Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures

Mattsson, Einar; Fredriksson, Andreas

doi:10.1179/000705968798326037

Cited by 71 publications

(49 citation statements)

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“…The effect of each anion on the stability of the passive film on copper has been widely studied in different environments. 38,41,55 Furthermore, combinations of aggressive anions and inhibiting anions ͓͑SO 4 2− ͔/͓HCO 3 − ͔, 7,9,55,56 ͓Cl − ͔/͓HCO 3 − ͔, 42 and ͓SO 4 2− ͔/͓OH − ͔ 57 ͒ have also been a subject of some studies, and some critical anion ratios have been specified to minimize the pitting problems. 9,36 The mechanism is due to either the buffering capability which prevents local acidity or the formation of a possibly protective basic copper carbonate film, CuCO 3 ͑cupric carbonate͒, Cu͑OH͒ 2 ·CuCO 3 ͑mala-chite͒, Cu͑OH͒ 2 ·2CuCO 3 ͑azurite͒, or any combination of these minerals.…”

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confidence: 99%

“…HCO 3 − is generally considered as a beneficial anion to copper pipes in promoting passivity and inhibiting localized breakdown by aggressive anions. 7 In summary, it is generally agreed that SO 4 2− and Cl − promote the breakdown of passive film, and HCO 3 − is effective in counteracting and promoting passivity. [37][38][39][40][41] However, some research has shown that HCO 3 − can actually induce pitting without the presence of other aggressive anions, 3,[42][43][44] and HCO 3 − increases cuprosolvency.…”

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confidence: 99%

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Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

Cong

Michels

Scully

2009

J. Electrochem. Soc.

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The electrochemical pitting behavior of UNS C11000 copper was investigated in a synthetic potable water found to cause pitting. Tests were also conducted in several other HCO 3 − , SO 4 2− , and Cl − containing waters with systematic variations in concentrations of these species. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method complemented by various diagnostic methods. Certain water chemistry concentrations promote pitting. Critical pitting potentials ͑E Pit ͒ for copper pitting are decreased by certain water chemistry variables. High ͓SO 4 2− ͔/͓OH − ͔, ͓SO 4 2− ͔/͓HCO 3 − ͔, and Cl − /͓HCO 3 − ͔ ratios lower pitting potentials while an increase in alkalinity ͑increasing ͓OH − ͔ or ͓HCO 3 − ͔/͓CO 3 2− ͔͒ improves passivity and raises pitting potentials. HCO 3 − /CO 3 2− can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial toward passivity compared to OH − with respect to passivation efficiency. Empirical equations that forecast pitting and repassivation potentials as a function of selected water chemistry variables were developed by linear regression analysis based on experimental pitting and repassivation potential trends with HCO 3 − , Cl − , and SO 4 2− content. The origins of the trends with water chemistry variables are discussed.

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confidence: 99%

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confidence: 99%

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

Cong

Michels

Scully

2009

J. Electrochem. Soc.

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“…The relationship between pitting corrosion of copper piping and water chemistry has been investigated by many researchers for over half a century. These range from early studies by Campbell (2,3), Lucey (4,5), Cornwell (6), Mattsson (7)(8)(9), and Pourbaix (10,11) to recent researchers (12)(13)(14)(15)(16)(17)(18)(19)(20). Copper pitting has been historically classified into three types: type I (cold water pits), type II (hot water pits) and type III (soft water pits) (15,21).…”

Section: Introductionmentioning

confidence: 96%

“…In contrast, SO 4 2-not only causes active pitting but may be a more potent anion than Cl -since CuSO 4 is very soluble (38,41,55). Furthermore, combinations of aggressive anions and inhibiting anions ([SO 4 2-]/[HCO 3 -] (7,9,55,56), [Cl -]/[HCO 3 -] (42), and [SO 4 2-]/[OH -](57)) have also been a subject of some studies, and some critical anion ratios have been specified to minimize the pitting problems. For example, Mattsson points out that pitting is not likely to occur in hot water tubes of hard copper if the [HCO 3 -]/[SO 4 2-] ratio is ≥ 1 (7).…”

Section: Introductionmentioning

confidence: 99%

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

2009

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The electrochemical pitting behavior of UNS C11000 copper was investigated in a synthetic potable water found to cause pitting. Tests were also conducted in several other HCO3-, SO42- and Cl- containing-waters. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method. Certain water chemistry concentrations promote pitting. High [SO42-]/[OH-],[SO42-]/[HCO3-] and [Cl-]/[HCO3-] ratios lower pitting potentials while an increase in alkalinity improves passivity and raises pitting potentials. HCO3-/CO32- can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial towards passivity compared to OH- with respect to passivation efficiency. Empirical equations that forecast pitting and repassivation potentials as a function of selected water chemistry variables were developed by linear regression analysis based on experimental pitting and repassivation potential trends with HCO3-, Cl- and SO42- content. The origins of the trends with water chemistry variables are discussed.

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“…Pitting corrosion of copper in water has been categorized into at least three types based on water chemistry and physical features: cold-water (Type I) [2,[8][9][10], hot-water (Type II) [11], and soft-water (Type III) [12]. Soft-water copper pits are described as being relatively wide and shallow and consisting of an exterior layer of bronchantite [Cu 4 (SO 4 )(OH) 6 ] and/or malachite [Cu 2 (CO 3 )(OH) 2 ] over a layer of crystalline red-brown cuprite [Cu 2 O] and the corroding copper surface.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

Lytle

White²

2014

J Fail. Anal. and Preven.

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Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended orthopolyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper-phosphorus solids were identified under SEM magnification; however, no crystalline copper-phosphate compound was identified by x-ray diffraction analysis.

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Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures

Cited by 71 publications

References 1 publication

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

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