Magnetic Particle Inspection 101

An Overview of MPI Non-Destructive Metal Testing

Magnetic Particle Inspection (MPI) is a non-destructive metal testing method. It is used to detect surface and near-surface discontinuities in ferromagnetic metal components. Magnetic particle inspection uses metal particles to identify cracks and other imperfections in the tested piece. This guide will provide an overview of magnetic particle inspection, including its history, benefits, and industrial applications.

Quick Glance at the Benefits of Magnetic Examination

  • Reliable: MPI is sensitive to surface and near-surface defects like cracks and seams. It consistently detects defects too minor to be seen with the naked eye.
  • Versatile: MPI can inspect a wide range of ferromagnetic components, including large and small parts, complex shapes, and pieces with rough surfaces.
  • Cost-Effective: MPI is a relatively low-cost NDT method compared to many other techniques.
  • Quick & Efficient: MPI is a very efficient form of NDT, able to be performed quickly.

History of Magnetic Particle Inspection

Magnetic Particle Testing was first developed as a non-destructive inspection (NDI) testing method in the early 20th century. By the 1930s, magnetic testing methods increasingly replaced other forms of examination. Its efficiency and effectiveness made it popular in the railroad industry to ensure metal components were cleared for safe operation.

Over the years, MPI has become a widely used method for detecting cracks, defects, and other discontinuities in commercial and industrial applications. Magnetic examination is one of the world's most commonly used NDT methods, employed as a preferred method to inspect welds, castings, forgings, automotive parts, power generation equipment, and more.

The Magnetic Particle Testing Process

The MPI testing process includes five basic steps: pre-cleaning, magnetization, application of magnetic particles, inspection/interpretation, and post-cleaning. The surface of the test material is cleaned and dried to remove any oil, grease, dirt, or other contaminants that may interfere with the testing process. A strong magnetic field is applied to the test material by passing an electric current through the material or by placing a magnetic yoke on the surface.

After the components are magnetized, fine metallic particles are applied to the test surface and are attracted to areas where a defect causes magnetic field distortions. An inspector examines the surface for any magnetic particle accumulation to determine the defects' nature and severity. After the inspection, the test material is cleaned to remove the magnetic particles.

Common Industrial Applications for Magnetic Particle Testing

Because MPI is highly effective and relatively low-cost, it is a popular NDT method for many industries. MPI is widely used in aerospace, automotive, structural steel, and other industrial environments. Specific industrial applications for magnetic particle testing include:

  • Welded components in all industries
  • Aircraft equipment, including engine components & landing gear
  • Automotive parts, including axles, crankshafts, & gears
  • Oil & gas pipelines
  • Power generation equipment
  • Public transportation & railroad equipment
  • Structural steel in bridges and buildings

Magnetic Particle Testing Compared to Other Testing Methods

In addition to magnetic particle testing, there are other forms of NDT processes, including fluorescent penetrant inspection (FPI) and radiographic metal testing (RT). While FPI, RT, and MPI are all highly effective methods for identifying defects in metal components, there are advantages unique to each process.

Advantages of MPI Compared to Other NDT Methods

  • Magnetic Particle Inspection is a quicker examination method than most NDT processes, including FPI and RT
  • With MPI, indications are quickly visible on the surface, as opposed to RT, which takes longer to analyze the testing results
  • MPI is one of the most economically friendly NDT methods
  • Non-ferrous materials like aluminum, magnesium, or certain stainless steels cannot be tested with MPI
  • MPI has limitations in detecting subsurface discontinuities compared to other NDT methods
  • Demagnetization after inspection is often required with MPI testing

Disadvantages of MPI Compared to Other NDT Methods

Get Your Metal Parts Inspected

Do you need MPI services for your metal components? At American Metal Testing, we specialize in non-destructive testing services, including magnetic particle inspection. We perform uncompromised, independent, non-destructive testing and analysis of machine parts, metal castings, and other components. We are dedicated to providing the best quality metal testing services for customers in all industrial sectors.

MPI Services that Meet ASTM & Other Industry Standards

All our testing is governed by the American Society for Testing and Materials (ASTM) International, Aerospace Material Specifications (AMS), American Society of Mechanical Engineers (ASME), Society of Automotive Engineers (SAE), American National Standards Institute (ANSI), American Welding Society (AWS), and military (MIL) specifications. Additionally, our testing laboratory is accredited by the National Aerospace and Defense Contractors Accreditation Program (NADCAP), qualifying us to provide non-destructive testing services to leading aerospace manufacturers.

Contact Us for Magnetic Particle Testing Services

Contact us to learn how we can provide you with non-destructive magnetic particle testing services. For pricing estimates on your testing requirements, request a quote online. American Metal Testing is your source for non-destructive testing.