Magnetic particle test (MPI) is a method non-destructive testing Simple, cost-effective and reliable can be used to find surface and subsurface discontinuities in ferromagnetic materials such as iron (non-alloy and low-alloy steels, cast steel, cast iron) ), cobalt and nickel.

MPI . technique ARE NOT applicable on non-ferromagnetic materials such as high alloy steel (Austenitic), aluminum, copper, plastics, composites, etc.

To inspect a part using the MPI technique, that part needs to be magnetized first. If there is a discontinuity in the part, the magnetic field will propagate outward. This propagation is called flux leakage. Using a product containing fine iron particles, you can detect these areas of flux leakage.

A very simple way to determine if a part can be tested using the magnetic particle test is to use a permanent magnet to see if it is ferromagnetic. If correct, the magnet will 'stick' to the part and you can check it with MPI.

Only ferromagnetic materials can be tested using the MPI test. Materials with a major content of Iron or Cobalt or Nickel are called ferromagnetic materials.

VISCO offers visible and fluorescent magnetic particle inspection products.

Fluorescent MPI products contain pigments that fluoresce when exposed to ultraviolet (UV) radiation. Products for dry visible magnetic testing consist of colored particles that create contrast against the background. In addition, our black magnetic granule products can be easily observed on white background by coating the surface with white contrasting paint.

Fluorescent magnetic particle inspection products include:

• Fluorescent magnetic powder for wet method with water or oil base.
• Premixed oil-based fluorescent magnetic powder.
• Fluorescent magnetic powder mixed with water and additives.

Our Visible Magnetic Particle Inspection Products include:

• Dry powder.
• Pre-mixed oil-based black powder.

Products can be packaged in handy spray bottles, cans, cans and drums (depending on type).

The dry magnetic powder test is particularly suitable for testing on rough surfaces such as unpolished welds and rough castings. In addition to surface defects, dry powders can also be used to detect subsurface discontinuities.

With the dry magnetic powder method test, there is no carrier liquid in the process, so the dry powder can be used for testing on hot surfaces. However, in the absence of carrier fluid, the magnetic powder is less mobile.

VISCO offers a wide range of dry magnetic powders in different colors designed to create effective contrasts on different substrates. These powders can also be used over white contrasting paint.

When using dry powder, it is important to ensure that the surface is completely dry after cleaning. Dry powder is considered a disposable consumable and must not be reused because of the risk of contamination by dirt and moisture.

Wet magnetic particle testing involves applying magnetic particles to a part while the particles are suspended in the carrier fluid. The carrier can be oil or water.

The advantages of the wet test method are:

• Magnetic particles are easy to act evenly on the part to be tested;
• The magnetic particle mobility in the carrier fluid allows more time for the particles to find small flux leakage fields, making it possible to detect smaller discontinuities on smooth surfaces;
• Wet method MPI products are more sensitive when compared to dry powders;
• Wet MPI products are more suitable for the inspection of complex shapes.

When choosing between an oil- or water-based carrier, you need to consider:

• Surface wetting ability of the carrier;
• Safety and flammability aspects related to oil-based carrier solutions;
• Corrosion properties of water-based products.

Fluorescent MPI has better sensitivity than the visible magnetic powder method, but the cost of implementation and equipment requirements will be higher.

VISCO offers a wide range of oil-based and water-based inks for different uses.

Most fluorescent inks, pigmented visible magnetic powders, and high-sensitivity magnetic powders use different types of magnetic particles. Variants available for wet method magnetic particle inspection applications. The difference between oil-based and water-based can be summarized as follows:

The magnetic particle inspection method detects surface and subsurface defects as large as 6-8mm. To find deeper defects, it is necessary to use high currents (large Amps) to create a deeper and stronger magnetic field.

The alternating current magnetic device helps to detect surface defects. DC current better detects subsurface defects. Read more about the magnetic particle test method overview to know detail.

The surface of the part under test shall be free of any form of contamination that could affect the test, for example grease, water, dirt and other agents that may have been coated on the surface during the test. production or pretreatment. Solvent-based cleaners and surface cleaners can be used such as ZChek-CL. The presence of coating on the surface - such as white contrast paint - will not affect the test as long as the coating thickness is less than 50 µm. Coatings thicker than 50 µm may reduce the sensitivity of the test.

The mobility of particles is greatly affected by the presence of foreign substances such as dirt, rust, grease, residue, oil and water. In addition, certain anti-corrosion products can also cause false indications.

The part to be tested will need to be thoroughly demagnetized prior to magnetization as part of the MPI process. If the part retains residual magnetism (for example, magnetism generated during welding), the test sensitivity may be reduced or false indications are produced.

Water-based magnetic powders mixed with conditioners contain low levels of corrosion inhibitors. This level should be sufficient to protect components during the magnetic particle check test.

Parts corrosion can occur both before and after inspection, so you need to make sure parts are kept clean and dry. After testing the use of water-based products, ensure that excess water is removed as quickly as possible to prevent the risk of corrosion.

If you need longer lasting corrosion protection, cover cleaned parts with a temporary protective layer.

There are many reasons why the magnetic particle solution tank can be contaminated. A typical example is the oil or protective coating on the part that escapes into the solution in the bath. Over time, this degreasing effect can lead to a build-up of 'sludge' or deposits. This build-up is less likely when using an oil-based product because it is able to naturally dissolve this contaminant.

As a fix, we recommend pre-cleaning the parts using detergent and solvent-based cleaning prior to testing.

There are a number of reasons for the decline in the content of particles during magnetic particle testing, including:

• Particles are stuck to the part during inspection. In addition to the particles concentrated around the discontinuity, the particles also adhere to the surface of the part due to its surface roughness and geometrical shape.
• Overvalued magnetization, which usually occurs when a component has different thicknesses or diameters.
• Particles 'stuck' in parts of process equipment, such as pipes, filters, pumps, etc. In some cases when you first fill the tank and when re-inspection it is still necessary to replenish it. Add magnetic beads to achieve the right level.
• Dirt on details. For example, dirt in the form of oil and grease can cause particles to adhere to the part as it is removed from the bath.

Oil-based liquids such as Z801 not volatile under normal operating conditions. However, with water-based products, a low level of evaporation can be seen due to water loss and not additives such as wetting agents, corrosion inhibitors. Therefore, if it is necessary to add more water to the tub, only water should be added as the addition of additives can cause an imbalance of the solution in the tub.

The presence of coating on the surface - such as white contrast paint - will not affect the test as long as the coating thickness is less than 50 µm. Coatings thicker than 50 µm may reduce the sensitivity of the test. Pay attention to apply the contrast paint carefully and evenly.

If you need to remove white contrast paint from the part being inspected, use a wire brush or a common solvent such as acetone.

Both oil-based and water-based magnetic particle solutions have a maximum recommended use temperature of about 48°C because the particles are less stable at higher temperatures.

Along with that, it is necessary to pay attention to the flash point when using carrier oil (the lowest temperature at which a liquid can form a flammable mixture in air). According to AMS specifications, the flash point of the carrier oil should exceed 93°C. When conducting MPI, it is best to ensure that the temperature used is consistent with the above recommendations.

Under the new US and Canadian regulations, GHS, SDS no longer have an expiration date. Instead, the SDS is updated within 3 months of any new information. Therefore, MSDS found on our website is the latest update.