Anna University Corrosion and Surface Engineering Question Paper



IV Semester Metallurgical Engineering


Time : Three hours                                                                        Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1. Distinguish between e.m.f. series and galvanic series. (any four points)

2. What is Pilling–Bedworth ratio? Mention its significance.

3. What is turbine corrosion? Where is it encountered?

4. Define corrosion inhibitor. Name two inhibitors each for acidic and neutral media.

5. Indicate two purposes of corrosion testing.

6. What is intergranular corrosion? Mention an alloy most susceptible for this attack.

7. Define passivity. Name the element responsible for atmospheric corrosion resistance of stainless steel.

8. What is Tafel equation? Mention  its application.

9. What is electroless plating? Give two examples.

10. What is cathodic protection? Mention its two classifications.

PART B — (5 ´ 16 = 80 marks)

11. (i)      Draw Pourtaix diagrams for Fe/H2O, Mg/H2O and Al/H2O systems at room temperature. Mark the regions.                               (10)

             (ii)     Explain auto catalytic nature of pitting corrosion and also its remedial measures.                                      (4 + 2)

12. (a)     (i)      What is dezincification? Explain its cause and remedial measures.
(2 + 4 + 4)

                       (ii)    Indicate the parameters involved in atmospheric corrosion. Graphically explain the influence of relative humidity on atmospheric corrosion of metals.            (2 + 4)


             (b)     (i)      Explain carbondioxide corrosion in boilers. How will you prevent it?
(4 + 2)

                       (ii)    Write a note on :

                                Inspection and analysis of corrosion damage in boilers.         (5 + 5)

13. (a)     (i)      Discuss, in detail, various susceptibility tests for intergranular
corrosion.                                                                                            (12)

                       (ii)    Explain accelerated weathering tests.                                             (4)


             (b)     (i)      Describe salt spray humidity and various porosity tests.       (4 + 6)

                       (ii)    Furnish the details of various classification of corrosion testing methods.                                  (6)

14. (a)     (i)      Briefly describe three different types of electrochemical
polarisation.                                                                                       (12)

                       (ii)    Write a note on : Effect of oxidising agents in passivation of metals.


             (b)     (i)      With a neat sketch, discuss active-passive behaviour of austenitic
stainless steel in sulphuric acid medium.                                      (12)

                       (ii)    Explain various factors governing passivity.                                  (4)

15. (a)     (i)      Distinguish between anodic and cathodic protection. (any five
points)                                                                                                 (10)

                       (ii)    Explain arc spray and flame spray processes with suitable examples.                               (3 + 3)


             (b)     (i)      What is anodising? Mention two metals which are commonly anodised. Indicate the advantages of anodising.         (2 + 2 + 2)

                       (ii)    Discuss, in detail, various classifications of corrosion inhibitors with
examples.                                                                                            (10)


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