Showing papers in "Corrosion in 1994"

Transgranular Stress Corrosion Cracking of High-Pressure Pipelines in Contact with Solutions of Near Neutral pH

Abstract: Although intergranular stress corrosion cracking (IGSCC) of high-pressure gas pipelines has been known for more than 20 years, a transgranular form (TGSCC) was detected more recently. Inst...

Lifetime Prediction for Organic Coatings on Steel and a Magnesium Alloy Using Electrochemical Impedance Methods

Abstract: Electrochemical impedance studies were conducted on an epoxy polyamide-coated AISI1010 steel (UNS G10100) and an epoxy/chromate conversion-coated magnesium (Mg) alloy ZE41A-T5 (UNS M16410)...

Electrochemical Behavior of the T1 (Al2CuLi) Intermetallic Compound and Its Role in Localized Corrosion of Al-2% Li-3% Cu Alloys

Abstract: The T1, (Al2CuLi) intermetallic compound was synthesized in bulk form for characterization of its electrochemical behavior in chloride solutions by conventional direct current (DC) techniques. Results indicated T1, was active with respect to its microstructural suroundings in artificially aged Aluminum Association (AA) 2090 (UNS A92090) (Al 2.1% Li-2.6% Cu) and preferential dissolution of T1 precipitates strongly influenced localized corrosion behavior of the alloy. Subgrain boundaries in artificially aged AA 2090 were particularly susceptible to localized attack because of high concentrations of T1. The role of T1, in preferential subgrain boundary attack in a chloride-free sulfate solution also was investigated.

Performance of Black, Galvanized, and Epoxy-Coated Reinforcing Steels in Chloride-Contaminated Concrete

Abstract: The corrosion performance of black steel, galvanized steel, and epoxy-coated steel in concrete was investigated. Samples were exposed to cyclic salt water wetting and drying or to a contin...

Carbon Dioxide Corrosion of Carbon Steel in Two-Phase Flow

Abstract: Results were presented from a four-year experimental study on carbon dioxide (CO2) corrosion of carbon (C) steel in two-phase flow. Tests were carried out in a gas and water loop that permitted control and regulation of relevant parameters. Flow rates of gas and water were regulated independently to obtain a number of two-phase flow regimes, such as bubble flow and slug flow. In more than 20 long-term experiments lasting from one to several weeks each, pH was varied from 4 to 7 while the temperature was held at 20°C, 40°C, 60°C, and 80°C in different experiments. Corrosion rates were monitored continuously in time with a radiation detection technique. Scanning electron microscopy analysis and x-ray analysis of the specimen surface and cross section were done on selected specimens after each experiment. It was found that, in cases where the formation of protective films is difficult, flow could have a “positive” role by eroding the iron carbide films that otherwise would accelerate corrosion by ga...

Use of Mössbauer Spectroscopy to Study Reaction Products of Polyphenols and Iron Compounds

Abstract: Mossbauer spectroscopy was used to study parameters of the reaction products of iron compounds (FeIII) and polyphenols with hydroxyl (OH) groups in ortho positions. Polyphenols used in the...

Corrosion-Resistant, Chromate-Free Talc Coatings for Aluminum

Abstract: Aluminum (Al) and Al alloys exhibit unusual passivity when immersed in alkaline lithium (Li) salt solutions. This passivity is a result of precipitation of a continuous, polycrystalline talc coating. Talc coatings persist when removed from the Li salt solution and offer increased corrosion protection during exposure to aggressive environments. Efforts to develop a low-cost, low-toxicity, easily applied corrosion-resistant coating for Al are ongoing. Surface analytical and electrochemical experiments aimed at characterizing the structure, composition, and barrier properties of talc coatings were conducted. The solution chemistry involved in talc formation was studied, and the conditions under which coatings form readily were established. Results showed coatings formed by immersion in an alkaline Li salt bath followed by a low-temperature (≤ 100°C) heat treatment in air or water provided barrier properties that compared favorably with those of traditional inorganic corrosion-resistant coatings, suc...

Crevice Corrosion of Alloy 625 in Chlorinated ASTM Artificial Ocean Water

Abstract: Factors controlling the initiation and propagation of crevice corrosion on alloy 625 (UNS N06625) in ocean water of ambient temperature were explored within the contexts of the Oldfield-Sutton model for critical crevice corrosion solution (CCS) development and the ohmic criterion for crevice corrosion initiation. Data supported an earlier claim that a critical potential drop must be exceeded to initiate crevice corrosion. Steady-state crevice corrosion propagation was found to be under ohmic control. Chlorine decreased the time required for initiation and possibly raised propagation rates in ASTM artificial ocean water. Addition of molybdate (MoO42−) to ocean water (simulating the dissolution of alloyed molybdenum [Mo]) delayed initiation and reduced propagation rates temporarily, but not sufficiently to explain fully the inhibiting effects of alloyed Mo. Beneficial effects on crevice corrosion susceptibility of alloyed Mo and equivalent chromium (Creq) concentration were examined critically in t...

Pitting Corrosion of Pipeline Steel in Dilute Bicarbonate Solution with Chloride Ions

Abstract: Corrosion behavior of grade 550 (X-80) pipeline steel with coating disbondments was studied in a range of bicarbonate (HCO3−) solutions using a potentiodynamic polarization technique. Corrosion morphology of the steel was examined using optical and scanning electron microscopy. The shape of the polarization curves and the sensitivity of the steel to pitting corrosion varied with HCO3− concentration. Increases in HCO3− concentration resulted in a wider passive region and a more noble breakdown potential (Eb), resulting in greater resistance to pitting corrosion. Surface morphology showed no pit formation in solutions with HCO3− concentration > 0.05 M, but pits developed at a concentration of 0.05 M. Size and density of corrosion pits increased with further decreases in HCO3− concentration. The graph of corrosion potential (Ecorr) vs HCO3− concentration showed a peak at 0.05 M, whereas the corrosion current density increased monotonically with increased HCO3− concentration. Low concentrations of ch...

A Numerical Model for Cathodic Protection of Buried Pipes

Abstract: A mathematical modeling of large, cathodically protected, buried pipe networks was undertaken. The resulting model, OKAPPI, an abbreviation for the Dutch “Ondergrondse Kathodische Protectie Pijpleidingen,” coupled the boundary element method (BEM) and the finite element method (FEM) for the cathodic protection of buried pipes. The approach was based on the assumption that the soil was homogeneous, and the local earth surface was presumed flat. The current density pattern around the pipes was modeled as uniform. The model was three dimensional and minimized discretization. The major innovation in the simulation was the inclusion of nonnegligible ohmic voltage drops in the pipelines. OKAPPI results were shown to simplify macroscopic design since knowledge of potential levels along pipes, potential distribution in the soil, axial currents flowing through pipelines, and radial current densities leaving or entering the pipe walls is important for the monitoring and control of cathodic protection syste...

Computation of Reinforcing Steel Corrosion Distribution in Concrete Marine Bridge Substructures

Abstract: Corrosion conditions prevalent in the partially submerged, reinforced concrete substructures of marine bridges were incorporated into a computer model. The modeled system was an axisymmetr...

Electrochemical Impedance Spectroscopy of Coated Aluminum Beverage Containers: Part 1 Determination of an Optimal Parameter for Large Sample Evaluation

Abstract: Future environmental regulations will limit the volatile organic content of many coatings, including those used on the internal walls of aluminum (Al) cans. Thus, the coating industry is i...

Hydrogen Embrittlement of Cathodically Protected High-Strength, Low-Alloy Steels Exposed to Sulfate-Reducing Bacteria

Abstract: Hydrogen embrittlement (HE) of two high-strength, low-alloy steels was studied in conditions typical of the marine environment. Double-cantilever beam specimens, heat-treated to produce th...

Cathodic protection to mitigate external corrosion of underground steel pipe beneath disbonded coating

Abstract: A study was conducted to determine the feasibility of cathodically protecting the steel surface beneath a disbonded coating with a holiday using an external power source. A laboratory cell...

Degradation of Epoxy Coatings on Phosphatized Zinc-Electroplated Steel

Abstract: The corrosion behavior of phosphatized zinc (Zn)-electroplated steel coated with epoxy films of different thicknesses was studied using electrochemical impedance spectroscopy (EIS), the br...

Predicting chloride profiles in concrete

Abstract: Laboratory studies were undertaken to compare chloride (Cl−) profile data to predictions obtained using ASTM C 1202 of Cl− diffusion into concrete. The effective diffusion coefficients (Deff) derived can be used to determine long-term Cl− profiles of concrete structures. Equations relating Deff with resistivity and permeability of concrete were developed. One- and two- dimensional models were used to determine Cl− profiles of Cl− ions entering concrete in structures such as square piles and decks.

Effect of applied potential on changes in solution chemistry inside crevices on type 304L stainless steel and Alloy 825

Abstract: Changes in pH, chloride (Cl−) concentration, and potential inside a rectangular crevice of metal against polymethyl methacrylate (PMMA) were monitored using microelectrodes as a function o...

A Study of the Growth of α-Al2O3 Scales Using High-Resolution Imaging Secondary Ion Mass Spectrometry

Abstract: The oxide morphology and transport processes occurring during the growth of α-aluminum oxide (α-Al2O3) at 1,200°C on an iron-aluminum (Fe-25 wt% Al) alloy and a nickel-aluminum (Ni-32 wt% ...

Corrosion Inhibition of Steel by Bacteria

Abstract: Mild steel was exposed to Pseudomonas sp. S9 or Serratia marcescens in synthetic seawater. An increase in corrosion resistance over that in natural seawater was monitored by electrochemical techniques. Biological analyses were performed to characterize the system. The inhibition effect also was observed when mild steel was coated with bacteria and then immersed in synthetic seawater. When specimens coated with bacteria were transferred to a natural seawater flow system, the inhibition effect disappeared during the first 2 weeks.

Determination of the Reactive Area of Organic Coated Metals Using the Breakpoint Method

Abstract: Experimental results and mathematical considerations were used to investigate the physical meaning and the application limits of the breakpoint method to evaluate the reactive area in organic coatings. The physical meaning of the reactive area values of a metal under an organic coating, obtained using the breakpoint method, were reviewed. Experimental evidence indicated the area was related to coating defects and porosity, rather than to the total reactive or delaminated area. Limits in applying the breakpoint method were reviewed using mathematical considerations that showed the method was not accurate when values of the coating capacitance and double-layer capacitance were too close, which was a possibility during the initial time of degradation and also when two time constants were distinguishable.

Corrosion Behavior of As-Cast, Silicon Carbide Particulate-Aluminum Alloy Metal-Matrix Composites

Abstract: Corrosion characteristics of as-cast, silicon carbide particulate-aluminum (Al) alloy A356 (SiCp-A356 [UNS A13560]) were examined in chloride (Cl−) media using optical and scanning electro...

Structure of Rust on Weathering Steel in Rural and Industrial Environments

Abstract: Rust on weathering steels exposed for up to 11 y in industrial and rural environments exhibited a spotty, nonuniform appearance as a result of contrast between light and dark areas on the surface. The area of the lighter regions increased with exposure time, as well as with increasing alloy content. Microscopic examination of cross sections revealed the dark regions had a porous appearance. The lighter regions were similar except for the presence of a relatively thin, smooth outer-surface layer. Raman spectroscopy indicated the dark, porous rust was comprised of goethite and lepidocrocite, while the smooth outer layer on the light areas was composed of hematite (α-Fe2O3) and magnetite (Fe3O4). Electrochemical potential measurements indicated the lighter areas were more passive. Results suggested formation of the thin outer layer of α-Fe2O3 and Fe3O4 is an important part of the mechanism of protective rust formation on weathering steels in the environments studied.

Corrosion of Carbon Steels, Stainless Steels, and Titanium in Aqueous Lithium Bromide Solution

Abstract: Effects of lithium bromide (LiBr) concentration, pH, temperature, exposure time, and the action of some inhibitors on corrosion of several carbon (C) steels, stainless steels (SS), and a titanium (Ti) alloy were studied. Corrosion rates were determined by the polarization resistance method and compared to rates determined by weight-loss measurements. Pitting potentials (Ep) were evaluated in neutral LiBr solution and with different inhibitors. Pit density and average pit depth depended on the metal tested, with lowest values for Ti, the next lowest values for type 316 SS (UNS S31600), and the highest values for UNS G41350 tempered steel.

Inorganic Anions and Copper Pitting

Abstract: Copper (Cu) pitting was examined in oxygenated solutions containing bicarbonate (HCO3−), chloride (Cl−), nitrate (NO3−), perchlorate (ClO4−), or sulfate (SO42−) ions at pH values of 5.5, 7.0, 8.5, and 10.0. While short-term (a few hours) cyclic polarization experiments at anion concentrations (or ionic strengths) typical of drinking waters were inconclusive, potentiostatic testing provided insight into Cu pitting behavior. Cl− exhibited a time-dependent dual nature, accelerating anodic reactions in the short term and causing passivation over longer periods. Passivation occurred only at pH 10.0 in the systems containing NO3− and ClO4− and did not occur in the presence of SO42−. Results supported the notion that SO42− or NO3− and not Cl−, (as commonly believed), are key to Cu pitting in potable water distribution systems.

Developments in the slip-dissolution model of stress corrosion cracking

Abstract: Stress corrosion crack growth by slip-dissolution was considered from the standpoint of electrolyte resistance and/or dissolved metal ion concentration in the crack, using a trapezoidal mo...

Sensitization of High-Nitrogen Austenitic Stainless Steels by Dichromium Nitride Precipitation

Abstract: High-nitrogen (N) stainless steels (SS) are receiving increased attention because of their strength advantages over carbon (C)-alloyed materials, but they have been found susceptible to dichromium nitride (Cr2N) precipitation during thermal exposure between ∼ 600°C and 1,050°C. Sensitization susceptibility of a high-N, low-C austenitic SS by Cr2N precipitation at 700°C and 900°C was determined using the single-loop electrochemical potentiokinetic reactivation (EPR) test. High-N SS was found susceptible to sensitization caused by grain boundary (GB) precipitation of Cr2N, with the degree of sensitization increasing systematically with aging time at 700°C. Sensitization of high-N materials did not require the concomitant precipitation of chromium (Cr)-rich metal carbide (M23C6). Materials aged at 900°C were not sensitized, although the rate of precipitation was greater than at 700°C. This indicated the minimum Cr level in the Cr-depleted zone of the matrix associated with nitride precipitation at 9...

Pitting and Crevice Corrosion of Iron Aluminides in a Mild Acid-Chloride Solution

Abstract: Aqueous corrosion (pitting and crevice) characteristics of iron aluminides in a mild acid-chloride (Cl−) solution (200 ppm Cl− [5.5 × 10−3 M sodium chloride {NaCl}] at pH 4 [6.25 × 10−5 M sulfuric acid {H2SO4}]) were studied as functions of alloying additions and thermomechanical processing methods. Electrochemical results indicated beneficial effects of chromium (Cr) and molybdenum (Mo). Immersion tests confirmed the electrochemical results and revealed the time dependence of localized corrosion behavior. The crevice corrosion behavior of iron aluminides was investigated using electrochemical and immersion crevice tests. The difference between crevice and pitting susceptibilities was minimal for the Mo-containing iron aluminide but significant for the iron aluminides without Mo. X-ray photoelectron spectroscopy (XPS) of surfaces passivated in the mild acid-chloride solution revealed the passive films of iron aluminides were composed mainly of oxidized aluminum (Al2O3) that coexisted with chromiu...

Inhibition of Hydrogen Absorption by Steels in Wet Hydrogen Sulfide Refinery Environments

Abstract: Hydrogen permeation and polarization measurements were used to investigate hydrogen absorption by pressure vessel steels in refinery environments containing hydrogen sulfide (H2S), ammonia (NH3), and cyanide (CN−). The severity of these environments is determined by the concentrations of bisulfide (HS−) and CN−. Corrosion rates and hydrogen absorption efficiencies were found to depend on H2S and NH3 concentration in the pH region where HS− was the dominant protonic species. Effects of chemical additives on corrosion and hydrogen absorption were examined. Of the chemicals tested, diamines with long carbon (C) chains were the most effective in reducing the corrosion rate and hydrogen absorption.

Distribution of steady-state cathodic currents underneath a disbonded coating

Abstract: Pipeline corrosion frequently persists underneath disbonded coatings on pipelines that appear to be well protected cathodically. Application of higher cathodic potentials for improved prot...

Inhibition of Copper Corrosion in Aqueous Sodium Chloride Solution by Various Forms of the Piperidine Moiety

Abstract: The inhibition of copper (Cu) corrosion in 1.5% sodium chloride (NaCl) solution was studied in the presence of different concentrations of piperidine, piperidine dithiocarbamate, and its C...