RT versus UT – Conversion of acceptance standards from standard reference radiographs (ASTM E446 & E186) into ultrasonic


ASTM E446/186/280 are the most common radiographic specifications for assessment of internal discontinuities in castings. Each of them illustrates various types and degrees of discontinuities occurring in steel castings that have section thickness up to 12 inches (300mm).

This document cover conversion of “reference discontinuities” illustrated in ASTM E446 & ASTM E186 and Severity levels 1, 2, 3 & 4. The worst Severity level 5 is very rarely used and therefore is more less irrelevant nowadays.

The major difference between RT & UT is that Radiographic method is better for detection of discontinuities having major dimension perpendicular to the surface (parallel to the direction of radiation) and Ultrasonic method is better for detection of discontinuities orientated parallel to the surface. However, UT gives more flexibility of inspection by allowing inspection in more direction by using angle probes if necessary. There is undoubtably huge advantage of using UT in comparison to RT, which is much more sensitive and capable of detection planar type discontinuities.

It isn’t possible to convert acceptance standards from reference radiographs exactly into ultrasonic acceptance standards. Different categories of discontinuities (A – Gas, B – Sand and Inclusions, C – Shrinkages with subcategories CA, CB, CC & CD) have different acoustic / reflection characteristics. However, all relevant physical laws have been considered very carefully in this document. Secondly, many years of practical experience from ultrasonic inspection were implemented into this document as well to make it as precise as possible and at the same time practical for ultrasonic inspector.
In many cases two radiographers will sentence the same radiograph differently. Very common is difference of one level in assessment or different characterization of identical discontinuity.

Conversion of Categories A & B is based on acoustic formulas stated in BS EN 583-2 in Table B.1.

Conversion of Category C is based on actual size of discontinuities on reference radiographs.

UT sensitivities are based on experience and specifications BS EN 583-2, ASTM A609 & BS EN 12680-1,2.

This presentation shows that volumetric discontinuities can be successfully assess using ultrasonic inspection. Using UT can make production process more efficient and economical.