Section A$.$ Instantaneous Corrosion Rate

$26$ Marks

Your development team has been working on a new alloy, Chronious$-89($abbreviated C$89),$ for in the water purification system of your power plant. The pipe will be connected to various alloys used in the water purification system of your power plant. In particular, this material is part of the ion exchange $($IX$)$ resin regeneration system which uses strong acid to condition the resins. The design temperature is $80C$ concentrated water for emergency flushing of the column. Both immersion $($question B$)$ and electrochemical experiments have been performed to test the C$89$ alloy in simulated plant conditions and acid solution $($the IX column regeneration medium$).$ The acid solution is an overtest condition and contains the lowest pH expected in the event of a ${10}^{-6}$ probability failure.

The new material performs very well in $5mo\frac{l}{L}$ sulphuric acid $(H_{2}S{O}_4)$ and the accelerated tests give the characteristics shown in Table A$1.$ The relevant characteristics for nickel are also given in Table A$1.$

A$1.$ Assuming that the mixed potential model can be applied to this system, draw an Evans diagram for the $Ni-C89$ system in $5mo\frac{l}{L}{H}_{2}S{O}_4($graph paper is at the end of this exam booklet$).$ Show your work $-$ no work, wrong diagram, no marks.

$14$ marks

A$2.$ Briefly describe the corroding system based on your analysis of the Evans diagram.

A$3.$ What is the corrosion rate $($as a current$)?$

$3$ marks

$2$ marks

A$4.$ Show how to obtain a useful engineering corrosion rate for this material and clearly state the corrosion rate in $\frac{m}{a}.$

$5$ marks

A$5.$ What is the minimum thickness of the component in order for it to last $52$ months? Remember to state which material will fail.

$2$ marks

Table Al: Electrochemical Corrosion Parameters for nickel and Chronius$-89$

$\backslash$table$[[,C89,Ni,],[$Parameter$,$anodic,units$],[E_{\text{c}\text{o}\text{r}\text{r}},-0\mathrm{.}350,-0\mathrm{.}028,V$