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Inspection Trends - January 2011 - Winter

Inspection Trends / Winter 2011 25 technologies enter the market that enable 100% inspection of tubes easier and faster than previously possible, organizations can begin to put an end to sampling to ensure the safety and efficiency of their critical systems. Acoustic Pulse Reflectometry An acoustic-based technology is enabling companies to accurately and rapidly perform comprehensive inspections, drastically reducing the chance of catastrophic failures. Acoustic pulse reflectometry (APR), the technology found in the AcousticEye Dolphin™ tube inspection system (Fig. 1), offers speed, accuracy, and objective testing results. Acoustic pulse reflectometry inspects pipes and tubes from the inside and is independent of tube material or configuration. It is noninvasive and the report generated is objective and independent of a highly trained professional; therefore, the entire inspection procedure can be up to ten times faster than other methods. The core technology of APR encompasses an acoustic pulse traveling down the air enclosed in the tube — Fig. 2. As long as the pulse does not encounter any changes in the tube cross section, the pulse continues to propagate, with some attenuation due mainly to friction between the molecules of air and the tube wall. If, however, any discontinuity is encountered, reflected waves are created, which propagate back up the tube. The more abrupt the changes in the cross section, the stronger these reflections are. Software records and analyzes the reflections to determine what kind of discontinuity caused them. Discontinuities diagnosed include holes, pits, general wall loss, and bulges. By identifying these types of faults before problems arise, organizations can prevent costly failures down the road. Real-World Applications Acoustic pulse reflectometry is being successfully used in the inspection of heat exchangers. Essentially, heat exchangers are devices used to transfer heat from one fluid to another. Most commonly, heat exchangers are constructed of hundreds to thousands of tubes in parallel, encased in a metal shell. In general, heat exchangers are found in a large variety of industries such as power plants; refineries; paper mills; heating, ventilation, and air-conditioning; food and beverage; chemicals; and many more. Operating around the clock over long periods, heat exchangers are subject to eventual degradation or failure through many mechanisms: erosion, corrosion, abrasion (caused by support plates rubbing against the tubes), thermal shock, sedimentation, fouling, etc. Plant operators are aware of these inevitable issues and aim to inspect their heat exchangers periodically, both to ensure their efficiency and to prevent catastrophic failures, which can be very costly. Acoustic pulse reflectometry is helping plant operators to easily and quickly perform these important inspections, minimizing downtime for their facilities. Acoustic pulse reflectometry is also a valuable tool in the assessment of internal cleanliness of heat exchanger tubes. Tubes are routinely cleaned during plant turnaround periods to remove any deposits hampering their functionality; however, the traditional technologies used for this are slow. In an APR inspection, tubes that were not properly cleaned will demonstrate multiple reflections from the constriction caused by such deposits, providing a rapid and cost-effective means for assessment of tube cleanliness as the inspection is carried out. Additionally, APR has been applied to inspection of reactors in chemical plants. Reactors are similar to heat exchangers, though they operate at elevated temperature and pressure levels, causing failures in the form of both bulges and collapse of tubes. Both types of faults present a great challenge to traditional testing methods, but with the noninvasive nature of APR, complete testing of these systems is possible. Fig. 1 — The Dolphin™ system from AcousticEye performs quick, nondestructive inspections of tubes and pipes. The system inspects tubes made of any material and in any configuration. Fig. 2 — The acoustic pulse reflectometry system in use. It can detect such discontinuities as holes, pits, wall loss, and bulges.


Inspection Trends - January 2011 - Winter
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