For foam core pipes, particularly those used in drainage, waste, and venting (DWV) or sewer applications, the structure of the foam core is critical for performance. A key requirement is the presence of a closed-cell structure within the foam.
A core with insufficient resistance against shear forces can lead to the skins acting independently, reducing the actual stiffness compared to the calculated stiffness. Crucially, if the cells within the foam core are open rather than closed, axial leakage can occur through the foam material. This means liquids or gases could potentially travel along the length of the pipe within the foam layer.
To prevent this issue, standards for foam core pipes often include specific requirements related to the cell structure. For example, in the ASTM standard (since 2012), there is a requirement for closed cells. This requirement is verified through a test designed to detect axial leakage. The test involves subjecting a pipe sample to water pressure and checking for leaks.