Page 90 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Non-destructive and Destructive Testing

1. Density is a measure of how much light passes through
the film. The higher the density number, the darker the
film. Normal acceptance levels are densities of between
1.8 minimum to 4.0 maximum for X-ray and 2.0 to 4.0
for gamma, but it varies between standards. The density
measurement is normally taken along the area of interest
(i.e. the weld length) using a piece of equipment called a
densitometer.
2. Sensitivity is an indication of the smallest defect that can
be seen on the image. A wire type or hole type image
quality indicator (IQI) is used to determine the smallest
defect visible on the image. The wire type IQI is the more
common type used and consists of either six or seven
wires depending on the standard used (see Fig. 6.5). The
American ASTM standard specifies six wires but the
European standard specifies seven. Sensitivity is
expressed as a percentage derived from the thinnest
wire visible divided by the material thickness. The
acceptable percentage will vary depending on material
thickness. To save calculations ASME V and EN
standards give tables specifying the smallest wire that

Figure 6.5 Image quality indicator (IQI)

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200906QG Welding chap6.3d Page 75 of 87