Inspecting U-Tube Bundles Using Acoustic Pulse Reflectometry

Abstract

Acoustic Pulse Reflectometry (APR) has recently been gaining acceptance for a variety of tube inspection applications, as a viable alternative to more entrenched technologies such as eddy current. In this paper we present a case study demonstrating how APR can be used successfully for inspecting U-tube bundles. This type of heat exchanger poses a great challenge to technologies which require traversal with a probe, due to the presence of tight bends in the tubes. These are usually not traversable by probes. APR, on the other hand, uses an acoustic pulse as a “virtual probe”, with the ability to navigate bends, elbows, fittings etc. with no difficulty. In this paper we show how the various typical faults are revealed in the acoustic measurements and demonstrate how the analysis software recognizes these faults and generates the report. In one case presented here we inspected 62 heat exchangers used to heat natural gas, containing 39 U-tubes each, totaling 2379 tubes. Each tube had an internal diameter of 11mm, wall thickness of 2.5mm, and a length of approximately 6 meters, though there was some variability in length due to different lengths of the U bends. An added difficulty in inspecting these tubes was that the tube sheet was about 80 centimeters in distance from the inspection port-hole. The average inspection time in the field was 25 seconds per tube. All measurements were logged to computer files, and automated fault detection software generated a full report showing the condition of the tubes, indicating degradations in wall thickness, full and partial blockages, and holes. In the second case study we examine the variability in u-tubes in a single bundle and discuss the effect this has on the results.

Twin-tube practical acoustic thermometry: theory and measurements up to 1000 °C

“…In order to fully describe the way sound propagates through the tubes of a PAT device, it is important to consider the effects of bends in the tubes, and reflections from both the tube ends and the microphone and speaker ports. Such acoustic perturbations can be detected by acoustic pulse reflectometry [11][12][13][14] which uses similar techniques to those described here, but by assuming the temperature is known, they use the information instead to detect partial blockages in boiler tubes. They report that smooth bends give rise to reflections at the junctions with straight regions, probably arising from small changes in cross-sectional area arising from the bending process.…”

New methods of technical diagnosis of pipelines

“…The screening diagnosis system does not have this demerit because pipes with diameters ranging from 10 to 165 mm can be investigated with the aid of one transducer. The Dolfin system was developed by the Dutch company AcousticEye [3][4][5][6].…”