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Yorba Linda, CA, United States

Kappes M.,Ohio State University | Frankel G.S.,Ohio State University | Sridhar N.,DNV Columbus Inc. | Carranza R.M.,CNEA
Journal of the Electrochemical Society | Year: 2012

Corrosion tests with gaseous H 2S require special facilities with safety features, because H 2S is a toxic and flammable gas. The possibility of replacing H 2S with thiosulfate (S 2O 3 2-), a non-toxic anion, for studying stress corrosion cracking of stainless and carbon steels in H 2S solutions was first proposed by Tsujikawa in 1993. H 2S production was detected in presence of carbon steel corroding in acidified thiosulfate-containing solutions. In this paper, the kinetics of H 2S evolution are used to estimate the range of partial pressure of H 2S that can be simulated with thiosulfate solutions. It was determined that acid brines containing 10 -4 M and 10 -3 M S 2O 3 2- could be used for replacing continuous bubbling of dilute H 2SN 2 mixtures in tests of degradation of carbon steels, with H 2S partial pressures ranging between 0.03 and 0.56 kPa. The kinetics of H 2S production were compared with the amount of sulfur in side reactions, like formation of iron sulfide films and elemental sulfur. © 2012 The Electrochemical Society.

Daily S.F.,DNV Columbus Inc.
NACE - International Corrosion Conference Series | Year: 2011

Degradation of buried metallic piping is a significant issue facing owners and operators of nuclear power plants. The piping at nuclear plants consists of a network of different materials that are interconnected through the station ground to reduce the effects of hazardous voltages associated with lightning and fault currents in the earth. By connecting the metallic piping to the copper grounding grid, corrosion rates can increase on some of the buried piping resulting in loss of metal and reduction in wall thickness. When cathodic protection (CP) is applied at nuclear power plants to control corrosion of the buried piping, much of the current will tend to flow to other metallic structures that are not intended for CP. This will result in a significant increase in the current requirement for cathodic protection. The design of the CP systems is further complicated by the complex configuration of the piping networks, limited space and shielding effects from building foundations and other buried structures. This paper discusses the issues associated with the design and installation of CP systems for buried nuclear piping; taking into account the need for higher current requirements, uniform current distribution, anode bed configuration, test sites and criteria for effective cathodic protection. ©2011 by NACE International.

Cong H.,University of Virginia | Scully J.R.,University of Virginia | Scully J.R.,DNV Columbus Inc.
Journal of the Electrochemical Society | Year: 2010

Natural pitting was investigated using coupled multielectrode arrays (CMEAs) constructed from flush mounted, close-packed UNS C11000 copper wires exposed in chlorinated and aerated Edwards synthetic drinking waters (ESDWs) [J. C. Rushing and M. Edwards, Corros. Sci., 46, 3069 (2004)]. Tests were conducted in ESDWs with pH adjusted from 6 to 10 and containing 5 ppm Cl2. The CMEA method detected the formation of persistent anodes (pitting) in pH7 synthetic waters compared to switchable anodes at pH≥6 (uniform corrosion). Local maximum and minimum open-circuit potentials (OCPs) were analyzed before, during, and after pitting events and were compared to pitting (Epit) and repassivation (Erp) potentials. Natural pitting was found to occur on a small percentage of electrodes once the OCP rose above Erp determined in upward/downward scans. Pits stopped growing once the OCP dropped below Erp. Pitting factors, determined as a function of pH, increased with pH from 7 to 9. However, a further increase in pH to 10 reduced pitting, which could not be determined from other test methods. This drop in pitting factor could be ascertained from arrays but not from a comparison of OCPs to pitting potentials seen in upward scans. The cathodic capacity of adjacent cathodic sites as a function of water chemistry and the nature of the cathodic sites were factored into this analysis. © 2009 The Electrochemical Society.

Cong H.,University of Virginia | Cong H.,DNV Columbus Inc. | Scully J.R.,University of Virginia
Journal of the Electrochemical Society | Year: 2010

The cathodic reduction reaction kinetics of free chlorine and oxygen on UNS C11000 copper microelectrodes were investigated in Edwards synthetic drinking water. OCl- increases cathodic reaction rates and thus raises open-circuit potential (OCP) toward pitting potentials. An increase in both the mass-transport factor K (where ilim =K ω1/2) for chlorine reduction (HOCl and OCl-) and OCP was observed as pH was increased from 8.5 to 9.5, and free chlorine levels were raised. Natural pitting was investigated using coupled multielectrode copper (UNS C11000) arrays exposed under the same conditions from pH 6 to 10 with various residual free chlorine concentrations (0-5 ppm). An empirical equation that forecasts the OCP as a function of pH and Cl2 concentration was developed. This enabled an assessment of the pitting susceptibility of various waters based on the comparison of OCPs to critical pitting potentials. Pits formed when the OCP rose above repassivation potential Erp and stopped growing once the OCP dropped below Erp. Pitting severity, as determined by calculated pitting factors, increased with free chlorine concentration and was highest at pH 9. © 2010 The Electrochemical Society.

Tossey B.,DNV Columbus Inc.
Power Engineering (Barrington, Illinois) | Year: 2011

DNV Columbus Inc., (DNV) was contracted by a utility to investigate the cause of internal corrosion in wet flue gas desulfurization (WFGD) absorbers. The absorbers were in service for approximately 12 to 18 months before through-wall pinhole leaks were found during regular external visual inspections of the shell. Scale samples and surface swabs were collected by the company's engineers for laboratory analysis and preservation. The company analyzed the scales using x-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) to determine the composition and crystal structure of the scales. A representative photograph of a horizontal weld seam revealed black and red colored scale attached to the tank wall with tan deposits partially covering the black and red scale. EDS and XRD analysis of the black scale showed it contained manganese, fluoride, silicon, aluminum, calcium, sulfur, oxygen, and iron.

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