Calcium sulfate scale deposition on coated carbon steel and titanium

Scaling/fouling is a thermal barrier in heat transfer equipment which badly impedes heatexchanger efficiency and renders production losses. The application of thermally conductive polymer coatings on low-cost materials is common to cope with the problem of fouling and corrosion, and is also a cost-effective alternative for the replacement of expensive materials in petroleum industry. Calcium sulfate (CaSO₄) is one of the commonly found scales in Arabian Gulf region. An experimental study was undertaken using rotating cylinder electrode equipment to assess the performance of a polymer (SAKAPHEN Si57E) coating applied on carbon steel with regard to CaSO₄ scaling on coated steel and titanium metal. The scale was obtained at 60°C, atmospheric pressure and at various rotational speeds ranging from 100 to 2,000 rpm on both the materials. The results of the study showed that the growth of calcium sulfate scale on bare titanium metal increased significantly while it remained almost invariant on the coated carbon steel surface, with increasing rotational speeds. The anomalous behavior of coated steel samples was attributed to the competing effect between scale deposition and scale removal process due to the fluid flow and to the coating's antifouling characteristics, which resulted in less scale adhesion on coated steel compared to bare titanium metal surface. In addition, the field performance and economic appraisal of the selected coating are presented, as well.