As HOBAS pipe systems are used for the transport of different liquids including acidic or alkaline sewer aggressive chemical solutions as acids and bases it is necessary to know about the chemical resistance of the used composites. Therefore HOBAS Engineering GmbH ordered an investigation of the chemical resistance from different materials according to EN 13121-2 (GRP tanks and vessels for use above ground Part 2: Composite materials Chemical resistance). The used standard allows a valuation of materials by appraisal of optical and mechanical attributes. The optical evaluation of the specimens was made according to the standard EN 13121-2. As this is a quiet subjective test method, a picture was made of all specimens. Also a picture was made of all pipe segments used for the internal pressure test after they failed. The aim of the investigations is to calculate a factor of deterioration (A2) for chemical solutions. As the tests were made for two different resin types, three different fibre types, fife chemical solutions and three temperatures it was useful to measure only combinations of these parameters which are expedient. The investigations show that the mechanical parameters crucial for the factor A2 than the optical parameters.. Especial the bending strength shows a significant time dependent decrease. Also the bending E-Modulus shows a significant time dependent decrease but a lower decrease as the bending strength.