Greater Vancouver Water District drinking water corrosion inhibitor testing

Abstract

This study was initiated to evaluate, in Greater Vancouver Water District water, the effectiveness of zinc orthophosphate, type N sodium silicate, and a commercial blend of the two as corrosion inhibitors within the limitations that a seven-loop pilot plant would allow. In all but the raw water control loop, pH and alkalinity were adjusted, and the water was disinfected with 2.5 mg/L of chloramine (NH 2 Cl). Copper and cast iron corrosion rates were measured over the course of 12 months on pipe inserts removed at 3-month intervals and via weekly monitoring using an electrical resistance measuring device. Standing water samples taken regularly from lead/tin solder jointed, soft copper plumbing coils, from submerged free standing coils of 50/50 lead/tin solder, and from faucets on each loop were measured for lead, zinc, and copper levels. The results of the weight loss determinations from the pipe inserts indicated that all of the inhibitors, particularly the zinc orthophosphate, worked very favorably with copper, but they offered no additional benefit over that obtained from the pH and alkalinity adjustments alone, in the case of the cast iron coupons. However, some very high metal levels were measured in the standing water samples from some of the inhibitor loops. Generally, both the coupon and leaching results confirmed that pH and alkalinity adjustment and disinfection with chloramine, instead of chlorine, will reduce pipe metal corrosion.