F-EX-1-9 Seawater Studies of Fouling on Copper and Its Alloys
An HTRI Portable Fouling Unit was operated on untreated seawater at the Haynes Steam Plant, a power plant of the Los Angeles Department of Water and Power at Long Beach, California. Seven tests were conducted to study crystalline fouling comparing Alloy 796 and 443. Four tests studied the effects of velocity comparing Alloy 706 and titanium. Surface temperature effects were studied in five tests comparing Allow 706 and titanium. The crystalline fouling tests and three of the velocity effect tests were reported in HTRI Report F-EX-1-5. The final velocity test and the surface temperature tests comparing Alloy 706 and titanium are described in this report.
At the Haynes Steam Plant the surface condenser operates with a velocity of 6 ft/sec (1.8 m/s) and an average surface temperature of 80 °F (27 °C). PFRU operating conditions for the velocity and surface temperature tests bracketed the plant conditions. Velocities of 2, 4, 6, and 8 ft/sec (0.6, 1.2,1.8, and 2.4 m/s) were tested at surface temperatures of 80 °F (27 °C). And surface temperatures of 80, 100, 130, and 150 °F (27, 38, 54, and 66 °C) were tested at a velocity of 6 ft/sec (1.8 m/s). Biological deposit analyses were made at the end of several tests.
Fouling rates for Allow 706 and titanium decreased with increasing velocity. At a given velocity, titanium fouled at a steady rate. Below 6 ft/sec (1.8 m/s), Allow 706 fouled at approximately the same rate as titanium but only for short Periods of time. Periodically the fouling deposit on Alloy 706 suddenly decreased. Above 6 ft/sec (1.8 m/s), Alloy 706 also fouled at a steady rate without periodic falloff. The periodic loss of deposity was caused by the binding organisms failing to survive the toxic surface of Alloy 706.
At a surface temperature of 80 °F (27 °C) and a velocity of 6 ft/sec (1.8 m/s), alloy 706 fouled at about half the rate of titanium. At 100 °F (38 °C) Alloy 706 and titanium fouled at the same rates. The decrease in biological fouling was offset by increased corrosion of Alloy 706 at 100 °F (38 °C). At 150 °F (66 °C) Alloy 706 had only corrosion fouling. Deposit analyses showed mostly corrosion products on Alloy 706. The deposits on titanium were silt particles bound together by fibrous marine growths.