides detection of linear flaws located at or near the surface of ferromagnetic materials. It is viewed primarily as a surface examination method.
This method is used for the detection of surface and near-surface flaws in ferromagnetic materials and is primarily used for crack detection. The specimen is magnetised either locally or overall, and if the material is sound the magnetic flux is predominantly inside the material. If, however, there is a surface-breaking flaw, the magnetic field is distorted, causing local magnetic flux leakage around the flaw. This leakage flux is displayed by covering the surface with very fine iron particles applied either dry or suspended in a liquid. The particles accumulate at the regions of flux leakage, producing a build-up which can be seen visually even when the crack opening is very narrow. Thus, a crack is indicated as a line of iron powder particles on the surface.
Magnetic Particle Inspection (MPI) is a very effective method for location of surface breaking and slight sub-surface defects such as cracking, pores, cold lap, lack of sidewall fusion in welds etc in magnetic materials.
The method is applicable to all metals which can be strongly magnetised - ferritic steels and irons, but not generally austenitic steels.
The method of magnetisation must produce a magnetic field with lines of force at a large angle to the expected direction of the cracks to be detected, so that it is usual to apply the magnetisation more than once in different directions, for example in two directions mutually at right-angles, but methods of swinging the field direction during magnetisation are available.
The magnetisation may be produced by any of the following methods:
a) applying a permanent or electro-magnet to the surface (magnetic flow);
b) passing a large current through the specimen, or locally by means of current prods (current flow);
c) putting the specimen inside a current-carrying coil, or forming a coil around the specimen;
d) making the specimen the secondary loop of a transformer - (induced current) - suitable for ring-shaped specimens;
e) placing a current-carrying coil or loop close to the specimen surface;
f) threading a current-carrying bar through a hollow specimen.
The electric current used may be DC or AC of any waveform, but the current required to produce adequate magnetisation depends on the waveform of the supply, the magnetisation method used, and the material of the specimen. It is most important to ensure that the current used is correct for the specimen size and shape and also that the direction of the magnetic flux produced is suitable for the cracks expected.
By using a combination of two magnetic fields, a swinging or rotating magnetic flux can be produced, which will detect a crack in any orientation.
Usually the iron particles - dry powder or suspended in a liquid (magnetic ink) - are applied while the magnetising current is still flowing, but residual magnetisation is sometimes used, when the particles are applied after magnetisation. Some steels retain sufficient magnetisation for this method to be satisfactory, and in this case smaller, more portable, magnetising equipment can be used. Magnetic inks (particles suspended in a liquid) are used more widely than dry powders. They are applied by low-pressure spray, dipping or brushing; it is important to use plenty of ink and to allow time for the particles to flow over the surface and migrate to any cracks. On dark surfaces a very thin layer of white paint can be applied to give a higher contrast indication.
Fluorescent particles, which require UV-A illumination, are widely used and coloured particles are also available. The indications of cracks can be preserved by photography or by the use of peel-off transparent adhesive film. MPI methods can be applied to relatively rough and dirty surfaces, but the flaw sensitivity may be impaired. Magnetic methods for underwater applications have been developed. Only under very special conditions can sub-surface flaws be detected by MPI.
The tester needs to be fired for his complete lack of not giving a flying fuck!
haha Cool
Glad someone noticed
Many things are wrong here, if there is a crack, on the surface, HAZ, (and most likely there are) he missed almost the whole weld, i would say something but the actual guy doing the inspection does not care at all.
NDT should be carried by an honest guys and educated as well.
PS: I'm level II , in 6 methods, for over 15 years from now, both by NAS410 and ASNT/AWS.
Thanks for highlighting this.
Amazing, didn't know you can test all areas by placing magnet on once and spraying the rest...
Great point!
I think this is called sarcasm...
Positioning of yoke,yoke foot coverage, magnetizing time,
Alibaba work. Incorrect way to carry out MPI😅
Thanks for letting us know
In wheels india we checked line by line welding we got some burr also in eyes what a inspection
Thank you
MPI in progress noo good bro
Thank you for highlighting
They must be under paid.😅
He must have been asleep in class for this subject. I 🤔
From which Company????
haha
! DO NOT TEST THAT QUICKLY! the inspector isn't even looking. 😧😡
Thank you for highlighting
Not proper way for MPI. After contrast paint, allow to dry, then spray ink before magnetizing in parallel and transverse directions to check for defects.
Thanks for highlighting this.
Hope this guys are doing comedy
Haha..... Hi John Abuga, Kindly help us to notify for any errors in MPI testing. Thank you.
alibaba
haha
only discrepancy is the didn't walk the dog on the long welds in both directions.js
Couldn't understand.
Gak jelas video ko !
Thank you