Basically porosity, regardless of cause, can be classified as:
1.
Enclosed Porosity
This type would not cause a problem in a casting unless it is exposed in a subsequent machining operation.
2.
Blind Porosity
Blind porosity can lead to internal corrosion, spotting or blow-out of any finishing coating.
3.
Through Porosity
This sometimes occurs in as-cast areas of castings, but usually appears in machined areas. This type of porosity will obviously cause leakage through a wall section of an otherwise sound casting, which must be scrapped or reclaimed by impregnation.
