Re: Magnetization principle transducer In Reply to S.Mohamed Riaz at 15:39 May-06-2009 (Opening).
Magnetostrictive Sensor (MsS) probe uses magnetostrictive principle (mechanical deformation of ferromagnetic material when magnetic field is applied) for generating and receiving ultrasonic wave. The magnetomechanical coupling constant of ferromagnetic material (compared to electromechanical coupling constant in piezoelectric material) is high at low frequency usually lower than 500 kHz. The ultrasonic wave using magnetostrictive principle is used at low-frequency application such as SONAR (sound navigation and ranging) in underwater, massager using ferrite, or MsS probe for long-range ultrasonic testing (LRUT).
MsS probe used for long-range ultrasonic testing (LRUT) in Petrochemical Industry has much merit compared to transducer belt using piezoelectric transducer as follows:
1) MsS probe covers the whole circumference of pipe compared to discrete coverage of pipe circumference with piezoelectric transducer belt. We use torsional or longitudinal wave for LRUT of pipeline. We have to use continuous probe covering 360 degree of pipe circumference because both torsional or longitudinal modes are axial symmetric wave.
2) The guided wave signal generated with MsS probe has better signal-to-noise ratio than that generated with piezoelectric transducer belt because much less generation of flexural wave mode. The piezoelectric transducer belt uses ultrasonic probes located discretely along the circumference of pipe, and it naturally generates flexural wave mode that increases background noise level.
3) The MsS probe generates much stronger guided-wave signal because its probe has more coverage around the circumference of pipe, good impedance matching between steel and ferromagnetic strip, and strong magnetomechanical coupling constant operating at low frequency.
4) The dead zone length and near-field length of MsS probe are much shorter than that with piezoelectric transducer ring. Because MsS probe that covers 360 degree of pipe does not have near-field zone. Therefore, the sum of dead zone length and near field length is about 0.4 ft with 128 kHz, 0.7 ft with 64-kHz, and 1 ft with 32-kHz center frequency on each side of the MsS probe. The near-field length with piezoelectric transducer ring is about 1.5 m (4.9 ft) on each side of the ring (Reference: Guided Wave Testing of an Immersed Gas Pipeline, Material Evaluation/February 2009, page 106).
5) The MsS probe has better direction control compared to discrete piezoelectric transducer belt because it uses axial symmetric probe.
6) Inspecting pipe size: 1/8-inch to 60-inch-OD pipe, pressure vessel bigger than 40-inch-OD using sectional probe
7) Clearance along the length of pipe, that is required for installing probe, is about 2.5 inches.
8) It allows guided wave data of wide-frequency band covering between 5 and 250 kHz. The MsS probe operates usually 1 or 2 cycles of tone-burst electric pulse, it can give you wide band guided-wave data at each center frequency. MsS guided-wave probes operate at different center frequency such as 16 kHz or lower frequency, 32 kHz, 45 kHz, 64 kHz, 90 kHz, 128 kHz, 180 kHz, and 250 kHz.
9) High temperature inspection for a pipe: less than 150 Celsius degree for inspection and 300 Celsius degree for monitoring (once the probe is bonded).
10) Allow installing probe if the pipe circumference of 70 percent or more is accessible. It allows guided-wave inspection without removing heat-tracer line.
11) Application with MsS system is almost the same as that of any system using piezoelectric transducer because the guided wave system is only generating and detecting guided wave in pipeline (or structure). The wave propagation in pipe and its interaction with defect or geometric feature does not change.
12) Inexpensive monitoring probe that can be permanently installed in pipe
For more information about long-range guided-wave system, please visit the following website (http://www.gwanalysis.com/) or email me at email@example.com.