Figure 6-30. Effect of Development Time upon Film Speed, Contrast and Fogging.
Use the IQI specified in the technique. Consult with the appropriate ALC NDT
Level III for instructions if the IQI identified in the technique is not available. IQIs
are not generally required for inspection for the presence of debris, for proper
assembly of components, for dissimilar material inspection, for honeycomb
structures, or for the presence or absence of material.
There is a need to be able to qualitatively define how sensitive a radiographic image is. The devices that achieve this
aim are known as penetrameters. Another description is image quality indicators (IQI). By whatever name, they
provide an indication of what the film reader can be expected to see in the actual part being inspected. A wide range of
penetrameters is specified for use by various industries. ASTM plaque-like type penetrameters (or as now more
commonly called image quality indicators) are described in Ref. 13. Wire penetrameters, particularly useful for weld
inspection, are described in Ref. 14. In their current form, penetrameters are a small plaque, fabricated of the same
material as that being radiographed. The thickness of the penetrameter is a known percent of the test object thickness.
Holes in the penetrameter are of diameters 1T, 2T, and 4T when T equals penetrameter thickness. Thickness
visualization of these holes can be related to the sensitivity of the radiographic image. A typical penetrameter is shown
in Figure 6-31.