The Importance of Magnetic and Ultrasonic Testing for Industries

Various techniques used in Non Destructive Testing or NDT in the industry include visual and radiography, ultrasonic testing, and eddy current or magnetic testing. Depending on the industry, different services are used in the magnetic testing field. Therefore, in the pipeline sector the use is made of the Magnetic Flux Leakage or MFL as well as the Portable Yoke. The MFL method utilizes the principle of generation of flux lines around the steel pipeline by using a powerful magnetic field. Corrosion is detected as well as pitting in storage tanks or pipelines or other steel structures by estimating the missing areas of flux lines. In an advanced version of the MFL method of magnetic testing, an inline tool is used that both cleans and scans the wall of the pipeline as it travels through it.

Ultrasonic testing methods are used in the industry to measure the build-up of oxide and the thickness of samples besides monitoring of corrosion. Electromagnetic Acoustic Transmission or EMAT, PA or Phased Array, and TOFD (Time of Flight Diffraction) are some of the services that are used. The TOFD method is normally used for the accurate estimation of cracks in welded joints. In this, a set of probes is mounted on a buggy that travels along the welded section while inspecting and transmitting the recordings. The PA method uses a principle by which a high-resolution beam reveals the internal image of the object. Acoustic Ranger, Automated Ultrasonic Testing or AUT are some of the other methods under this form of testing.

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An Overview of the Methods of Nondestructive Testing

Nondestructive testing methods are periodically used by the industry as a means of ensuring the health of all the individual units comprising it. Thus, pipelines are regularly cleaned and tested for cracks. Turbines are similarly periodically checked for cracks and imperfections in either the blades or in the turbine itself. Units, due to being subjected to a combination of high temperature and stresses or high thermal stresses, also need to be checked using the appropriate tool in nondestructive testing. These tools and corresponding procedures include, are Eddy Current, Dye Penetrative agent, Radiography, Ultrasonic Testing and Magnetic Testing.

The Ultrasonic Testing applications include the measurement of thickness, the monitoring of corrosion as well as the build up of oxides, near drum boiler tools, and hydrogen induced cracking among others. The techniques used include the Acoustic Ranger, Advanced Flaw Sizing, EMAT or electromagnetic acoustic transmission, TOFD or time of flight diffraction and PA or Phased Array. In the TOFD method, a set of probes is used for the accurate estimation of cracks in welds. The probes are mounted on a buggy that travels along the weld being inspected. The data generated during travel is analyzed to reveal cracks.

Magnetic Testing methods are used for the examination of turbine blades, welds and pipelines. The Alternating Current Field Measurement (ACFM), Magnetic Flux Leakage (MFL) and the Portable Yoke are some of the methods in use. The ACFM can be used for metals, non-metals and their alloys and through coatings as well. The MFL is used for steel structures only.

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