Abstract
Titanium metal has been used extensively for heat exchanger tubes in MSF-type desalination plants in Middle East countries. This is mainly due to its excellent erosion-corrosion resistance and good heat transfer properties. In an MSF plant, during desalination processes progressive build-up of scale occurs inside the tubes, and the cleaning of tubes by descaling is an essential maintenance operation. The scales mainly consist of CaCO 3 and Mg(OH) 2. The descaling is usually carried out by using an inhibited acid. This paper presents the results of a study aimed to determine the feasibility of using inhibited H 2SO 4 as an effective and trouble-free descalant. An investigation was undertaken to study the corrosion behavior of titanium metal in H 2SO 4 solution inhibited with CP-20, a β-ethyl phenyl ketocyclohexyl amino hydrochloride based commercial inhibitor. The studies were carried out at 50°C under deaerated and atmospheric exposure conditions applying immersion and potentiodynamic polarization and Tafel plot techniques. The possibility of hydrogen absorption or hydride formation in titanium metal was also considered under test conditions. For comparison, the corrosion behavior of carbon steel (flash chamber material) and aluminum bronze (tube sheet and water box material) were also studied under identical conditions. The results of immersion tests show a zero corrosion rate for titanium under normal or deaeration conditions since no perceptible weight change was observed. The electrochemical tests show corrosion rates below 0.1 mpy (0.0025 mm/y), which indicates outstanding resistance of the metal. Extremely low corrosion rates of titanium in inhibited H 2SO 4 under testing conditions (50°C, normal/deaerated, 0.5% H 2SO 4, dynamic) indicate virtually no hydrogen absorption in the metal. Also, the analytical determination of hydrogen absorption in acid-treated titanium under the aforementioned conditions shows no hydrogen pick-up.
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