**5. Porosity inspection**

Procedures for porosity inspection in castings are specified under the relevant industry standard, depending on the material, thickness of the casting and the radiographic technique used. These procedures, based on the ASTM standards, are listed in **Table 2** for different part thicknesses.

In this Chapter, reference will be limited to the ASTM E2868 standard (Standard Digital Reference Radiographs for Steel Castings Up to 2 inches (50.8 mm) in Thickness). This is the equivalent of ASTM E446 for film radiography, both of which are similar to their heavy-walled counterparts. The approach developed here can therefore be applied to any of these standards. The ASTM E2868 standard provides a set of five digital reference radiographic images (nominal 250 kV X-rays) for each type of shrinkage porosity (CA - linear, CB – feathery, CC – sponge, CD – combined) from the lowest severity level 1 to the highest severity level 5 (as shown in **Figure 15** for the case of sponge shrinkage porosity), for comparison with production radiographs. The reference radiographs can be generated for a comparable resolution (pixel size) to that of the production radiographs.


Production radiographs are commonly obtained using conventional X-ray techniques. Lately, X-ray Computed Tomography (CT) is gaining popularity for internal defect identification [23]. Reasons include the ability to determine pore morphologies in 3D, and resolutions as low as 1 μm (voxel size) suitable for microporosity detection. For comparison with reference radiographs as per the industry

*Original (left) and contrasted (right) 100 μm resolution ASTM E2868 digital reference radiographs for*

*Shrinkage Porosity in Steel Sand Castings: Formation, Classification and Inspection*

*DOI: http://dx.doi.org/10.5772/intechopen.94392*

*shrinkage porosity Category CC (sponge), severity levels 1–5.*

**Figure 15.**

**149**

**Table 2.**

*ASTM standards for film and digital radiography of steel castings.*

*Shrinkage Porosity in Steel Sand Castings: Formation, Classification and Inspection DOI: http://dx.doi.org/10.5772/intechopen.94392*

**Figure 15.**

permeability of the interdendritic region, in terms of SDAS, solid fraction

interdendritic regions (as a result of pressure drops in the high-solid fraction region of the mushy zone), the resulting effect is that of a partially drained sponge, and hence the term "sponge porosity" for this defect (see **Figure 8**).

• In short freezing range alloys, the smoother solidification fronts lead to linear shrinkage defects, often of a feathery morphology. With low solidification rates, due to larger dendrite sizes and ensuing coarsening/remelting of neighbouring dendrite arms. A linear morphology prevails – **Figure 14**.

Procedures for porosity inspection in castings are specified under the relevant industry standard, depending on the material, thickness of the casting and the radiographic technique used. These procedures, based on the ASTM standards, are

In this Chapter, reference will be limited to the ASTM E2868 standard (Standard

**Thin-walled Heavy-walled Heavy-walled**

Digital Reference Radiographs for Steel Castings Up to 2 inches (50.8 mm) in Thickness). This is the equivalent of ASTM E446 for film radiography, both of which are similar to their heavy-walled counterparts. The approach developed here can therefore be applied to any of these standards. The ASTM E2868 standard provides a set of five digital reference radiographic images (nominal 250 kV X-rays) for each type of shrinkage porosity (CA - linear, CB – feathery, CC – sponge, CD – combined) from the lowest severity level 1 to the highest severity level 5 (as shown in **Figure 15** for the case of sponge shrinkage porosity), for comparison with production radiographs. The reference radiographs can be generated for a comparable

Standard (film) reference radiographs ASTM E446 ASTM E186 ASTM E280

ASTM E2868 ASTM E3030

• In long-freezing-range alloys, due to inefficient liquid feeding of the

distribution and point of coherency.

*Casting Processes and Modelling of Metallic Materials*

*Morphologies of linear (left) and feathery (right) shrinkage porosity.*

listed in **Table 2** for different part thicknesses.

resolution (pixel size) to that of the production radiographs.

*ASTM standards for film and digital radiography of steel castings.*

**5. Porosity inspection**

Standard digital reference

radiographs

**Table 2.**

**148**

**Figure 14.**

*Original (left) and contrasted (right) 100 μm resolution ASTM E2868 digital reference radiographs for shrinkage porosity Category CC (sponge), severity levels 1–5.*

Production radiographs are commonly obtained using conventional X-ray techniques. Lately, X-ray Computed Tomography (CT) is gaining popularity for internal defect identification [23]. Reasons include the ability to determine pore morphologies in 3D, and resolutions as low as 1 μm (voxel size) suitable for microporosity detection. For comparison with reference radiographs as per the industry
