(b) With a neat sketch, show how the stray currents from an anode to protect · a structure can cause corrosion of adjace
Set No. 1
Code No: RR410806
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IV B.Tech I Semester Supplimentary Examinations, May/Jun 2009 CORROSION ENGINEERING (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Calculate the half cell potential of hydrogen electrode in a solution of pH = 7 and partial pressure of H2 = 0.5 atm at 40o C.
i. What is the emf of the cell made up of copper electrode and hydrogen electrode (PH2 = 2 atm.) in Copper Sulfate (activity Cu++ = 1) of pH = 1. ii. What is the polarity of the cell and which electrode is anode? [4+8+4]
2. Write short notes on (a) Galvanic corrosion
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(b) Polarization
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(c)
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(b) Calculate the theoretical tendency of Nickel to corrode (in Volts) in deaerated water of pH=7. Assume corrosion products are H2 and N i(OH)2 the solubility product of which is 1.6 × 10−16 .
(c) Cathodic corrosion.
[5+6+5]
3. (a) Give an account of the influence of initial weather conditions on atmospheric/uniform corrosion of steel, zinc and copper in India, U.S and London. (b) Draw isocorrosion charts for steel and lead in sulphuric acid.
[8+8]
4. (a) What is selective leaching in corrosion phenomenon? Give two examples?
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(b) Discuss the most widely accepted mechanism of dezincification process. (c) How will you prevent dezincification?
[8+4+4]
5. (a) Describe the effect of temperature on corrosion.
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(b) Explain about temperature control and testing method for heating tubes. (c) What are the factors to be considered while writing rate expression. [4+8+4]
6. (a) Discuss the principles of anodic protection. (b) With a neat sketch, show how the stray currents from an anode to protect a structure can cause corrosion of adjacent structures? Suggest a method to prevent this problem. [8+8]
7. (a) Explain: Reference electrode, standard electrode potential. (b) Discuss potential pH diagram giving it applications and limitations.
1 of 2
[8+8]
Set No. 1
Code No: RR410806
8. Explain the thermodynamics and kinetics principles involved in the study of electrochemical corrosion. [16]
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Set No. 2
Code No: RR410806
1. (a) Discuss, in detail, about emf series and galvanic series.
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IV B.Tech I Semester Supplimentary Examinations, May/Jun 2009 CORROSION ENGINEERING (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆
[8+8]
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(b) Explain the effect of different environmental variable on corrosion. 2. (a) State why ?
i. Why it is not always safe to couple metals close together in electromotive series ? ii. Why would a unit operating at considerable temperature gradients be subject to severe corrosion? [8+8]
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(b)
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i. Iron functions as a sacrificial anode when coupled with Nickel. ii. Buried Ferrous pipelines buried in wet Carbonaceous backfill have a short life? iii. Grain boundary regions are susceptible to corrosion attack leading to catastrophic structural failure? iv. Head of a nail suffers more corrosion than its shank ?
3. (a) Indicate two criteria for uniform corrosion to take place. (b) Mention two common examples for uniform corrosion. (c) Graphically explain effect of relative humidity and various impurities on rusting of iron. [4+4+8]
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4. (a) Indicate the characteristic property for the following parameters towards SCC shown by an alloy : Temperature increase Crack morphology Presence or absence of corrosion product in the crack Crack surface appearance Stress level -
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i. ii. iii. iv. v.
(b) Schematically represent the effect of simultaneous tensile stress, susceptible metallurgical condition , and critical corrosive solution required for stress corrosion cracking. (c) Discuss graphically rate of SCC propagation as a function of crack depth and specimen extension as a function of time during constant-load stress-corrosion cracking test [5+5+6]
5. (a) Describe the effect of temperature on corrosion. 1 of 2
Set No. 2
Code No: RR410806
(b) Explain about temperature control and testing method for heating tubes. (c) What are the factors to be considered while writing rate expression. [4+8+4] 6. Why are the following important in an anodic protection process (a) active-passive transition of a metal
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(b) potentiostat (c) critical current density.
[5+6+5]
7. Explain the mechanisms of growth and breakdown of passive films.
[16]
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8. Discuss the application of mixed potential theory in estimating the corrosion behaviour of alloys. [16]
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Set No. 3
Code No: RR410806
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IV B.Tech I Semester Supplimentary Examinations, May/Jun 2009 CORROSION ENGINEERING (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) The standard free energies of N aaq+ and P baq4+ are 62.6 and -197 kCal/mole respectively. Calculate E o for Na/N a+ and Pb/P b4+ reactions.
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(b) Obtain an expression for variation of electrode potential of Oxygen electrode with pH at 1 atm.
(c) The corrosion rate of iron in deaerated HCl of pH = 3 is 30 mdd. Calculate the corrosion potential of iron in this acid vs 0.1 N calomel electrode.[8+4+4]
3. (a) Indicate the special name for the atmospheric corrosion of the following metal/alloy. Iron and iron base alloy Copper and Copper base alloy Nickel and Nickel base alloy Silver and Silver base alloy
(b) Furnish isocorrosion charts for Dur iron in sulphuric and nitric acids.
[8+8]
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4. (a) How cavitation corrosion is caused? Schematically represent steps involved in cavitation corrosion. (b) Describe any four methods to combat cavitation corrosion.
[8+8]
5. (a) Describe the effect of temperature on corrosion.
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(b) Explain about temperature control and testing method for heating tubes. (c) What are the factors to be considered while writing rate expression. [4+8+4]
6. Explain the significance of the following design rules: (a) Avoid heterogeneity
(b) Exclude air (c) Avoid excessive vibration (d) Avoid electrical contact between dissimilar metals.
1 of 2
[4×4=16]
Set No. 3
Code No: RR410806
7. (a) What is the difference between an electrolytic cell and a galvanic cell? Explain giving examples. (b) Explain: Mixed potential theory.
[8+8]
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8. Discuss the noble-metal alloying method of improving corrosion resistance of metals. [16]
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Set No. 4
Code No: RR410806
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IV B.Tech I Semester Supplimentary Examinations, May/Jun 2009 CORROSION ENGINEERING (Chemical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain the effect of agitation and concentration of the solution on corrosion rate.
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(b) The corrosion potential of iron immersed in deaerated acidic solution of pH = 3 is - 0.44 V as measured at 25o C with respect to standard Hydrogen electrode. Calculate the corrosion rate of Iron in mdd. Assume that the Tafel slope of the cathodic polarization curve equals to 0.1 V and the Hydrogen ion exchange current density equals to 1 mA/m2 . Atomic weight of Iron = 0.0558 kg/mol. [6+10]
Impurities temperature velocity and Hydrogen concentration.
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i. ii. iii. iv.
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2. (a) How the following affect the amode E-I curve of an active-passive metal?
(b) Explain the construction and working principle of silver-silver chloride reference electrode. [8+8] 3. (a) Indicate the special name for the atmospheric corrosion of the following metal/alloy. Iron and iron base alloy Copper and Copper base alloy Nickel and Nickel base alloy Silver and Silver base alloy
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i. ii. iii. iv.
(b) Furnish isocorrosion charts for Dur iron in sulphuric and nitric acids.
[8+8]
4. (a) How cavitation corrosion is caused? Schematically represent steps involved in cavitation corrosion.
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(b) Describe any four methods to combat cavitation corrosion.
[8+8]
5. (a) Describe the effect of temperature on corrosion. (b) Explain about temperature control and testing method for heating tubes. (c) What are the factors to be considered while writing rate expression. [4+8+4]
6. (a) What are protective currents. What are the factors that influence the levels of protective currents? (b) What is copper-copper sulphate reference electrode? Discuss the potential measurement of a pipe line with the above reference electrode. [8+8] 1 of 2
Set No. 4
Code No: RR410806
7. (a) What is the difference between an electrolytic cell and a galvanic cell? Explain giving examples. (b) Explain: Mixed potential theory.
[8+8]
8. (a) Discuss the effect of velocity on the electrochemical behaviour and corrosion rate of a normal metal corroding with a diffusion controlled cathodic process. [12+4]
