E746 is a practice with uses the concept of relative image quality response (RIQR). The results of the evaluation can be transfered to the equivalent penetrameter sensitivity (EPS) described within Practice E1025.
The basic idea of this test is to get a statistic within one IQI evaluation. Therefore a set of multi hole plates are used where the inspector has to count in a row of holes with same diameter the amount of holes which he could clearly identify. The 50% level of the plate type and row number leads to the EPS value.
Within E746 there are two versions of sets of the plates, one made of stainless steel and one made of plastic.
In E1735, which is intended for energies above 4 MeV, is a very similar set of stainless steel with other thicknesses of the plate.
Here is a photo of the four E746 plaques from stainless steel on a 19mm steel plate and an X-Ray image taken with a DDA in positiv display with a small highpass filter to emphasize the visibility of the small holes:
The four plates come in a wooden box.
The thickness of the plates decrase (yellow: E1735)
.................................. and same for the hole sizes in the rows (yellow: E1735)
As it is easy to see all holes when you radiograph them directly, E746 requires that you put the stainless steel plaques on an absorber steel plate with 19mm thickness or the plastic plaques on a 35mm plastik plate made of polymethylmethacrylate (PMMA). In your own interest the absorber plates should cover the complete detector and the two surfaces of the absorber plates shall be smooth - ground finish Ra 6.35µm is required. If it would be larger it may be visible in the image as grain structure or simply noise. For E746 the acceleration voltage is set to 200kV for the steel plaques and to 30kV for the plastic version. Place the plaques on the source side of the absorber plates.
The absorber base plate for the E1735 version shall have a thickness of 15cm (6 inch) and shall be made of stainless steel. The requirements for size and ground finish are similar to E746.
The contrast in [%] for the different plaques is shown in the table above. It starts at 2% and goes down to 0.68% which is really challenging for all X-Ray techniques without DDAs. In the MeV range the requirements are even tougher ... .
In the
it is shown that the visibility depends on contrast to noise and spatial resolution. To avoid that the limited spatial resolution dominates the visibility, you should have enough pixel insides the holes. The right table shows the amount of pixels which cover the same geometrical area as the hole - depended on the pixel size of the used digital system in µm. E.g. if you want to see the smallest holes with a diameter of 0.5mm you will have with a 100µm pixelsize detector 20 pixels covering the hole - and the edge pixels are inside this number.
The energy level for E746 is very restrict - chapter 6 describes a method for calibration of the X-Ray source with half value layers of copper for the 200kV and with an Aluminum plate for the 30kV version. Due to my experience the X-ray generators are quite good in providing the correct kVs - if you could prove the energy level in a different way, it is okay (see 6.5). For the MeV Sources there is no requirement to validate the energy level.
Last edited by admi on 17.03.2020, 21:20, edited 5 times in total.
Reason: added contrast in table 1 and #pixels in table 2