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Plate Structure Inspection and Monitoring

MsS system can be used to inspect and monitor following plate structures:
  • Ships
  • Airplanes
  • Above or underground storage tanks
  • Containment liners in nuclear power plants
  • Steel bridges
  • Steel columns in high risers
  • Pressure vessels
  • Pipe having a diameter higher than 60 inches
The principal defect developed in these structures in service is loss of material wall thickness by corrosion and cracking. Corrosion may be localized or present over large areas. Cracking may occur at high stress concentration areas and at weld joint.

The MsS plate probe consists of a thin strip of ferromagnetic material and a coil in a thin printed circuit board placed over the strip as shown in the below figure. The probe contains two coils for control of wave propagation direction and has been made of ferromagnetic strip in thicknesses ranging typically from 0.05 to 0.25 mm.

The ferromagnetic strip is attached to the structure under testing by using an adhesive—for example, epoxy. The MsS plate probe based on the ferromagnetic strip is low profile, lightweight, surface-mounted, durable, and relatively inexpensive, and therefore has high potential for practical monitoring use.

As an example of guided wave monitoring with MsS system, a defect growth monitoring was performed in a test sample of 6.45 mm thick and 1.22 m x 12.19 m in overall size. A 20-cm-long, thin-strip MsS probe was adhesively bonded to the test sample approximately 3.66 m from the closer end. Corrosion defects were made with 6.35-mm-diameter, 50%-thickness-deep drilled hole at 7 meter from the MsS probe. The photo shows the 6.35-mm-diameter, 50%-thicknes-deep drilled holes.

The data show a series of subtracted data that were obtained by subtracting the baseline data (data acquired after installation of MsS plate probe) from the periodically acquired data: the first trace is subtracted data by subtracting the baseline data from the data acquired before making defect, the 2nd, 3rd, and 4th traces are subtracted data of periodically acquired data with one, three, and five drilled holes, respectively. As can be seen in the plot, the drilled-hole signal was readily detectable when the number of drilled hole was three or more despite of the facts that the defects were 7 meter away from the sensor location and small in size. This result clearly demonstrated the ability of the MsS probe to inspect and monitor a large area of plate structure for detection of defects and their growth.

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