ELECTROMAGNETIC-ACOUSTIC TRANSDUCERS FOR IN-SERVICE MANUAL TESTING OF HEATED OBJECTS

摘要

The problems of Ultrasonic Testing (UT) of metal products and constructions with the surface being heated up to 300-800C are considered. It is noted that the process of UT of objects at chemical plants of heat-power, metallurgy industry etc complicates the need to protect Ultrasonic transducers from heated surfaces, hot air and heat radiation from objects, with the operational conditions becoming dangerous. We offer to use electromagnetic-acoustic (EMA) excitation and signal reception technique that does not require direct mechanical contact of the transducer with a heated surface of the object under test. The EMA transducers (EMAT) are protected from thermal influence by a thin shield made of heat-resisting material with low thermal conductivity; they do not require the use of couplants and are intended to be used as a part of a serial EMA gauge A1270 for testing of products heated up to 3000C with no additional heat-shielding. The designed time mode follows the scheme. This enables the transducer to work reliably for 8 hours. Such a successful design of the EMAT and the use of a composite protector made of alumina ceramics provide reliable test parameters. The same EMAT can be used to test objects heated up to 7000C. There is a developed carrying-in and -out system for the EMAT. The system is provided with a heat-resisting shield that protects the EMAT from thermal influence of the object under test and significantly reduces the influence of it onto an operator. The designed time modes for testing of objects at different temperatures prevents the operating part of the EMAT from overheating and, at the same time provides multiple measurement of heated object thickness. Also there is compensation of the thermal influence from an object onto the US wave velocity.