Pitting corrosion of copper coiled tubes has been experienced in the air conditioning system having the open heat storage water tank. Although the morphology of the pitting was similar to type 1 pitting corrosion in plumbing copper tubes, the quality of circulating water in the system was different from those in plumbing system and the inner surface of corroded tubes was fully covered with corrosion product occurred for galvanized steel tubes using main plumbing in the air conditioning system.
The factor of the pitting corrosion has been investigated by field test in above actual air conditioning system. The circulating water was more corrosive and contained the fine corrosion-product particles of galvanized steel. The presence of both carbon film and corrosion product of galvanized steel on the copper tubes caused the pitting corrosion. As the pitting corrosion was much influenced by fine corrosion-product particles of galvanized steel rather than carbon film on inner surface of copper tube, pitting corrosion was reduced by entrapping the fine corrosion-product particles of galvanized steel in the circulating water with fine mesh filter.
