In general, a different pattern of

In general, a different pattern of IQI is used in the USA and these are still called penetrameters. There are several minor variations of the same basic design. The best known is the ASTM design, which consists of a unifonn-thickness plaque containing three drilled holes and identification letters (Fig. 7.2). If the plaque thickness is T, the hole diameters are T, 2T and 4Twith an overriding limit that the minimum hole diameters are 0.01 in, 002 in and 0.04 in, respectively. The plaque must be of the same material as the specimen. Normally, a plaque is used such that Tis 2% of the thickness of the specimen and the sensitivity is expressed in the form '(2-2T) level', which means that T = 2% and the 2T hole is discernible on the image. 'Equivalent penetrameter sensitivities' (EPS) are as shown in Table 7.3. According to ASTM Standard E-746-93, EPS(%) values are based onwhere h is the diameter of the smallest detectable hole in a penetrameter step of thickness T with a specimen thickness x. E-747-80 gives conversion charts from wire IQI sensitivities to ASTM levels for different specimen thicknesses.Compared with the European step /hole type of IQI, if a 2% thickness step with its corresponding IT hole was found to be the limit of detection, the ASTM scheme would call this (I-IT) or 1.4% 'equivalent sensitivity', whereas in Europe it would be 2.0% step/hole IQI sensitivity. With any step/hole IQI it is possible to have confusion between the discernibility of a step and the discernibility of a hole, but the two sensitivity values so obtained would be very different. Some US specifications distinguish between contrast sensitivity (judged on step discernibilty) and detail sensitivity (judged on hole discernibility).