Magnetic Particle Inspection (MPI) is a non-destructive testing method that can detect surface and subsurface flaws in ferromagnetic materials. Magnetic particle inspection is often carried out to help determine an item’s fitness for use or conformity.

The magnetic particle test method of Non-Destructive Examination was developed in the USA, in the 1930s, as a way to check steel components on production lines. The principle of the method is that the specimen is magnetised to produce magnetic lines of force, or flux, in the material.

Magnetic Particle Inspection is performed in four steps:

1. Induce a magnetic field in the specimen.
2. Apply magnetic particles to the specimen’s surface.
3. View the surface, looking for particle groupings that are caused by defects.
4. Demagnetize and clean the specimen.

Magnetic particle users outside the aerospace industry have typically used ASTM E709 Standard Guide for Magnetic Particle Testing as their baseline standard for procedures. That’s why there are also Standard Practices like ASTM E1444 Standard Practice for Magnetic Particle Testing.

Magnetic particle inspection is used for detecting defects (discontinuities in surfaces and shallow subsurfacaes) in ferromagnetic materials. By magnetization of the inspected area there is created a magnetic field. Magnetic flux does not change its direction in the defect-free area of the tested item.

NDT (Non-Destructive Testing) refers to an array of inspection techniques that allow inspectors to collect data about a material without damaging it. It refers to an array of inspection methods that allow inspectors to evaluate and collect data about a material, system, or component without permanently altering it.

Disadvantages of the Magnetic Particle method of Non-Destructive Examination are:

• It is restricted to ferromagnetic materials – usually iron and steel, and cannot be used on austenitic stainless steel.
• It is messy.
• Most methods need a supply of electricity.

Liquid Penetrant Testing (PT) is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

A magna flux test, also known as a magnetic particle Inspection (MPI), is a non-destructive testing (NDT) process for detecting surface, and slightly subsurface, discontinuities in ferromagnetic materials such as: iron, nickel, cobalt, and some of their alloys.

Ultrasonic nondestructive testing, also known as ultrasonic NDT or simply UT, is a method of characterizing the thickness or internal structure of a test piece through the use of high frequency sound waves.

The Best NDT Method for Welding While many methods of nondestructive testing can detect failure-predictive flaws in welds, the most efficient, effective method is phased array ultrasonic testing.

NDT is used in a very wide range of industries such as; Oil & Gas, Aerospace, Energy, Power, Nuclear, Transport and job opportunities are virtually limitless. A career in NDT is extremely dynamic, where up-to-date training is a necessity.

In the pulse-echo ultrasonic technique, an ultrasound wave is excited and detected by two identical piezoelectric transducers (transmitter and receiver), which are glued to polished opposite sides of a sample. The time evolution of the amplitude of the received pulse is defined by the sound attenuation.

Echo sounding is a type of sonar used to determine the depth of water by transmitting acoustic waves into water. The time interval between emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time.

The fundamental difference between these two methods is that the transmission method uses two transducers and gives a measurement of signal attenuation, while the pulse-echo method uses a single transducer that can measure both transit time (distance) and signal amplitude, and hence the attenuation together with other …

The second key principle is the pulse-echo principle, which explains how the image is generated. Ultrasound waves are produced in pulses, not continuously, because the same crystals are used to generate and receive sound waves, and they cannot do both at the same time.

The ultrasound image is produced based on the reflection of the waves off of the body structures. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide the information necessary to produce an image.

In an ultrasound exam, a transducer both sends the sound waves and records the echoing waves. When the transducer is pressed against the skin, it sends small pulses of inaudible, high-frequency sound waves into the body.

Explanation: When an alternating magnetic field is applied to a ferromagnetic material, then the rod is thrown into vibrations, thereby producing ultrasonic waves at resonance. Therefore ultrasonic waves can be produced using magnetostriction effect.

Magnetostriction Oscillators are mechanically rugged. The construction cost is low. They are capable of producing large acoustical power with fairly good efficiency. It can produce frequencies up to 3MHz only.

: an electric oscillator in which the frequency is controlled by the mechanical vibrations induced in a body by magnetostriction.

Magnetostriction is a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. The effect was first identified in 1842 by James Joule when observing a sample of nickel. This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.

The degree of magnetostriction can be measured by the magnetostrictive coefficient λ, which is the ratio of the fractional change in length (also known as strain or the change in length divided by the original length) to the magnetization of the material.

Matteucci Effect: When a magnetostrictive material is subjected to a torque, a helical anisotropy of the susceptibility of that material will be created. Wiedemann Effect: When a helical magnetic field is applied to a material, it results in twisting of that material (reverse of Matteucci effect).

Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials’ magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ.