An article that was published on the October issues of POWER magazine
Acoustic pulse reflectometry (APR) is a tube inspection method that has been gradually gaining acceptance as a tool for heat exchanger inspection. Different types of heat exchangers operating in different operating environments have different failure mechanisms, making some of them more suited than others for inspection by APR. Finned tube heat exchangers are a typical example of heat exchangers particularly conducive to APR inspection.
The reason APR is particularly useful on finned tube heat exchangers is that it is purely an internal pipe inspection method. This is a limitation where tubes are susceptible to external damage by corrosion or abrasion from support plates. In finned tube exchangers, however, the tubes often rest on top of each other, supported by the fins. There are no support plates, and in cases where the external fluid is forced air, there are no hostile chemicals on the exterior of the tubes.
Dual-cycle geothermal power plants often employ this type of heat exchangers. In this type of geothermal plant, hot brine heats an organic liquid having a low boiling temperature, turning it into vapor. This higher-pressure gas expands through the turbine, producing power. The lower-pressure gas is then condensed using finned tube heat exchangers (condensers in this case), which are cooled by air forced across the highly finned heat exchanger tubes by large fans. Thoroughly inspecting these heat exchanger pipes has been problematic, until now.
To read more, please click on the following link: http://www.powermag.com/issues/departments/focus_on_o_and_m/Applying-Acoustic-Pulse-Reflectometry-in-a-Geothermal-Plant_4032.html