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In Algeria, high-density polyethylene (HDPE) is widely used in drinking water pipes. This study is focused on the precipitation of calcium carbonate, a major constituent of scale, from calcocarbonically pure (CCP) water in HDPE pipe. Studying scaling in natural conditions is very difficult because it occurs over many years. For this, accelerated scaling is caused by the degassing CO2 dissolved in water. The kinetic study has shown that the germination time and the critical pH decrease with the hardness (30, 40 and 50 °f) and temperature (30, 40 and 50 °C) of water. On the other hand, scaling process efficiency (η) and the supersaturation coefficient (Ωcal) of CaCO3 increase with these parameters. The CaCO3 precipitation occurs both in solution and on walls of HDPE. By the weighing method, it is shown that the deposit mass increases with hardness and temperature. Calcium carbonate precipitates much more in homogeneous phase than in heterogeneous one. The study also showed that heterogeneous nucleation on HDPE is much less important than on PA, PVC, chrome and Inox. These measurements are supported by the characterization of X-ray diffraction deposits and by scanning electron microscopy, which recognizes that the precipitate obtained consists mainly of calcite.

Scale precipitation on HDPE pipe by degassing of CO2 dissolved in water