Electro-Magnetic Acoustic Transducer (EMAT) tackles corrosion and isolated pitting unlike other advanced techniques.
Electro-Magnetic Acoustic Transducer (EMAT) offers a reliable solution to detecting corrosion and isolated pitting screening in difficult to access areas. Established through decades of research and development, many industries have adopted EMAT testing as an effective and accurate non-destructive testing method in metal manufacturing and processing, automotive, railroad, pipeline, boiler and pressure vessel equipment.
EMAT is a dry coupled ultrasonic non-contact technique that is based around the use of electro-magnetic energy to generate ultrasonic sound wave in the component being tested. Due to this couplant-free feature, EMATs are particularly useful in harsh environments - think hot or cold.
The EMAT generates an ultrasonic pulse within a metallic and/ or ferromagnetic test object. The sound waves are generated in the material and thus no couplant is needed. Consisting of a magnet and an electrical coil, the EMAT uses electro-magnetic forces to introduce sound energy into the test object through a combination of Lorentz Force and Magnetostriction.
Applications of EMAT
- Dry coupled thickness measurement.
- Possible to inspect temperatures up to 200˚C.
- Corrosion under supports using MRUT-A mode.
- Flaw detection in steel products.
- Detection of pinhole like defects.
- Plate lamination defect inspection.
- Pipeline in-service inspection and direct assessment of partially excavated piping.
- Scanning of piping low to the ground and resting on the ground.
Advantages of EMAT
- EMATs use a non-contact testing method.
- EMATs do not require couplant for transmitting sound.
- EMATs can inspect through thin coatings and are not affected by minor surface roughness.
- EMATs offer easy probe deployment – not having wedges or couplant, Snell’s Law of Refraction does not apply and the angle of the probe does not affect the direction of propagation. This makes the probes easier to deploy.
- EMATs can screen for corrosion from unlagged locations up to 3m each way (6m in total per scan).
- EMATs can scan piping to detect corrosion at the Air to Ground Interface (AGI’s).
Corrosion Under Support
Commonly applied in the oil, gas and power industries, EMAT is used to detect the prevalent problem of corrosion under pipe supports. This touch point corrosion occurs at the point where pipelines rest on pipeline supports. The touch point location creates the ideal environment for corrosion to form as moisture gathers under the pipeline at the area where the pipeline material meets the pipeline support.
Traditionally, inspecting these areas for touch point corrosion has been a challenge as the inspection method of lifting the pipeline to inspect the area underneath poses a host of challenges.
EMAT is a rapid scanning technique that essentially sends a signal circumferentially from the 12 o’clock position around the pipeline to inspect the 6 o’clock position, which is where the touch point corrosion occurs. Due to the placement of the sensors on the top of the pipeline there are restrictions as to what types of pipeline supports can or cannot be inspected.
Detection of Pinhole Type Corrosion
Detecting pinhole type corrosion in pipelines or other industrial assets has always been challenging due to the shape of the corrosion and its interaction with the signal produced by common inspection techniques, such as Ultrasonic testing. With such techniques, locating pinhole type corrosion may present overly time consuming or, in some cases, the technique is not well suited to detect them at all. This is mainly due to ultrasonic beam spread as well as the non-reflective nature of the pit geometry making it very easy to miss significant pitting.
Due to the signal generated by EMAT it is unlikely to miss these defects due to the very high Probability of Detection (POD) of the method. Whilst other techniques can detect pinhole type corrosion, it is the rapid scanning method used by EMAT that increases its suitability on a practical level. This method is particularly useful in the detection of corrosion types typically associated with microbiologically influenced corrosion (MIC).
The ALS Approach
ALS continuously looks ahead and regularly invests in the latest technologies available to our industry. With continual advancement and superior customer value a priority, ALS is able to continually deliver the most advanced, efficient and effective inspection methods available in the asset care field.
Technologies such as EMAT, which supplement our existing inspection expertise, are embraced by ALS only after successful method validation, technician training and certifications. This ensures a solid understanding of exactly where and how these technologies should be applied, and ensures all ALS inspectors are confident they will produce accurate results.