INVESTIGATION OF FATIGUE AND CREEP DAMAGE IN STEAM BAILER PIPES BY ULTRASONIC TESTING

In this paper, the initial results of the research on detection of fat igue and creep damage in steam boiler pipes of a thermal power plant a re presented. An ultrasonic method was preferred since construction, o rientation of the damage, geometry and surface condition of the pipe l imit the use of other non-destructive testing methods. In order to det ermine the relative sizes of fatigue cracks, comparison notches were d rawn by using the echoes from comparison notches having different open ing angles and depths. For a better optimisation of ultrasonic echoes, a miniature probe (4 MHz-70 degrees) was modified by mounting a wedge which has the same surface curvature as the pipes. The voids formed d ue to creep were detected by measuring the variation of ultrasonic wav e velocities in the material using a TR probe.