Corrosion indices as a method of corrosion measurement and a systems operating tool

Abstract

Under grants from the USEPA and South Carolina Department of Health and Environmental Control (DHEC) a corrosion control study was conducted in two community water distribution systems, Montmorenci‐Couchton (MC), a medium‐size system; and Midland Valley (MV), a small‐size system. The source waters of both systems are low in pH, low in alkalinity and low in dissolved solids. The treatment schemes consisted of pH adjustment with lime, and chlorination with HTH at MC, and pH adjustment with soda ash, chlorination with HTH, and polyphosphate addition at MV.

Using the data obtained over a period of 5 months, various corrosion indices were calculated and results were compared with coupon test assemblies. Corrosion indices indicated that the finished waters of both systems were aggressive, whereas corrosion control films were observed in coupon inserts. Statistically significant relationships between various indices were obtained for both systems. Analysis of lead and copper levels in tap waters of both systems, revealed that both systems meet the 1991 lead and copper action levels.

Key words:

• corrosion
• corrosion measurement
• corrosion indices
• saturation index
• coupon
• lead and copper rule
• water treatment
• inhibitor