Effect of Corrosion Inhibitors on In Situ Leak Repair by Precipitation of Calcium Carbonate in Potable Water Pipelines

Abstract

Corrosion inhibitors can affect calcium carbonate precipitation and associated in situ and in-service water distribution pipeline leak repair via clogging. Clogging of 150 μm diameter leak holes represented by glass capillary tubes, in recirculating solutions that are supersaturated with calcite (Ω = 13), demonstrated that Zn, orthophosphate, tripolyphosphate, and hexametaphosphate corrosion/scaling inhibitors hinder clogging but natural organic matter (NOM) has relatively little impact. Critical concentrations of phosphates that could inhibit leak repair over the short-term in one water tested were: tripolyphophate (0.05 mg/L as P) < hexametaphosphate (0.1 mg/L) < orthophosphate (0.3 mg/L). Inhibitor blends (Zn+orthophosphate and Zn+NOM+orthophosphate) had stronger inhibitory effects compared to each inhibitor (Zn, orthophosphate or NOM) alone, whereas Zn+NOM showed a lesser inhibitory effect than its individual component (NOM) alone due to formation of smaller CaCO particles with a much more negative zeta-potential. Overall, increased dosing of corrosion inhibitors is probably reducing the likelihood of scaling and in-service leak repair via clogging with calcium carbonate solids in potable water systems.

CuO Promotes the Formation of Halogenated Disinfection Byproducts during Chlorination via an Enhanced Oxidation Pathway

“…Anions (i.e., 1 mM, sodium salts of bicarbonate, silicate, phosphate, and chloride) which are prevalent in natural waters (except phosphate) were introduced into the reaction system if required. The presence of silicate can reduce the oxidant decay in copper pipes and phosphate can serve as a corrosion inhibitor in distribution pipes. − All experiments were conducted in the dark and under continuous agitation using a magnetic stirrer in 125 mL capped amber bottles under headspace-free conditions at room temperature (21 ± 1 °C). Reactions were initiated by the injection of an aliquot of a HOCl stock solution to the buffered solutions containing various types of DOM with or without CuO.…”

Phosphate Chemical Use for Sequestration, Scale Inhibition, and Corrosion Control

“…Manufacturers often claim about 0.66–1.33 mg/L polyphosphate as P is sufficient. , For scale inhibition, manufacturers claim approximately 2–4 mg/L hexametaphosphate will inhibit scaling from 200 mg/L hardness (as CaCO 3 ) . However, as little as 0.1 mg/L polyphosphate-P can reduce scaling by 75–95% and 0.1 mg/L orthophosphate-P can reduce scaling by 50%. , …”

“…35 However, as little as 0.1 mg/L polyphosphate-P can reduce scaling by 75− 95% and 0.1 mg/L orthophosphate-P can reduce scaling by 50%. 37,38 Turbidity and Color. Color and turbidity measurements are important tools for characterizing consumer observations of iron and manganese precipitation in potable water distribution.…”

Utility considerations in developing a galvanized iron water pipe management plan

“…Orthophosphate inhibitors may be effective in slowing GIP corrosion by developing a protective scale (Schock et al, 2014). In contrast, polyphosphate inhibitors may increase solubility of Fe complexes or the fraction of colloidal Fe particles (Lytle et al, 2005; McNeill & Edwards, 2001; Wang et al, 2017). In one recent study, adjusting pH to 7.5 and dosing orthophosphate was shown to be more effective in controlling Pb and Fe from GIP compared with other treatment strategies such as silicate or polyphosphate addition for one water system in California (Tang, Nystrom, et al, 2018).…”