Assessment of the state of surface roughness for ultrasonic testing

Application of surface roughness samples (comparison).

By comparing with them, you can approximately estimate the state of surface roughness. Finding by comparison the closest suitable sample by sight or by touch, as they say in such cases – organoleptically – they evaluate the roughness of the desired surface, if the roughness samples are made at a specialized enterprise, have been verified by standards and have a valid metrological certificate.

Many, even experienced, flaw detectorists consider the use of roughness samples to be quite sufficient, but, as a special study shows, this is not the case, and the error from underestimating the difference arising from the difference in roughness and waviness of the surface of the HO and the input surface of the y-sound of the OK can be significant. For under-rejection and skipping a dangerous defect, discrediting the ultrasonic testing method as a whole.

The normative documentation establishes only the maximum permissible level, which the norm for roughness and waviness must comply with. And, if with the help of subjective organoleptics we estimated the surfaces of HO and OC, then how to take into account the contribution to the measured amplitude when these parameters of HO and OC differ?

As a rule, the OC surface is worse than the HO surface, so the actual detectability of defects is much lower than prescribed by the RD. The difference can be so significant that its underestimation is fraught with an obvious error in measuring the amplitudes of echo signals. Therefore, the use of roughness samples does not completely solve the problem of the difference between the roughness and waviness of HO and OC.