EMAT BOILER TUBE INSPECTION
EMAT technology is an Ultrasonic Non Destructive Testing method that differs from traditional ultrasonics in the way the sound is generated. In conventional ultrasound technology a piezoelectric crystal is used to convert electrical energy into mechanical vibration. The vibration makes its way into the test piece via the couplant. EMAT consists of a magnet and a coil of wire and relies on electro-magnetic acoustic interaction for elastic wave generation.
Using Lorentz forces and magnetostriction, the EMAT and metal test surface interact and generate an acoustic wave within the material. The material being inspected is its own transducer, eliminating the need for liquid couplant.As no couplant is required it is much easier to do continuous scanning rather than spot checks as it normally the case with ultrasonics.
The EMAT system is relatively insensitive to surface roughness due to the principle of operation.With ultrasonics it is normally not possible to test through scale due to absorption and scattering of the beam. In the case of EMAT it is possible to test through moderate scale deposits, although very thick scale deposits can still prove troublesome.
Advantages of EMAT as against thickness testing:A continuous scan is achieved rather than spot checking so that the integrity of the inspection is significantly improved. Normally there is no need for either surface preparation negating the time and cost of such operations.Results easily viewed on a 3D model. Data trending can be carried out from follow up inspections.