F-EX-1-5 Fouling Research on Copper and Its Alloys - Seawater Studies

R. B. Ritter and J. W. Suitor

INCRA is sponsoring a study by HTRI to investigate seawater fouling of copper-bearing and competitive heat exchanger tube materials using an HTRI-designed Portable Fouling Research Unit (PFRU). The unit has been operating at the Haynes Steam Plant, a Los Angeles Department of Water and Power (LADWP) poser plant in Long Beach, California. This report covers all activities and findings from the start of the study in January 1974 through February 1976.

Fouling results show that crystalline fouling is not a problem at surface temperatures below 225 °F (107 °C). Analyses of deposits showed mostly corrosion products and silt with no calcium sulfate crystals. The major fouling problem was found to be silt particles bound together by organic growths. Many marine organisms secrete material that cement them to extraneous objects. This bioadhesion, combined with small bits of debris, accounts for the persistent fouling at water velocities that would normally sweep away such silt deposits. Bioadhesion occurred on both Copper Alloy 706 (90-10 Cu-Ni) and titanium test rods, but Copper alloy 706, because of its copper content, did not harbor the organisms for extensive periods of time. Each increase of 2 ft/sec (0.6 m/s) in velocity resulted in a 50 percent reduction of the fouling rate at the lower velocity. The overall fouling rates for titanium were about 2.4 times those for Copper Alloy 706 at 2, 4, and 6 ft/sec (0.6, 1.2, and 1.8 m/s). In non-heat transfer tests of tube materials suspended in the channel, a titanium tube collected a biomass some ten times the diameter of the tube, while the copper alloy tubes had only slight films of corrosion products.