Methods and devices for inspecting waterwall tubes for the detection of
fire side damage over a long length of the tube are described. The system
of the invention uses a magnetostrictive strip and a flat coil-type plate
magnetostrictive sensor (MsS) that are held in place on the waterwall
using a specially designed frame and an electromagnetic circuit. The
magnetostrictive strip and plate type MsS are positioned against a tube
in the waterwall using an elastomeric pad or a fluid filled bladder to
achieve close contact and good mechanical coupling between the
magnetostrictive strip and the tube surface. When current activated, the
electromagnet holds the entire assembly in place and provides a DC bias
magnetic field required for plate magnetostrictive sensor probe
operation. Long-range guided-waves are pulsed into the tube and reflected
signals are detected within the same sensor structure. The received
signal data representative of a long section of the tube under
investigation is then analyzed for the presence of anomalies and defects.
When data acquisition for a particular tube or tube section is completed
the electromagnet is turned off and the entire device is moved to the
next tube in the waterwall.