Apparent porosityis a measure of the volume of open pores (voids that can absorb water) within a refractory sample, relative to the total volume. It is always expressed as apercentage. Testing is done using standards such as ASTM C20, which API 936 references. This metric is crucial for understanding a material's permeability, thermal shock resistance, and mechanical integrity.
Reference:
API Std 936 - Testing Procedures section referencing ASTM C20: "Porosity shall be reported as percent volume open porosity." API TR 978 - Section on Physical Properties of Monolithic Refractories