IRAM 125 Non-destructive testing of superficial and subsurface defects. Determination method by magnetiz-POR-PART%C3%8DCULAS-MAGN%C3%89TIC particles INSPECTION BY MAGNETIC PARTICLES].

The non-destructive magnetic particle testing method is used to detect possible discontinuities in the inspection of ferromagnetic materials. The magnetic particle technique is a relatively simple non-destructive technique, based on the property of certain materials to become a magnet.

Scope..

It is a method that mainly uses electric current to create a magnetic flux in a piece and when applying a ferromagnetic powder it produces the indication where there is distortion in the flow lines (field leakage). This procedure is used for the detection of surface and subsurface discontinuities (up to approximately 1/4" deep, for practical situations) in ferromagnetic materials. Physical property on which it is based. (Permeability).

• - Property of some materials to be magnetized.

• - The characteristic of flow lines of altering their trajectory when they are intercepted by a change in permeability.

Materials are classified as:.

• - Diamagnetic: They are slightly repelled by a magnetic field, they magnetize poorly.

• - Paramagnetic: They are slightly attracted by a magnetic field, They are not magnetized.

• - Ferromagnetic: They are easily attracted by a magnetic field, they are easily magnetized.

Types of discontinuities:.

• - Superficial.

• - Subsurface (very close to the surface) Pores, cracks, sinkholes, overlaps, seams, laminations, etc.

Advantages.

• - Serial parts can be inspected, obtaining safe and immediate results during the process.

• - Inspection is faster than penetrating liquids and more economical.

• - Relatively simple equipment, provided with controls to adjust the current, and a visible ammeter, connectors for HWDC, FWDC and AC.

• - Portability and adaptability to small or large samples.

• - Requires less cleaning than Penetrating Liquids.

• - Detects both surface and subsurface discontinuities.

• - Indications are produced directly on the surface of the part, indicating the length, location, size and shape of the discontinuities.

• - The equipment does not require extensive maintenance.

• - Better examination of discontinuities that are full of carbon, slag or other contaminants and that cannot be detected with a Penetrating Liquid inspection.

Disadvantages.

• - It is applicable only to ferromagnetic materials; In welding, the deposited metal must also be ferromagnetic.

• - Requires a power source.

• - Uses iron particles with a 100 mesh (0.150 mm) sieve.

• - It will not detect discontinuities that are at depths greater than 1/4".

• - The detection of a discontinuity will depend on many variables, such as the permeability of the material, type, location and orientation of the discontinuity, amount and type of magnetizing current used, type of particles, etc.

• - The application of the method in the field is more expensive.

• - Surface roughness can distort flow lines.

• - Two or more sequential inspections with different magnetizations are required.

• - Generally, demagnetization is required after inspection.

• - Care must be taken to avoid electric arc burns on the surface of the piece with the contact tip technique.

Inspection Procedure.

Test Area: The test area must include the area of ​​the point to be tested and extend an additional inch around it. For a weld, the test area must include the weld bead, the heat affected zone (HAZ), and up to one inch on either side of the weld.

Test time: The final magnetic particle test will be carried out when the part being inspected is in its final operating condition, that is, after heat treatment, machining or prepared for final finishing.

Temperature during test: A magnetic particle test should not be performed on a surface that exceeds 65°C (135°F).

Test method: The test must be developed using the continuous method; This means that the magnetizing current must remain while the particles are applied to the surface of the part and while the excess particles are being removed.

Direction of magnetization: At least two separate inspections must be performed on each part or test area. The second inspection must be with the magnetic flux lines perpendicular to the one carried out in the first inspection in the same area.

Magnetizable particles must be small in size to have good resolution, that is, to detect small or deep defects. This is because the larger the size of the particle, the larger the field needed to rotate it. However, they should not be too small so that they do not accumulate on surface irregularities, causing erroneous readings. Therefore, it is usual to combine small particles (between 1 μm "Micrometer (unit of length)") and 60 μm "Micrometer (unit of length)") and large particles (from 60 μm "Micrometer (unit of length)") to 150 μm "Micrometer (unit of length)") in the same test).

As already mentioned, the magnetizable particles can be applied in powder form or in suspension in a liquid. In the latter case, the liquid used can be kerosene, water or oil, among others.

IRAM 125 Non-destructive testing of superficial and subsurface defects. Determination method by magnetiz-POR-PART%C3%8DCULAS-MAGN%C3%89TIC particles INSPECTION BY MAGNETIC PARTICLES].

The non-destructive magnetic particle testing method is used to detect possible discontinuities in the inspection of ferromagnetic materials. The magnetic particle technique is a relatively simple non-destructive technique, based on the property of certain materials to become a magnet.

Scope..

It is a method that mainly uses electric current to create a magnetic flux in a piece and when applying a ferromagnetic powder it produces the indication where there is distortion in the flow lines (field leakage). This procedure is used for the detection of surface and subsurface discontinuities (up to approximately 1/4" deep, for practical situations) in ferromagnetic materials. Physical property on which it is based. (Permeability).

• - Property of some materials to be magnetized.

• - The characteristic of flow lines of altering their trajectory when they are intercepted by a change in permeability.

Materials are classified as:.

• - Diamagnetic: They are slightly repelled by a magnetic field, they magnetize poorly.

• - Paramagnetic: They are slightly attracted by a magnetic field, They are not magnetized.

• - Ferromagnetic: They are easily attracted by a magnetic field, they are easily magnetized.

Types of discontinuities:.

• - Superficial.

• - Subsurface (very close to the surface) Pores, cracks, sinkholes, overlaps, seams, laminations, etc.

Advantages.

• - Serial parts can be inspected, obtaining safe and immediate results during the process.

• - Inspection is faster than penetrating liquids and more economical.

• - Relatively simple equipment, provided with controls to adjust the current, and a visible ammeter, connectors for HWDC, FWDC and AC.

• - Portability and adaptability to small or large samples.

• - Requires less cleaning than Penetrating Liquids.

• - Detects both surface and subsurface discontinuities.

• - Indications are produced directly on the surface of the part, indicating the length, location, size and shape of the discontinuities.

• - The equipment does not require extensive maintenance.

• - Better examination of discontinuities that are full of carbon, slag or other contaminants and that cannot be detected with a Penetrating Liquid inspection.

Disadvantages.

• - It is applicable only to ferromagnetic materials; In welding, the deposited metal must also be ferromagnetic.

• - Requires a power source.

• - Uses iron particles with a 100 mesh (0.150 mm) sieve.

• - It will not detect discontinuities that are at depths greater than 1/4".

• - The detection of a discontinuity will depend on many variables, such as the permeability of the material, type, location and orientation of the discontinuity, amount and type of magnetizing current used, type of particles, etc.

• - The application of the method in the field is more expensive.

• - Surface roughness can distort flow lines.

• - Two or more sequential inspections with different magnetizations are required.

• - Generally, demagnetization is required after inspection.

• - Care must be taken to avoid electric arc burns on the surface of the piece with the contact tip technique.

Inspection Procedure.

Test Area: The test area must include the area of ​​the point to be tested and extend an additional inch around it. For a weld, the test area must include the weld bead, the heat affected zone (HAZ), and up to one inch on either side of the weld.

Test time: The final magnetic particle test will be carried out when the part being inspected is in its final operating condition, that is, after heat treatment, machining or prepared for final finishing.

Temperature during test: A magnetic particle test should not be performed on a surface that exceeds 65°C (135°F).

Test method: The test must be developed using the continuous method; This means that the magnetizing current must remain while the particles are applied to the surface of the part and while the excess particles are being removed.

Direction of magnetization: At least two separate inspections must be performed on each part or test area. The second inspection must be with the magnetic flux lines perpendicular to the one carried out in the first inspection in the same area.