In this paper, the initial results of the research on detection of fatigue and creep damage in steam boiler pipes of a thermal power plant are presented. An ultrasonic method was preferred since construction, orientation of the damage, geometry and surface condition of the pipe limit the use of other non-destructive testing methods. In order to determine the relative sizes of fatigue cracks, comparison notches were drawn by using the echoes from comparison notches having different opening 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 due to creep were detected by measuring the variation of ultrasonic wave velocities in the material using a TR probe.