Surface preparation under ultrasonic control
According to almost all industry normative documents, surface preparation for ultrasonic testing is the responsibility of the organization that installed the equipment.
The responsibility of the flaw detectorist includes, as an indispensable condition for the successful implementation of ultrasonic testing, quality control of surface preparation.
The quality of surface preparation for introducing ultrasound into the test object – OK – pipe, weld, forging, sheet – directly depends on the success of its ultrasonic testing.
In addition, when performing ultrasonic testing, industry standards establish requirements for the waviness of the ultrasound input surface. Most industry standards use a waviness standard of 0.015.
So, the standards for roughness Rz = 40 μm and waviness 0.015 are set, but how can they be ensured in order to correctly measure the value of the equivalent area of the defect in the continuity of the OC material – is it acceptable according to ND or, if it is incorrectly assessed by measurement, there will be a danger of destruction of the responsible OC?
In the case of increased values of roughness and waviness of the ultrasound input surface, the amplitude of the echo signal from the found and fixed defect can be measured and estimated incorrectly – with all the consequences.
The degree of acoustic transparency of the contact layers of surfaces during adjustment and control of the sample and OC may differ from each other, and the ultrasonic testing data may not be reliable.