EFFECTIVE METHOD OF CORRECTION OF ACOUSTIC LOSSES IN A CONTACT LAYER AT ULTRASONIC FLAW DETECTION
Journal: NDT WORLD
Volume 18 № 3
, 2015
Rubrics: ULTRASONIC INSPECTION
Authors:
Type:
Article
Pages:
from 45
to 46
Status:
Published
Received:
09.08.2015
Accepted:
09.08.2015
Published:
09.08.2015
Language:
Russian
Keywords:
ultrasonic flaw detection, acoustic loss correction, contact layer
Abstract (English):
At ultrasonic flaw detection it is necessary to take into account an acoustic loss in a contact layer, especially for products with a statistically rough surface (roughness, waviness). Using samples with the surface identical to the product’s one is the most desirable variant, it is regulated in many techniques, but in practice in vast majority of cases this is not so. Measurements with profilographs or profilometers are taken on a very small area (less than the piezoelectric transducer size) and cannot give an estimation of a real contact layer condition under the whole transducer area. For integral roughness estimation in “CNIITMASH” the capacitance-type sensor DShV has been developed. The sensor is compatible with flaw detectors of any type; it forms a service signal with amplitude that is inversely proportional to a roughness height. Within a frequency rate of 1.8–5 MHz and an incident angle rate of 35–70° the correlation between sensor readings and acoustic losses in a contact layer has been ascertained; a general dependence for them has been obtained, a heuristic equation has been derived and nomograms for piezoelectric transducers of different manufacturers on the sample basis of 123 measurements have been plotted. As a result the new technique of ultrasonic flaw detection has been developed that includes: estimation of tested object real surface roughness with the DShV sensor, flaw detector sensitivity adjustment using a sample with a smooth surface, a gain factor correction by the value taken from a nomogram or calculated on the formula basis. Equivalent defect area should also be measured according to the algorithm described. This technique on principle increases repeatability and reliability of flaw detection results.
At ultrasonic flaw detection it is necessary to take into account an acoustic loss in a contact layer, especially for products with a statistically rough surface (roughness, waviness). Using samples with the surface identical to the product’s one is the most desirable variant, it is regulated in many techniques, but in practice in vast majority of cases this is not so. Measurements with profilographs or profilometers are taken on a very small area (less than the piezoelectric transducer size) and cannot give an estimation of a real contact layer condition under the whole transducer area. For integral roughness estimation in “CNIITMASH” the capacitance-type sensor DShV has been developed. The sensor is compatible with flaw detectors of any type; it forms a service signal with amplitude that is inversely proportional to a roughness height. Within a frequency rate of 1.8–5 MHz and an incident angle rate of 35–70° the correlation between sensor readings and acoustic losses in a contact layer has been ascertained; a general dependence for them has been obtained, a heuristic equation has been derived and nomograms for piezoelectric transducers of different manufacturers on the sample basis of 123 measurements have been plotted. As a result the new technique of ultrasonic flaw detection has been developed that includes: estimation of tested object real surface roughness with the DShV sensor, flaw detector sensitivity adjustment using a sample with a smooth surface, a gain factor correction by the value taken from a nomogram or calculated on the formula basis. Equivalent defect area should also be measured according to the algorithm described. This technique on principle increases repeatability and reliability of flaw detection results.
Keywords:
ultrasonic flaw detection, acoustic loss correction, contact layer
ultrasonic flaw detection, acoustic loss correction, contact layer
1. Shcherbinskii V. G. Influence of acoustic transparency of surface contact layer on flaw detectability in ultrasonic testing. Insight. 1998. V. 40. No. 6. P. 411-417.
2. Shcherbinskii V. G. Ustroystvo dlya ul´trazvukovogo kontrolya sherokhovatosti poverkhnosti izdeliya [Appliance for ultrasonic roughness measurement]. Patent RF, no. 94693. Bull. Izobreteniy [Bulletin of Inventions], 2010, no. 15 (in Russ.).
