(b) Flaw detection As in high temperature thickness gaging applications, high temperature flaw detection most commonly uses dual element or delay line transducers. All standard Panametrics-NDT flaw detection duals offer high temperature capability. Fingertip, Flush Case, and Extended Range duals whose frequency is 5 MHz.Conventional ultrasonic transducers will tolerate temperatures up to approximately 50 C or 125 F. At higher temperatures, they will eventually suffer permanent damage due to internal disbonding caused by thermal expansion. If the material being tested is hotter than approximately 50 C or 125 F.Although the delay line insulates the interior of the transducer, lengthy contact with very hot surfaces will cause significant heat buildup, and eventually permanent damage to the transducer if the interior temperature becomes hot enough.Custom transducer setups will be required. Standard delay lines for this family of transducers can be used in contact with surfaces as hot as 480 C or 900 F. For a full list of transducers and delay lines, see this link: Replaceable Face Transducers.Many users have found the best technique to be to apply a drop of couplant to the face of the transducer and then press the transducer firmly to the test surface, without twisting or grinding it (which can cause transducer wear).