An apparatus for studying formation of calcium carbonate scale on polymer tubes

An apparatus was designed to study scaling of polypropylene and copper tubes during continuous exposure to mildly supersaturated tap water for six weeks. The mild supersaturation (S∼4) is at the high end of the range of supersaturations found in potable water in the US and is a departure from the common practice of testing under accelerated, high supersaturation conditions. In addition to creating conditions closer to practice, low supersaturation conditions are also expected to make the surface chemistry of the tube a controlling factor in the scaling process, and may possibly reveal differences between polymers and metals. The apparatus employs a continuous flow of tap water with in-line injection of chemicals to adjust and control supersaturation, and an in-line heater to boost the temperature of the water to 40°C. The higher temperature enhances the kinetics of the scaling process without severely affecting the thermodynamic surface parameters that affect scale nucleation. Multiple tubes are exposed simultaneously. Test results show that the apparatus operates with stable flow rates, calcium ion concentration and temperature, indicating that it is ready for long term experiments.