A method and system for implementing magnetostrictive sensor techniques
for the nondestructive evaluation of pipeline structures. The system
consists of a magnetostrictive sensor instrument unit, a data storage
unit, and a plurality of magnetostrictive sensor probes are positioned on
an in-line inspection vehicle. The instrumentation unit includes
electronics for transmitting excitation pulses to a transmitting
magnetostrictive sensor probe as well as electronics for amplifying and
conditioning the signals detected by a receiving magnetostrictive sensor
probe. The magnetostrictive sensor probes include both plate
magnetostrictive sensors and permanent magnets which provide a DC bias
magnetic field necessary for magnetostrictive sensor operation. The
transmitting and receiving probes are attached to the in-line inspection
vehicle by way of mechanical arms on opposing sides of the vehicle. The
mechanical arms are spring loaded and are equipped with rollers which
maintain the probes at approximately constant distances from the inside
diameter of the pipe wall. The method involves generating pulses of shear
horizontal waves of frequencies less than 200 kHz. The transmitting
magnetostrictive sensor probe generates a wave that propagates in both
directions around the circumference of the pipe wall from a point
adjacent to the transmitting probe. Both waves are thereafter received at
the receiving probe spaced 180 degrees apart from the transmitting probe.
Any defect present in the pipe wall within the circumference being
investigated will show up in the received signal.