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A common way to express the durability of a plastic material is to present a long-term strength diagram for different temperatures for well made straight pipes. In the case of materials for hot-water pipes, the testing time must be longer, and the tests must also be completed with bent and notched pipes, and tests in water completed with additives reducing the surface tension. Examples and test methods are given in the paper. Comparisons between testing with water or air outside the pipes at high temperatures are also made.
A way to measure the thermostability and lifetime of a material or product is to use induction time in differential thermal analysis (DTA) or differential scanning calorimetry (DSC). This method must be used with greatest care and only together with other long-term tests. The use of Arrhenius plots at high temperatures to predict lifetimes of pipes is not helpful. Examples are given in the paper.
DTA or DSC induction tests are however very useful in production control and in, for example, testing of antioxidants resistance to extraction into water. When the type tests mentioned above have secured the possibility of a long service life of the material, the quality control methods (short-term production control tests) shall ensure that production quality is the same as the type tested quality. The correspondence between long- and short-term tests must then be proven. The paper will also deal with these questions.
quality assurance, plastic pipes, hydrostatic pressure test, plastic tubes, hot-water pipe, flexible pipe
Masters of Science, Chemical Engineering, Materials and Process Development of Plastic Materials, Wirsbo Bruks AB, Virsbo,