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.Résumé : Cette étude a été entreprise afin d'évaluer, dans l'eau du Greater Vancouver Water District, l'efficacité de l'othophosphate de zinc, du silicate de sodium de type N et d'un mélange commercial des deux produits comme agents anticorrosifs dans les limites qu'un système pilote ayant sept boucles pourra permettre. Dans toutes les boucles, à l'exception de la boucle de contrôle contenant de l'eau brute, le pH et l'alcalinité ont été ajustés, et l'eau a été désinfectée avec 2,5 mg/L de chloramine (NH 2 Cl). Les taux de corrosion du cuivre et du fer fondu ont été mesurés pendant 12 mois sur des pièces de conduites, enlevées à des intervalles de trois mois, et aussi en utilisant un instrument qui mesure la résistance électrique des conduites. Des échantillons d'eau stagnante récoltés des soudures articulées de plomb/étain, de rouleaux de cuivre tendre de plombage, de rouleaux submergés de soudure 50/50 plomb/étain, et des robinets utilisés dans chaque boucle ont été régulièrement analysés pour le niveau de plomb, zinc et cuivre. Les résultats de perte de masse des pièces de conduites indiquent que tous les agents anticorrosifs, en particulier l'orthophosphate de zinc, ont agit favorablement avec le cuivre, mais n'ont fourni aucun effet bénéfique additionnel à celui obtenu uniquement de l'ajustement du pH et de l'alcalinité pour le cas du fer fondu. Cependant, quelques niveaux très élevés de métal ont été mesurés dans des échantillons d'eau stagnante obtenus des boucles contenant des agents anticorrosifs. Généralement, les résultats ont confirmé que l'ajustement du pH et de l...

IRON PIPE corrosion IN DISTRIBUTION SYSTEMS

“…Other studies found lower iron concentrations (Volk et al, 2000) and fewer customer complaints of red distribution systems distribution systems water (Horsley et al, 1998) during the colder winter months. Finally, two pilot-scale studies saw peaks in turbidity (Smith et al, 1998) and metal concentrations (MacQuarrie et al, 1997) that appeared to correlate with temperature changes.…”

Nitrification and potential control mechanisms in simulated premises plumbing

“…Ammonia has a strong complexation constant for cupric ion (Schock et al, 1995). On the other hand, according to MacQuarrie et al (1997) and Rahman et al (2007), application of monochloramine results in a decrease in copper pipe corrosion. Current results found higher total and dissolved copper concentrations in the reactors where the disinfectant was added.…”

Use of polyphosphate in corrosion control

“…This analysis will shed light on what percentage of the phosphorus is contributed by orthophosphates and what percentage by polyphosphates. Flow‐through test and monitoring loops as described in the AWWARF loop model provide a more consistent and accurate picture than that offered by coupon testing. Furthermore, flow‐through loop testing and coupon testing have been found to yield contrary results, as demonstrated by the 1993 Madison utility corrosion control study and other research 21 Tests should run until a steady state of pipe metal concentration in the water is reached.…”