**6. Summary**

standards, 3D CT scans can be collapsed into equivalent 2D images, using a "thick

(pixel or voxel size) – however, it may not be possible to generate such high resolution production radiographs in practice due to equipment limitations, especially in the case of high density materials such as steels. Hence, a 100 μm resolution is seen as adequate for detection within the typical SDAS length scale (for ferrous

The standard digital reference radiographs provide resolutions as low as 20 μm

Allowable porosity levels are often based on client specifications, but may also be part of quality standards associated with particular components. Such acceptance criteria, as in the case of high-performance valves for example, are shown in

The inspection process requires the area of the production radiograph to be

*Acceptance criteria for shrinkage porosity in steel valve castings of wall thickness* ≤ *50.8 mm (ASME B16.34),*

*Evaluating the porosity severity level by comparing the production radiograph with the reference radiographs of comparable resolution (e.g. 100 μm = 10 pixels/mm) from ASTM E2868, for a particular category of*

prorated to an area of interest of the reference radiograph, as illustrated in **Figure 17**, and visually compared to establish the matching severity level.

slab" feature of CT scanning image analysis software [24].

*Casting Processes and Modelling of Metallic Materials*

metals).

**Figure 16**.

**Figure 16.**

**Figure 17.**

**150**

*shrinkage porosity (e.g. CD - combined shrinkage porosity).*

*showing the critical regions on the right.*

An overview of shrinkage porosity is given, with reference to steel sand castings, from investigating the causes of shrinkage porosity to possible mitigation approaches, and finally the importance of understanding the technologies associated with the inspection and evaluation of shrinkage porosity severity levels. Further analysis of certain aspects of shrinkage porosity may be undertaken where an in-depth understanding is required. In summary, the following points are noted:

