Effect of Elevated Temperature on Stress-Rupture Testing of Low Inherent Viscosity PVC Resins

Stress-rupture testing is generally performed on pipe and fitting compounds designed for pressure applications. Per PPI TR-2, the PVC resin in the compound formulation is required to have an inherent viscosity (IV) of 0.88 or greater and is sometimes referred to as ‘pipe grade’ resin. These compounds obtain a hydrostatic design basis (HDB) rating at 73oF (23oC) per ASTM D2837 and have a maximum recommended service temperature of 140oF (60oC). PVC compound made from lower inherent viscosity resin (IV generally between 0.65 and 0.88 also called ‘fitting grade’ resin) are used primarily in the manufacture of fittings and are not required to undergo stress-rupture testing. The primary objective of this study is to verify that stress-rupture testing can be performed on a fitting grade resin at the maximum recommended service temperature (60oC) without the development of a knee. The secondary objective is to compare the effect of the outside testing environment (air bath versus water bath) when testing at elevated temperature. Testing is therefore performed per ASTM D2837 on pipe specimen molded from a fitting grade resin at four different conditions : two different temperatures (23oC and 60oC) in two different outside environments (air bath and water bath).