What Is Radiation:

What Is Radiation:

X and Gamma Rays are a family of waves that are called electromagnetic waves. X-rays and gamma rays differ only in their source of origin.  X-rays are produced by an x-ray generator and gamma radiation is the product of radioactive atoms.  They are both part of the electromagnetic spectrum. They are waveform, as are light rays, microwaves, and radio waves. X-rays and gamma rays cannot been seen, felt, or heard. They possess no charge and no mass and, therefore, are not influenced by electrical and magnetic fields and will generally travel in straight lines. However, they can be diffracted (bent) in a manner similar to light.

Magnetic Particle Test Process

1. A suitable technique of magnetization is chosen.
2. The part is magnetized in the desired direction.
3.  While the magnetizing field is present, iron powders
are applied dry or wet.
4.  Iron powders bridge the leakage fields, if present, to produce
5.  Powder patterns produced by flaws are identified and
accept reject decision is made.

MPT Process.jpg

Advantages & Limitation of MPT

Advantages Of MPT:

1.Detects flaw below ¼” below surface.

  1. Detects flaw filled with foreign material.
  2. Detect defect below painted & platted surface.
  3. Immediate indication.
  4. Testing is possible up 300°C using dry powder.
  5. Indication can recorded.

Limitation of MPT :

1.Applicable to only ferromagnetic material only.

2.Limited depth of detection.

3.Depth & size is not indicated.

4.Sensitivity varies with surface roughness & position.

5.Sensitivity rapidly diminishes with depth.

Detection of leakage field :

Detection of leakage field :
Finely divided iron particles are used for detection of leakage field. Leakage  field at the surface collects and hold the iron particles together to form visible indication patterns.

  • Flaws at or near the surface disturb the magnetic flux flow and produce leakage field at surface above the flaw.
  • Magnetic particle build up at the leakage field produces recognizable patterns which are interpreted.
  • Color of the particles must be chosen to provide adequate contrast against the part’s natural color.

Discontinuities at or near the surface produce magnetic leakage field on the surface

Discontinuities at or near the surface produce magnetic leakage field on the surface :
Magnetic flux in a magnetized part pass through the body of the part. Discontinuities at or near the surface of the part disturb the normal flow of magnetic flux and leakage flux fields are produced on the surface above the discontinuities. These leakage fields attract  iron particles and are detected by applying iron powders.

Magnetic Particle Testing

  • When a ferromagnetic material is magnetised the flux lines flow inside the component

  • When there is a discontinuity in the material there is flux leakage

  • The leaking flux attracts a magnetic medium resulting in an indication.

What is magnetic particle testing?

What is magnetic particle testing?

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.

Post Emulsifiable Penetration System

Post emulsifiable Penetration System:

Post emulsifiable lipophilic/ hydrophilic   methods  are  formulated  to  maximize   penetrating  and  visibility characteristics.    They  do  not  contain  any  emulsifying  agent in penetrant   and  cannot  be  completely  removed  with  plain  water.

Post emulsifiable lipophilic: Removal  is  made  possible  by  applying  an  emulsifier  in  a  separate  process  step after dwell time for penetrant.    This  converts  the  excess  surface penetrant into an water washable penetrant . This emulsifier uses diffusion method to convert penetrant in to water washable.

Post Emulsifiable Hydrophilic Method: The  hydrophilic postemulsifiable, method also uses penetrants requiring a separate emulsifier.  The penetrants are the same  as  those  used  in  the  lipophilic  method.    The  difference  between  hydrophilic  and  lipophilic  methods  is  in  the emulsifiers.    Hydrophilic  emulsifiers  are  water  soluble  emulsifiers  and  actually  remove  excess  surface  penetrant  by means of a scrubbing  action rather than diffusion action.