Galvanic Lead Corrosion in Potable Water: Mechanisms, Water Quality Impacts, and Practical Implications

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dc.contributor.authorNguyen, Caroline Kimmyen
dc.contributor.committeechairEdwards, Marc A.en
dc.contributor.committeememberScardina, Robert P.en
dc.contributor.committeememberCorcoran, Sean G.en
dc.contributor.committeememberBoardman, Gregory D.en
dc.contributor.departmentCivil Engineeringen
dc.date.accessioned2017-04-06T15:44:02Zen
dc.date.adate2010-11-04en
dc.date.available2017-04-06T15:44:02Zen
dc.date.issued2010-08-27en
dc.date.rdate2016-10-07en
dc.date.sdate2010-10-04en
dc.description.abstractAs stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and copper. If the resulting galvanic current exceeds about 2 µA/cm², a highly corrosive microenvironment can form at the solder surface, with pH <2.5 and chloride concentrations 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface and contributing to lead contamination of potable water. If the concentration of sulfate increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated. Mechanistically, at the relatively high concentrations of lead and low pH values that might be present at lead surfaces, sulfate forms precipitates while chloride forms soluble complexes with lead. Considering net transport of anions in water, a chloride-to-sulfate mass ratio (CSMR) above 0.77 results in more chloride than sulfate transported to the lead anode surface, whereas the converse occurs below this CSMR. Bicarbonate can compete with chloride transport and buffer the pH, providing benefits to lead corrosion. Although orthophosphate is often an effective corrosion inhibitor, tests revealed cases in which orthophosphate increased lead and tin release from simulated soldered joints in potable water. Phosphate tended to increase the current between lead-tin and copper when the water contained less than 10 mg/L SO₄²⁻ or the percentage of the anodic current carried by SO₄²- ions was less than 30%. Additionally, nitrate in the potable water range of 0-10 mg/L N dramatically increased lead leaching from simulated soldered pipe joints. Chloramine decay and the associated conversion of ammonia to nitrate during nitrification could create much higher lead contamination of potable water from solder in some cases. In practical bench-scale studies with water utilities, the CSMR was affected by the coagulant chemical, blending of desalinated seawater, anion exchange, and sodium chloride brine leaks from on-site hypochlorite generators. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead-tin solder connected to copper.en
dc.description.degreePh. D.en
dc.identifier.otheretd-10042010-134402en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-10042010-134402/en
dc.identifier.urihttp://hdl.handle.net/10919/77237en
dc.language.isoen_USen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectchlorideen
dc.subjectGalvanic corrosionen
dc.subjectsulfateen
dc.subjectalkalinityen
dc.titleGalvanic Lead Corrosion in Potable Water: Mechanisms, Water Quality Impacts, and Practical Implicationsen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineCivil Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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