Development of Magnetostrictive Sensor for Plate Inspection, 15-9077

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Principal Investigators
Hegeon Kwun
Sang Young Kim

Inclusive Dates: 04/01/98 - 04/01/00

Background - Because of the increasingly competitive business environment, industries are looking for methods of reducing operating costs. Industries such as gas, oil, petrochemical, chemical, and electric power operate and use large equipment or structures that require a high capital investment. The maintenance expense for these structures constitutes a large part of the overall operating cost. To reduce maintenance costs without compromising operational safety, industries have been searching for better and more efficient ways to inspect their equipment and structures.

In answer to industry's search for cost-effective inspection methods, the Institute has developed and patented a nondestructive evaluation (NDE) technology called the magnetostrictive sensor (MsS). The MsS is a device that electromagnetically generates and detects elastic-guided waves in a ferromagnetic material such as carbon steel. With the MsS® technology, elastic guided waves in sonic or ultrasonic frequencies are generated and propagated in a structure under inspection. Waves reflected from structure defects are detected, typically, by using the pulse-echo method. The occurrence time of a defect signal (from the time of initial pulse) and the signal amplitude are then used to determine the severity and location (from the sensor position) of the defect. The elastic guided waves can propagate more than 100 feet in typical plant piping and, thus, can be used to probe a long section of a structure quickly. In addition, the MsS, being an electromagnetic sensor, can be applied without direct physical contact to the surface of the part under inspection (for example, over coating or painting on the pipe) and, therefore, can be applied with minimum supporting activities. With the guided wave's long-range probing capability and the MsS's noncontact sensing capability, the MsS technology provides a very cost-effective method of inspecting large structures globally.

Application of the MsS technology to piping and tubing inspection has been successful, and the commercialization of the technology for this application has begun. In addition to tubular structures, the industries also need cost-effective NDE methods for plate-like structures such as aboveground storage tanks and steel liners in nuclear power plant containments. This project is designed to extend the MsS applicability to the inspection of plate-like structures. It was motivated to meet the industrial needs and to secure and maintain the Institute's technical initiative and worldwide leadership in the development of this technology.

Approach - The MsS used for piping or tubing inspection employs coils that encircle the structure. For plates, the accessibility is limited to only one side of the structure and, consequently, the encircling coil-type MsS cannot be used. Instead, an MsS probe will be developed that uses a coil wound around a U-shaped core and is electromagnetically coupled to the plate under inspection. The development of the MsS probe for plate inspection will be accomplished through a systematic approach that includes the design and evaluation of preliminary MsS probe designs, prototyping, and capability demonstration on laboratory plate samples.

Accomplishments - Prototype MsS probes were designed and fabricated. Using these probes, guided plate waves of symmetric and asymmetric longitudinal Lamb wave modes and shear horizontal wave mode were successfully generated and detected in a 0.5-inch X 4-feet X 20-feet carbon steel plate. The capability for long-range, global inspection of plate was also demonstrated by placing artificial defects in the carbon steel plate samples and detecting them using the MsS technique.

For more information, please contact Glenn M. Light, Ph.D.

      Measurement & Nondestructive Evaluation of Materials & Structures Program
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