The method of classification given in this part of ISO 4433 serves to determine the chemical resistance of unplasticized poly(vinyl chloride) (PVC-U), high-impact poly(vinyl chloride) (PVC-HI) and chlorinated poly(vinyl chloride) (PVC-C) pipes designed for the conveyance of liquids in the absence of pressure and stress (e.g. due to earth loads or traffic loads, dynamic or internal stresses). To determine the chemical resistance, the method uses the change in mass and the changes in tensile properties which result from the immersion of test pieces, taken from such pipes, in liquid chemicals. The immersion test is carried out in accordance with ISO 4433-1. This part of ISO 4433 is also applicable to PVC-U sheets as appropriate.