Discuss, in your own words, THREE conditions where corrosion is initiated
via
(b) A “salt-water drop” experiment was performed on a sheet of clean steel in
the laboratory.
(i) What is the name of the indicator used?
(ii) What did the indicator contain?
(iii) Draw a sketch of the results, explaining what colours could be seen
and what caused them.
(iv) What type of corrosion cell does it demonstrate?
The Pourbaix diagram shows the predominant form in which an element
will exist under a given set of environmental conditions. Pourbaix diagrams
display
(i) For a given metal what equation is used to construct a Pourbaix
diagram?
(ii) Three regions are identified in the Pourbaix diagram, what are these
regions and what information do they provide?
Predict the possibility of galvanic corrosion in sea water for the following
coupled pairs of alloys and metals. Using the Galvanic Series Sheet please
provide a reason for your answer.
(i) Aluminium alloys bolts and 80-20 Copper-nickel, CDA 710 sheet.
(ii) Plain carbon steel pipe and manganese bronze sprinkler.
(iii) Low alloy steel tube and stainless steel 410 sealing ring.
(iv) 4130 Alloy steel subsea crossover and stainless steel 430 API gasket.
(v) Graphite gasket and Inconel 625 flange.
(b) In your own words explain the mode of action of an anodic and a cathodic
inhibitor.
The potential of a zinc electrode on which Zn deposits from a 0.1 M ZnSO4
solution is -1.1 V vs. SCE.
(a) Determine the zinc deposition voltage on the hydrogen scale.
(b) Determine whether zinc oxidation or reduction occurs at this potential.
(c) Pitting corrosion of stainless steel can occur in the presence of a high
chloride concentration.
(i) Describe, with illustrations and relevant equations, TWO types of
pitting corrosion mechanism, providing chemical equations where
necessary.
(ii) In each case discuss how you would prevent them occurring.
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