Corrosion Results & Ryznar Stability Index
The test conducted by using corrosion coupons indicated that corrosion rate was less than 1MPY most times. The highest corrosion rate, 3MPY , belonged to just one plant . Apart from coupon test , Ryznar Stability Index ,RSI, Which determines corrosive or scaling tendency of water was calculated in 13 months. Using the available sources and the conducted studies, the optimal range of RSI was found to be between 5.5 to 6.5, in that case water has neither corrosive nor scaling tendency. Results show that seven out of the eleven plants, the RSI monthly mean index had constantly remained at the optimal level of 5.5-6.5 during the control period. It is important to note that no month's average was within the corrosive or scaling limit. In one plant 92 percent (12 months) of monthly mean indices were inside the appropriate limit.LD plant with a monthly average RSI of 70 percent within the optimal range, had the lowest standing among plants. PP and HD plants, 77 percent of the time were in that range. Generally , considering that every plant achieved more than 70 percent of the suitable level on Ryznar Stability index , also, with a view of coupon test results , it seems that the results of corrosion and scaling control in water cooling towers had been successful, with changing the method of microorganisms control.