EMAT as Acoustic Emission Transducer

Some oil companies inspect their tubular and vessels periodically based on their experience. Others prefer of inspecting the one which is having problems.  The problems related to material qualities vary such as cracks, pittings, corrosions, and discontinuities. Solid depositions are often found in the flowline, tubing, and vessels. An inspection company or pipeline inspection companies such as Tuboscope (http://www.tuboscopevetco-egy.com/) has many methods for inspecting tubular and vessels including by using an electromagnetic transducer.

Generally, tubular and vessel inspection is required mostly for safety purposes. A public oil company spends thousands of dollars to maintain their reputation. The operation department allocates budget for inspection by ndt companies to decrease downtime. Some wells with excessive water production are inspected for casing failure. Geothermal well casings are inspected for corrosion failures due to H2S and high-temperature fatigue.

The inspection company uses many methods to survey the objects. A practical method is applying the ultrasonic wave to materials being tested. An acoustic emission transducer equipped with electromagnetic acoustic transducer or EMAT is a popular tool in oil field inspection. Research activities in this field are ongoing to decrease the negative effect of noise during testing.

Technically, the pattern of ultrasonic waves between generator and receiver can be evaluated to determine the quality of the material being tested. Magnetic field and eddy current will generate Lorentz forces and if paired with a conductive material such as steel, the forces will excite acoustic waves through the material. By controlling the AC electric frequencies between 20 kHz and 10 MHz, the sound wave is in the range of ultrasonic sound which is useful to identify the quality of materials. The main difference of EMAT with other acoustic transducers is the use of a couplant. EMAT or electroacoustic transducer does not require couplants during testing in which is very beneficial in a high-temperature environment. However, the noise sometimes generates difficulties during analysis.

In the present invention, the inventor introduces better Electromagnetic Acoustic Transducer (EMAT).  The transducer has a core with a permanent magnet.  The permanent magnet polarity is changed for switching thereby noise can be eliminated.

Alternating current through electric winding on the core builds the magnetic field. As explained above, together with a coil which is induced eddy current will create Lorentz forces that acoustically excite the object.  Recorded acoustical wave between transmitter and receiver is analyzed to determine the quality of the object.

Recommended reading, a tool to demonstrate eddy current, and piezo transducer for acoustic guitar:

Author: admin

The Admin is a professional in the oil and gas field operation and management. He has a degree in petroleum engineering and he is also a certified Intellectual Property consultant. He has more than 20 years of experience at various levels of his carrier. He has published more than 40 articles related to his professional experiences.

3 thoughts on “EMAT as Acoustic Emission Transducer

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