冷却水系水処理剤の銅管耐食性に及ぼすケイ酸塩およびCa硬度の影響

抄録

We examined the suppression of type I” pitting corrosion in copper tubes used for heat transfer in cooling water systems with absorption chillers. We have developed a new water treatment chemical that could inhibit this pitting corrosion. Previously, we investigated the effects of cooling water quality on the effects of the water treatment chemical, and reported a tendency for corrosion inhibition with increasing calcium hardness. In addition to calcium, silicate has been reported as a corrosion inhibitor in water quality components, but there have been no reports regarding the relationship between silicate and water treatment chemical with regard to effects of silicate on pitting corrosion. In this study, the effects of calcium hardness and silicate concentration on the carbon film–dependent pitting corrosion inhibitory effects of water treatment agents for cooling water systems were investigated. The results showed that the breakdown potential increased with increasing silicate concentration, and silicate was effective in preventing corrosion by the water treatment agent. In addition, when the silicate concentration was high, the potential tended to be low when the calcium hardness was high, and conversely tended to be high when the calcium hardness was low. These observations suggested that film formation differs depending on the ratio of calcium to silicate present. The anticorrosion effect was considered to be due to the synergistic effect of 1–hydroxyethane–1,1–diphosphonic acid (HEDP), benzotriazole (BTA), calcium hardness, and silicate contained in the water treatment chemical.