Effect of Chlorine Concentration on Natural Pitting of Copper as a Function of Water Chemistry

Cong, Hongbo; Scully, John R.

doi:10.1149/1.3337005

Cited by 31 publications

(42 citation statements)

References 33 publications

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“…Using CMEAs in relatively short-term experiments, Cong and Scully determined that chlorine levels as low as 1 mg/L could cause copper pitting (as indicated electrochemically) in a similar water quality as that used in the present work (i.e., control water with aluminum solids added); at lower pH, more chlorine was required to induce pitting [21]. They also showed that pitting severity (based on a computed "pitting factor" and maximum total anodic charge) increased with chlorine concentration, which may have been partially related to the short duration of the experiments (6 days) or the near stagnant conditions (i.e., chlorine levels depleted more rapidly at copper surface for low chlorine residual tests).…”

Section: Free Chlorinementioning

confidence: 71%

Inhibition of Copper Pitting Corrosion in Aggressive Potable Waters

Sarver

Edwards

2012

International Journal of Corrosion

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Copper pitting corrosion can lead to premature plumbing failures, and can be caused by aggressive potable waters characterized by high pH, free chlorine residual and low alkalinity. In such waters and under continuous flow, certain inhibitors including phosphate, silica or natural organic matter may greatly reduce pitting occurrence. In the current work, 1 mg/L phosphate (as P) completely prevented initiation of pits, and 5 mg/L silica (as Si) significantly decelerated pitting. However, much lower doses of these inhibitors had little benefit and actually accelerated the rate of attack in some cases. Effects of organic matter were dependent on both the type (e.g., natural versus ozonated humic substances) and dosage. Dose-response effects of free chlorine and alkalinity were also investigated. Based on electrochemical data, pits initiated more rapidly with increased free chlorine, but even moderate levels of chlorine (∼0.4 mg/L) eventually caused severe pitting. High alkalinity decreased pit propagation rates but did not prevent pit formation.

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Section: Free Chlorinementioning

confidence: 71%

Inhibition of Copper Pitting Corrosion in Aggressive Potable Waters

Sarver

Edwards

2012

International Journal of Corrosion

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“…Non-uniform corrosion of copper and copper alloys exposed to flow in this type of water has been confirmed by other researchers. [27][28][29][30] Water was synthesized from reagent-grade chemicals and deionized water to obtain the following quality: pH 9.2, 34 mg/L alkalinity (as CaCO 3 ), 13 mg/L SO 4 2− , 20 mg/L Cl − , 17 mg/L Ca 2+ , and 16 mg/L Na + . This served as a "base" water, which was amended in specific experiments (Table II).…”

Section: Methodsmentioning

confidence: 99%

Flow Electrification and Non-Uniform Corrosion in Low Conductivity Potable Waters

Sarver

Slabaugh

Strock³

et al. 2016

J. Electrochem. Soc.

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"Flow electrification" occurs whenever a fluid passes along a charged surface, creating an electrokinetic "streaming current" or "streaming potential' and is known to cause non-uniform corrosion (and other) problems in non-aqueous fluids. After observing unusual corrosion failures of copper in relatively low conductivity (≈150 μS/cm) potable water, a series of laboratory studies was conducted that verified flow electrification could also develop in aqueous systems and contribute to non-uniform corrosion. Relatively high direct streaming currents along pipelines were quantified in model systems with plastic dielectrics, which accelerated corrosion on the affected pipe section by up to 0.5 μA/cm 2 (assuming uniform corrosion). Very rapid non-uniform pipe failures (i.e., full wall penetration in 7 months) occurred in a system without dielectrics simulating a potable water recirculation system. The effects of flow electrification were virtually eliminated by addition of low levels of zinc phosphate, an inhibitor used in approximate 25% of potable water distribution systems. Flow electrification was also observed in plastic pipe systems with brass connectors. "Flow electrification" is a macroscopic manifestation of electrokinetic "streaming current" or "streaming potential," which develops whenever a fluid passes across a charged liquid-surface interface. Flow electrification of pipelines has been studied extensively over the last century in the petroleum industry, where explosion hazards and pipeline corrosion damage may result when very high voltages are generated via fluid flow in metallic pipes.1-4 Prior reports of flow electrification problems are limited to cases where the involved fluids have low electrical conductivity (e.g., non-aqueous fluids). Thus, for relatively higher conductivity fluids, such as potable water, consequences of flow electrification have largely been assumed irrelevant -although, the phenomenon has been considered theoretically 5 and practically 6-10 as summarized in Table I. Over the course of a decade of research into non-uniform corrosion of copper and dealloying-related failures of brass plumbing components in potable water systems, some practical observations of field failures could not be explained by conventional interpretations. In these cases, non-uniform pitting corrosion and failures were concentrated on the first pieces or sections of metal in the flow sequence, while identical materials downstream suffered no degradation even though they were exposed to identical flows (e.g., same pipe diameter, flow velocity and flow rate). Velocities in the pipes were well-below thresholds at which copper erosion corrosion is a concern (i.e., < 1.2-1.8 m/s), and many of the systems were parts of potable water recirculating systems with a break in electrical continuity at the hot water heater. Similar observations of non-uniform corrosion concentrated on the front portion of copper pipes in a flow sequence were also made during laboratory experiments designed to replicate the failures observ...

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“…One is a 5 × 20 MEA with a 25.4 mm cylindrical epoxy encasing, constructed from 150 μm diameter copper wires (UNS C11000) as described in detail elsewhere. 7,23 The other is a 5 × 20 MEA with a 25.4 mm (1 in) cylindrical copper encasing, mainly used in the Delrin crevice former study. Copper encasing was used to obtain a large covered metal area/crevice volume ratio.…”

Section: Methodsmentioning

confidence: 99%

“…6 Research has demonstrated that pitting corrosion of copper occurs in susceptible waters without aluminum solids. 7,8 However, the presence of aluminum solids increases the likelihood of pitting corrosion in certain water chemistries. 3,9,10 For instance, Edwards et al demonstrated that a synergistic reaction between free residual chlorine (5 ppm Cl 2 ) and aluminum solids (2 ppm Al-Al(OH) 3 ), created particularly aggressive pitting conditions for copper piping at the open circuit potential (OCP) in high pH (pH 9) potable water, based on a synthetic water recipe from Washington Suburban Sanitary Commission (WSSC).…”

mentioning

confidence: 99%

Effects of Aluminum Solids on the under Deposit Corrosion of Copper in Synthetic Potable Water: The Arguments for and against a Semi-Permeable Membrane

Cong

Scully

2013

J. Electrochem. Soc.

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Aluminum solids promote under deposit pitting of UNS C11000 copper. The possible roles that aluminum solids (i.e., Al(OH) 3 ) play to promote copper pitting were examined by various characterization methods followed by diagnostic chemical/electrochemical methods in Edwards synthetic drinking water (ESDW). Cathodic polarization scans indicated that aluminum solids did not affect the intrinsic cathodic half-cell kinetics on an isolated copper electrode. Cyclic potentiodynamic polarization (CPP) experiments showed that the pitting potential (E Pit ) of copper was decreased by the presence of gelatinous aluminum solids deposited on the surface. Multi-electrode arrays (MEAs) with various surface deposition treatments were tested in ESDW under both driven and natural conditions. Lower pitting potentials were found under driven conditions on copper electrodes containing aluminum deposits. Pitting events also occurred on copper electrodes containing aluminum deposits with the presence of 5 ppm Cl 2 under freely corroding conditions. MEAs were also tested with an inert Delrin crevice former. In this case, a lower E Pit and greater number of pitting events were found outside the crevice former. The drop in E Pit was not as severe as in the case of deposited Al(OH) 3 , pointing to effects besides geometrically occluded sites, produced by inert crevice formers. Preferential sorption/transport of selected anions (OH − , HCO 3 − , SO 4 2− , and Cl − ) through gelatinous Al(OH) 3 was studied. Plausible explanations for the detrimental effects of Al(OH) 3 were given.

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Effect of Chlorine Concentration on Natural Pitting of Copper as a Function of Water Chemistry

Cited by 31 publications

References 33 publications

Inhibition of Copper Pitting Corrosion in Aggressive Potable Waters

Inhibition of Copper Pitting Corrosion in Aggressive Potable Waters

Flow Electrification and Non-Uniform Corrosion in Low Conductivity Potable Waters

Effects of Aluminum Solids on the under Deposit Corrosion of Copper in Synthetic Potable Water: The Arguments for and against a Semi-Permeable Membrane

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