Recent improvements to the ASTM-type ultrasonic reference block system

Abstract

Recent activities aimed toward improving the ASTM-type ultrasonic reference block system are described. On the aluminum block system (ASTM E127 and NBS TN 924), efforts were focused on better definition of the measurement equipment (transducer and instrument) , the implementation of a Measurement Assurance Program and Loaner Block Service, and modeling of the distance-amplitude relationship.It is shown that a large increase in the precision of reference block readings is easily achievable by implementing simple changes and controls in the measurement procedure. On steel and titanium blocks (e.g. ASTM E-428) efforts were directed toward quantifying the extent of reproducibility possible among blocks fabricated by both conventional drilling and by diffusion bonding.Reasonable reproducibility is achievable by both, with the diffusion-bonding process offering both advantages and disadvantages.

Heteroscedastic nonlinear regression models based on scale mixtures of skew-normal distributions

“…These data are generated from a National Institutes of Standards and Technology (NIST) study by Dan Chwirut involving ultrasonic calibration (Chwirut, 1979), where the response variable is ultrasonic response y and the predictor variable is metal distance x (see left panel of Figure 4). The data consist of 214 observations, and is available freely in the R package NISTnls .…”

An assessment of ultrasonic reference block calibration methodology

“…6 is the improvement of the uncorrected ceramic data taken with initial sensitivity determined by the block target (diamonds), over that taken with sensitivity determined by the spherical target (triangles). While the subsequent application of correction factors (stars) enhances the agreement with the quartz data (horizontal line) , a very significant factor for improving the agreement between the two transducers' data appears to be the target used to set system sensitivity [19]. Apparently, the spherical target interrogates features of the ultrasonic beam that are distinctive from those interrogated by a flat-bottom-hole in metal and, therefore, the relative echo difference between the two targets does not transfer proportionately when setting system sensitivity with different transducers.…”

“…Pulse width and shape variations, together with receiver nonlinearity, can substantially affect system performance [19]. Specifically, RF pulse width variations have been observed to cause echo amplitude changes on the order of one dB (refer to Table 1 in Section 4.4).…”

an appraisal of current and future needs in ultrasonic NDE standards

“…Several criticisms have been raised regarding the FBH standard. The most prevalent is of the variability of these blocks; however, recent developments provide a mechanism for solving these problems [11,15].…”

“…A comprehensive effort has been launched to improve the overall standardization of ultrasonic systems, standardization of electronic subcomponents and transducers and improved testing practices. The test block effort is still vigorous and there is an active program within ASTM and elsewhere to reduce variability [11].…”