Corrosion and its Effects
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Corrosion and its Effects

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Questions and Answers

What is a significant factor that contributes to the corrosion resistance of steel pipelines?

  • Soil composition (correct)
  • Water salinity
  • Temperature variation
  • Pesticide presence

    • Which mechanism of stress corrosion cracking involves hydrogen reducing the strength of steel?

  • Electrolytic Corrosion
  • Anodic Dissolution
  • Hydrogen Embrittlement (correct)
  • Film Rupture

    • In which environment is anodic dissolution most likely to accelerate crack propagation in steel?

  • Temperate forests
  • Freshwater lakes
  • Desert regions
  • Chloride-containing environments (correct)

    • What is the primary cause of crack growth in steel during stress corrosion cracking?

    <p>Combined tensile stress and corrosive environment</p> Signup and view all the answers

    Which of the following statements is true regarding the passive oxide film on steel?

    <p>It can rupture under stress, leading to corrosion.</p> Signup and view all the answers

    What is one major form of external corrosion in steel pipelines?

    <p>Stress corrosion cracking (SCC)</p> Signup and view all the answers

    What essential role do pipelines serve in modern energy?

    <p>Economic and safe transportation of oil and gas</p> Signup and view all the answers

    What can lead to internal corrosion in pipelines?

    <p>Corrosive environments such as CO2, H2S, and bacterial activity</p> Signup and view all the answers

    Which of the following is commonly used for analyzing stress distribution in materials?

    <p>Finite Element Analysis (FEA)</p> Signup and view all the answers

    What happens during the long-term service of buried pipelines?

    <p>The external coating may degrade, leading to corrosion</p> Signup and view all the answers

    What does simulation of stress corrosion cracking help predict?

    <p>Failures in critical infrastructure</p> Signup and view all the answers

    What does the Nernst equation describe in relation to metal ions in a solution?

    <p>The relationship between the electrical potential difference and ion concentration.</p> Signup and view all the answers

    What is represented by the dashed lines in a Pourbaix diagram?

    <p>The reduction reactions for oxygen and hydrogen.</p> Signup and view all the answers

    In what condition will a metal corrode when placed in an environment?

    <p>When its standard potential is more negative than that of the coupled cathodic reaction.</p> Signup and view all the answers

    Which model specifically focuses on crack propagation once a crack has initiated?

    <p>Fracture Mechanics Models</p> Signup and view all the answers

    What does Corrosion Models predict?

    <p>Electrochemical processes leading to corrosion</p> Signup and view all the answers

    In the electrochemical reaction for metal oxidation, what happens to the metal?

    <p>It is converted to its ion form and releases electrons</p> Signup and view all the answers

    What is shown between the dashed lines in a Pourbaix diagram?

    <p>The stability of water across varying potentials and pH.</p> Signup and view all the answers

    What primary mechanism is responsible for the deterioration of metals during corrosion?

    <p>Electrochemical reaction with the environment</p> Signup and view all the answers

    Which component of the Nernst equation accounts for the temperature dependence of the electrochemical potential?

    <p>The gas constant, R.</p> Signup and view all the answers

    What is the role of the electrolyte in the corrosion process?

    <p>To facilitate the electrochemical reactions</p> Signup and view all the answers

    Which of the following reactions represents cathodic oxygen reduction in neutral media?

    <p>$O_2 + 2H_2O + 4e^- ightarrow 4OH$</p> Signup and view all the answers

    What is a significant contributor to the high economic cost of corrosion globally?

    <p>Material replacement costs</p> Signup and view all the answers

    When modeling SCC, which method is utilized to incorporate the effects of elastic and plastic deformation?

    <p>Small strain plasticity model</p> Signup and view all the answers

    What criterion is typically employed in predicting the yielding behavior of materials in SCC modeling?

    <p>Von-Mises yielding criterion</p> Signup and view all the answers

    In the corrosion process, what is observed to occur simultaneously with anodic oxidation?

    <p>Hydrogen evolution as a cathodic reaction</p> Signup and view all the answers

    What does Icorr represent in the equation for estimating corrosion rate?

    <p>The corrosion current density</p> Signup and view all the answers

    Which of the following factors does NOT affect the calculation of Icorr?

    <p>The pH of the solution</p> Signup and view all the answers

    How is the overpotential (η) defined according to the content?

    <p>As the difference between the applied potential and the open circuit potential</p> Signup and view all the answers

    What is the role of Faraday's constant (F) in the corrosion rate equation?

    <p>It relates current to the amount of substance that reacts per unit charge</p> Signup and view all the answers

    What does the intersection of the anodic and cathodic reactions represent in corrosion studies?

    <p>The corrosion current density (icorr)</p> Signup and view all the answers

    In the Butler-Volmer equation, what does the term $i_{corr}$ represent?

    <p>The current density at corrosion conditions</p> Signup and view all the answers

    How does the porosity of soil influence corrosion rates of buried structures?

    <p>It controls the flow of fluids through the soil</p> Signup and view all the answers

    What is indicated by the Tafel slope in corrosion studies?

    <p>The relationship between current density and overpotential</p> Signup and view all the answers

    Study Notes

    Corrosion and its Effects

    • Corrosion is the deterioration of metal due to electrochemical reactions with the environment.
    • The direct cost of metallic corrosion in the United States was estimated to be 3.1% of the U.S. Gross Domestic Product (GDP) in 2002.
    • The global cost of corrosion was estimated to be 3.4% of global GDP in 2013.
    • Corrosion requires a conductive solution (electrolyte), an electronic path, an anodic reaction, and a cathodic reaction.
    • The anodic reaction is the oxidation of the metal.
    • The cathodic reaction is the reduction of an oxidizing agent.
    • The rate of the anodic reaction is equal to the rate of the cathodic reaction.
    • The metal is oxidized to a metal ion while electrons are released and consumed during the reduction reaction.
    • The number of electrons released equals the valence of the metal ions released to the electrolyte.
    • The electrochemical series of metals is formed by listing the standard potentials of different metals in ascending or descending order, taking the standard potential of hydrogen as the zero point.
    • A metal will corrode if its standard potential is more negative than the standard potential of the coupled cathodic reaction.
    • The oxidation reaction can be illustrated using a Pourbaix diagram where the electrochemical potential is plotted vs. the pH of water at 25°C.
    • The Pourbaix diagram can be used to identify the electrochemical state of a metal (immunity, actively corroding, or passivity) at a specific pH and potential.
    • Corrosion rate can be estimated using Faraday's law: Icorr = nFW/MT, where n is the valence of the metal, F is Faraday's constant (96,500 C.mol¯¹), W is the atomic mass of the metal, M is the mass of corroded metal (g), and T is the time the current was applied (s).
    • The potential difference between the corroded metal and a reference electrode is known as the open circuit potential (Eoc) or corrosion potential (Ecorr).
    • Overpotential (n) is the deviation of the potential from Eoc when an external current is applied: n=E-Eoc.
    • The intersection of the anodic and cathodic reactions in a polarization diagram represents the Eoc/Ecorr and icorr.

    Corrosion in Soils

    • Soil porosity controls the flow of fluids through the soil, affecting the corrosion of buried structures.
    • Coarse-grained soils have higher oxygen permeability, while fine-grained soils have higher water saturation.
    • The pH and composition of groundwater in contact with buried structures depends on the soil and climate.
    • Chloride concentration is high in desert regions, making the soil very corrosive.
    • Soils in tropical climates tend to be very acidic.
    • Corrosion resistance of steel pipelines varies depending on soil composition, pH, and moisture content.

    Stress Corrosion Cracking (SCC) in Steel

    • SCC results from a combination of a susceptible material, a specific chemical species (environment), and tensile stress.
    • The mechanism of SCC in steel involves the combined action of tensile stress and a corrosive environment.
    • SCC can occur in various environments such as seawater, acidic solutions, or caustic environments.
    • Common proposed mechanisms for SCC in steel include:
      • Hydrogen embrittlement: Hydrogen diffuses into steel under stress, leading to brittle fracture.
      • Anodic dissolution: Aggressive species can cause anodic dissolution at the crack tip, accelerating crack propagation.
      • Film rupture and repassivation: Rupture of the passive oxide film formed on the surface of some steels under stress, allowing corrosion.

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    Description

    Explore the concept of corrosion and its significant impact on materials and the economy. This quiz delves into electrochemical reactions, the costs associated with corrosion, and the fundamental processes involved. Gain insights into how metals deteriorate and the factors that influence these reactions.

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