Corrosion Control in Water Pipes by Adjusting the Corrosivity of Drinking Water : Effect and impact of the Corrosion Inhibitor

The tap water used in Seoul was found to be corrosive. Its corrosivity was effectively reduced by that the additions of alkali agent such as NaOH, Ca(OH)2 and corrosion inhibitor such as H3PO4. For the corrosion test, carbon steel pipe 50 m long was exposed to the drinking water produced by a pilot plant at 36.5 ℃, similar to the existing process where it takes about 20 minutes to reduce the initial chlorine content of 0.5 ㎎/L to 0.05 ㎎/L. CO2 and Ca(OH)2 was added not only to control the Langelier index (LI) above -1.0 and but also, to increase the duration time of residual chlorine by about 6 times. The persistence effect of residual chlorine was in the order of H3PO4 > Ca(OH)2 > NaOH. Measurements of weight loss showed that corrosion inhibition was effective in order of Ca (OH)2 > H3PO4 > NaOH > no addition, where the concentrations of Ca(OH)2 and phosphate were 5 ~ 10 ㎎/L (as Ca2+) and 1 ㎎/L (as PO43-), respectively.