We have carried out a statistical analysis of the surface roughness and waviness for standard products tested to Russian GOST and for calibration blocks used for ultrasonic flaw detector sensitivity calibration. An analysis showed that in fact:

• as a rule, surface treatment quality of products to be tested is worse than that of calibration blocks, and worse than Rz40 mkm by requirement of GOST14782-86;
• failure to take into account this fact results in uncontrolled decreasing the flaw detector actual sensitivity level that may reach 5-23dB (by our experiments) and depends on type of transducer.

The thickness of the contact layer R_max on coarse surface irregularities and one is more than in specimens with regular surface. It has been carried out special experiments by assessment of correlation between roughness and amplitude of ultrasonic signal and between R_max and R₂. Results are shown necessary to measure of roughness in unit of R_max; between R_max and R₂ is the correlation tie, which depends on the kind of the surface profile autocorrelation function. The ties between autocorrelation functions of surface roughness profile and signal amplitude fluctuation of various probes were set. It was proposed the quantitative instrumental criterion to characterise surface unevenness. Conventional instruments (like SURTONIX 10) cannot be used for measuring on rude statistically rough surface, because its measuring base is sufficiently smaller than ultrasonic beam size.

Principally new method of surface roughness and waviness measurement by the same ultrasonic flaw detector was developed by author. The method does not involve an ultrasound introduction into metal and is realized by special probe (SRC - technique). The SRC-probe forms additional pulse with time delay from initial pulse and its amplitude depends on surface roughness only but is not affected by the presence of liquid on surface, product configuration material structure, etc. There is good correlation between the additional pulse amplitude and the roughness height parameter and by other side the transmission coefficient through the contact layer. There are special nomograms.

The developed SRC-technique was included in manual operations and it is obligatory for application during ultrasonic testing of nuclear power plants equipment in Russia. This substantially increases of reproducibility of results of testing.

SRC-technique is very important for the monitoring for development of defects in operating plant.