DMTA-10043-01EN, Rev. C, July 2016Chapter 106610.3 High Temperature MeasurementsCorrosion measurements at elevated temperatures require special consideration.Keep in mind the following points:• Be sure that the surface temperature of the test piece does not exceed themaximum specified temperature for the transducer and couplant that you areusing. Some duals are designed for room temperature measurements only.• Use a couplant rated for the temperature where you will be working. All hightemperature couplants will boil off at some temperature, leaving a hard residuethat is not able to transmit sound energy. Olympus Couplant (H-2) can be used attemperatures up to 398 °C (750 °F), although it will boil as the upper limit isreached.Maximum recommended temperatures for Olympus couplants are provided inTable 7 on page 66.Not all types of couplant are available in every country due to local regulation.Consult your local Olympus representative for a list of available couplants.• Make measurements quickly and allow the transducer body to cool betweenreadings. High temperature duals have delay lines made of thermally tolerantmaterial, but with continuous exposure to very high temperatures the inside ofthe probe will heat to a point where the transducer will be permanently damaged.Table 7 Couplant selectionCouplant TypeMaximumrecommendedtemperatureB Glycerine 90 °C (200 °F)D Gel 90 °C (200 °F)H-2 HighTemperatureUp to 398 °C (750 °F)