Development of Torsional Wave Mode Probe for Heat Exchanger Tube Inspection, 14-9404

Principal Investigators
Hegeon Kwun
James F. Crane

Inclusive Dates:  07/01/03 - Current

Background - Heat exchangers are key equipment in processing plants such as refineries, chemical plants, and electric generation plants. To enhance heat exchanger (HX) reliability, a cost-effective and comprehensive inspection method and tool are needed. A long-range guided-wave inspection method such as SwRI's magnetostrictive sensor (MsS^®) technology can quickly inspect a long length of piping (typically, more than 100 feet) from a fixed probe location. This method has long been recognized as a potential ideal solution for quickly surveying HX tubes. Advantages include inspection of the whole tube length from one end, cleaning needed for only the probe placement area, and short inspection time.

Approach - The probe design approach is based on the torsional (T)-mode MsS and the tube gun concept (both patented by SwRI). The T-mode is dispersion-free and less prone to generation of extraneous wave modes and, thus, produces higher quality data than the L-mode. Also, the T-mode MsS that uses a ferromagnetic strip is simple and has high conversion efficiency. The approach involves generating and detecting
T-mode waves on a cylindrical waveguide, inserting the end of the waveguide in the tube undergoing inspection, mechanically expanding the end of the waveguide to make intimate contact with the inside surface of tube, and coupling the T-mode waves to the tube and vice versa.

Accomplishments - The developed T-mode HX probe is illustrated below left. Performance evaluations in the laboratory and on HX mockups at an outside laboratory showed that the probe exceeded the target of detecting 5-percent defects within 40 feet. Examples of data obtained from a 20-foot-long U-bend tube using the developed probe are also given below right. A patent application for the T-mode HX probe has been filed.

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