In all relevant standards for the requirements of PVC-U pipes homogeneity of plastification is required examined by Dichlormethane test (DCMT). Because of low reliability in Round Robin Tests other methods to assess homogeneity like DSC method acc. ISO 18373-1, ISO/DIS 18373-2 were introduced. Aim of this work is to study the influence of OBS and lead stabilizers on the degree of gelation. Both DCMT and DSC analysis were applied and the results compared. At locations of break in internal pressure tests the gelation, creep-behaviour by use of fracture toughness, viscosity measurement, light microscopy and tensile test were applied.