Localized Corrosion -- Measurement, Mechanisms and Mitigation: Assorted Effects
Sponsored by: MS&T Organization
Program Organizers: Gerald Frankel, Ohio State University

Tuesday 8:00 AM
October 18, 2011
Room: D244/245
Location: Greater Columbus Convention Center

Session Chair: Gerald Frankel, The Ohio State University

8:00 AM  
Study of Carbon Steel Corrosion at the Liquid-Air Interface in Simulated Nuclear Waste Solutions: Xiaoji Li1; Feng Gui2; Sean Brossia2; Gerald Frankel1; 1The Ohio State University; 2DNV Columbus, Inc.
    Millions of gallons of high-level radioactive liquid waste are stored in underground carbon steel tanks. Localized corrosion at the liquid-air interface in tanks might endanger their integrity. The mechanism of liquid-air interface corrosion (LAIC) is unknown. Electrochemical measurements were conducted to examine conditions that favor LAIC, in terms of pH, nitrate/nitrite concentration, deaeration and temperature. Gradients of pH, oxygen and nitrate/nitrite concentration across the meniscus as LAIC mechanism were examined. Interestingly, the differential aeration cell theory does not explain the observations of LAIC. Although the meniscus pH decreased as LAIC worsened, it is unclear whether the pH decrease is the cause or effect of LAIC. The air-liquid interface was investigated by sum frequency generation spectroscopy showing a reduced number of free OH- in nitrate solution compared to water with the same pH. In-situ Raman spectroscopy of the meniscus solution and cathodic polarization were also used to address this problem.

8:20 AM  Student
Mitigation of Microbiologically Influenced Corrosion Using High Frequency Ultrasonic Techniques: Hussain Almahamedh1; Douglas Meegan1; Brajendra Mishra1; David Olson1; 1Colorado School of Mines
    Microbiologically Influenced Corrosion (MIC) is a major problem in oil industry facilities, and considerable effort has been spent to mitigate it. The most effective method to control MIC is the use of biocides. However, biocides are expensive and harmful to people and the environment. More environmentally benign methods are under consideration as alternatives to biocides, among which are ultrasonic techniques. In this study, a high frequency ultrasonic (HFUT) technique was used as a mitigation method for MIC. The killing efficacy of this technique on different types of bacteria was investigated. The corrosion of UT-treated and untreated bacteria on API 5L-X52 pipeline steel was evaluated by electrochemical analysis. On all of these bacteria, the killing percentages of the HFUT were higher than 99.8%. The electrochemical analyses reveal a decrease of more than 50% in the corrosion rate of X52 exposed to the HFUT-treated bacteria.

8:40 AM  
Pitting Corrosion of Cu in Various Atmospheric Environments with Ozone and UV Radiation: Huang Lin1; Gerald Frankel1; Mark Jaworowski2; 1Fontana Corrosion Center, The Ohio State University; 2United Technologies Research Center
    Cu was exposed in a laboratory exposure chamber with ozone, UV and various aerosols or surface salt deposits. In the absence of aerosols or salts, the naturally formed thin cuprous oxide layer provided good protection that limited the corrosion rate. However, in the presence of certain aerosols or salt deposits, the atmospheric corrosion rate of Cu dramatically increased, even though the main corrosion products were still cuprous oxide. A large number of small pits initiated during exposure as well as uniform corrosion. The morphology of exposed samples was viewed by SEM and corrosion products were identified by XRD. The pit morphology was analyzed by interferometric optical profiling. It is believed that the presence of aerosols resulted in pit initiation and increase in the corrosion rate. The effects of ozone and UV on pit initiation are being studied.

9:00 AM  
Electropolishing of Niobium to Obtain Defect Free Surface: Ashwini Chandra1; Gerald Frankel1; Michael Sumption1; 1The Ohio State University
    Pure niobium is used for making Superconducting Radio Frequency (SRF) cavities. These cavities need to have a good surface finish to achieve maximum performance. Surface defects like grain boundaries and pits seriously affect their performance. Electropolishing (EP) in hydrofluoric/sulfuric acid is commonly used as a final process to give a good surface finish to the niobium surface. However the optimum EP conditions have not been fully explored. The effect of acid concentration, stirring and temperature is studied using flat niobium specimen. Hydrodynamics is also critical for the surface finish obtained and the effect is analyzed by comparing the surface finish obtained under similar conditions for a well exposed area and a flag electrode. Current oscillation obtained at the end of the current density plateau is studied. The result of electropolishing in different voltage regimes of the polarization curve is compared using topography measurement by AFM and optical profilometer.

9:20 AM  Student
The Influence of Sulfate Reducing Bacteria Metabolic Reactions on the Corrosion Behaviour of API-5L X65 Carbon Steel Pipeline: Faisal AlAbbas1; Arshad Bajvani Gavanluei2; David Olson2; Brajendra Mishra2; Antony Kakpovbia1; John Spear2; Tariq Al-Ghamdi2; 1Saudi Aramco; 2Colorado School of Mines
    Microbiologically influenced corrosion (MIC) by Sulfate Reducing Bacteria (SRB), Desulfovibrio africanus sp, on API-5L grade X65 carbon steel was investigated. The corrosion behavior was characterized by Electrochemical Impedance Spectroscopy (EIS), linear polarization resistance (Rp) and open circuit potential (OCP). EIS spectra displayed one time constants for the sterilized growth media. The time constant was related to a mixture layer of corrosion products with chlorides and organic compounds that precipitated out from the growth media. Conversely, one time constant with a finite Warburg element were observed in the SRB cultured media. The SRB Bio-catalytic activities promote the corrosion rate via formation of biofilm, production of hydrogen sulfide and biotic reduction of phosphates and subsequent formation of iron phosphide. Deeper pits were found along the grain boundaries (GB) and boundary triple points. The extensive attack on the grain boundaries has been related to the fact that bacterial initial attachment occurs on or near the grain boundaries. Corrosion products, biofilm and pitting morphology were characterized by X-ray diffraction and Environmental Scanning Electron Microscopy (ESEM).

9:40 AM Break