Scale Formation and Mitigation of Mixed Salts in Horizontal Tube Falling Film Evaporators for Seawater Desalination
This paper describes an investigation into the interrelationships between the performance of an impressed current cathodic protection (CP) system and the deposition of scale compounds in a seawater pipe system. Some experiments were conducted on a laboratory set-up but the emphasis was on tests on a 0.25 m diameter steel pipe fed by seawater flowing to a thermal desalination plant. The experimental approach involved monitoring the CP current as a function of time at various set potentials and correlating this data with evidence from visual inspection of the pipe-wall surfaces and small probe specimens. The influences of control potential and seawater flow rate at temperatures of 25-35 degrees C were studied. Selected scale samples were subjected to examination by scanning electron microscopy and X-ray diffraction. The overall findings are discussed in terms of fundamental scale/CP-operation interactions and aspects relevant to practical operation of CP systems on seawater pipe installations.