The Magnetic Particle Inspection (MT) Process is a low cost method of performing a non-destructive examination (NDE) of ferromagnetic material. Magnetism has been used to check for defects as early as 1868, when it was used to check for cracks in magnetized cannon barrels using a compass. Magnetic Particle Inspection is a moderately simple concept. It is the process of looking for leakage in magnetic flux field. Once the part being tested is magnetized, it becomes polarized – the north pole being where the magnetic force exits, and the south pole where it enters. An example of this can be seen with a magnet that is broken in half. Each piece is a complete magnet with a north and south pole. Similarly, if there is a crack on the surface, poles will start to form on either side. The magnetic field around the crack will change, exiting at the north and reentering at the south pole. When this field spreads out, it gives a similar appearance to leaking out of the material, and is therefore called a magnetic flux leakage field. The crack or flaw causing this disruption in the magnetic field is called a “discontinuity”.
The process of Magnetic Particle Inspection is relatively straightforward; however surface preparation is a critical first step. This generally requires a chemical cleaning process using soaps, organic solvents, descaling solutions, or other processes. Next a magnetic field must be introduced into the part. Once the part is magnetized, small ferromagnetic particles such as iron powder are added. The excess is carefully removed, usually by some form of air stream. Afterwards, the part is inspected for any indications of cracks. Any area where the ferromagnetic material remains indicates a defect. Finally, the part must be rotated 90 degrees and the process repeated, because discontinuities parallel to the lines of magnetic flux will not result in leakage. The primary advantages to using Magnetic Particle Inspection are speed of the examination, the low cost of the process, and the fact that defect indications are directly visible on the material’s surface.
Electrolurgy uses state-of-the-art Magnaflux test units, and we are equipped to provide fast, efficient, and accurate Magnetic Particle Inspection services. For more information about Magnetic Particle Inspection process, please contact us directly.
The Fluorescent Penetrant Dye (FP) process is one of the oldest forms of non-destructive testing. It is widely used due to the ease of the process and because it can be used on almost any material. Liquid Penetrant Dye testing uses capillary action to reveal surface breaks and makes the flaws appear larger. It provides high contrast between background and the indicator, making defects easier to identify.
The Fluorescent Penetrant Dye process requires a clean surface; it is crucial that there is no water, grease, or any other contaminant that could prevent the penetrant from entering and exposing flaws. Once the Penetrant Dye is applied, it must be left on the part long enough to allow it to seep into any defects. This time period is known as the “Dwell Time”, and is determined by the type of penetrant and the material being tested. Optimizing the dwell time requires a thorough understanding of how different types of Penetrant Dye work with different materials. At the end of the dwell period, the extra penetrant is removed from the surface, frequently with a water spray. This must be done very delicately as not to remove any from the cracks. Afterwards, a thin coating of a substance known as developer is added in order to pull the penetrant to the surface, making it visible under proper lighting conditions. After a few minutes, the part is ready to be inspected for defects.
At Electrolurgy, we hold various certifications for dye penetrant inspection, and specialize in the testing of critical components for demanding industries such as Aerospace. We offer several variations, including water washable, lipophilic, and hydrophilic penetrant methods to accommodate a wide range of materials, discontinuity types, and sensitivity requirements.
Electrolurgy is an industry leader in Non-Destructive Testing (NDT) services, delivering the highest quality products to our customers since 1969. Call or contact us today to speak to an Electrolurgy specialist about Magnetic Particle or Fluorescent Penetrant Inspection or any of our other services.