Ultrasonic study for flaw detectability in ferritic butt welds at high temperatures

This paper describes the problems encountered during ultrasonic testing of welds at high temperatures, the overall assessment of sound propagation at high temperatures and an innovative technique to circumvent the problems using the conventional probes. In the absence of high-temperature transducers an attempt has been made by the authors to examine welds in the high temperature zone up to 300°C by using contact angle beam probes (less than 4 MHz) and scanning from the region (beyond 5^th Vee path) at room temperature. The experimental study involved the creation of natural defects such as cracks, incomplete penetration, porosity etc., in the ferritic butt weld (16 mm thickness) at predetermined locations. The comparative study was carried out between the responses obtained from the defects at ambient temperature and elevated temperatures. The analysis of the results have shown that the attenuation of ultrasound increases as the temperature at the weld zone increases. It can be seen from the results of the experiments that by making attenuation corrections it is possible to inspect the welds below 300°C without substantial performance loss at test frequencies less than 4 MHz.