Q1
In a modern business environment successful organizations cannot tolerate major corrosion failures especially those involving people, processes, and procedural and management, the specific needs for corrosion education vary greatly with the level of education required the function expected of the personal and most importantly the application where corrosion is a concern. The European federation of corrosion (EFC) has identified four categories of corrosion personal based upon their particular activities such as follow:
- Group A corrosion scientists and engineers
- Group B technologists
- Group C technicians
- Group D operatives
a)Based on the results of engineers activities why is corrosion study important in perspective of
- Process safety and loss prevention?
- Managements?
Elaborate your points accordingly
b)Distinguish between the 2 types of corrosion chemical and electrochemical corrosion.
Solution:
Q2
a)Compare and discuss briefly on the differences between the galvanic and electrolytic cells. Illustrate both cells in detail. Tabulate your comparison.
b)Figure 1 represents a silver electrode is immersed in silver nitrate (AgNO3) and a copper electrode is immersed in a copper nitrate Cu (NO3)2 to form a galvanic cell at the standard condition.
Free Gibbs energy of electrochemical reaction = -n.E.F
Where, n= number of electrons exchanged
F= Faradays constant= 96500 coulomb per mole of electrons
Ecell = the potential difference between the cathode and anode in the cell
- Determine the half-cell reactions involved and the overall cell potential
Answer
- Evaluate the direction of reaction if spontaneity occurs
- Which metal is corroding?
- What would be the maximum energy available?
Given, standard half-cell potential for copper e0 = 0.337V
Standard half-cell potential for silver e0=0.799V
Solution:
Part B
Underground pipeline system to supply water is generally made of ductile iron.
Ductile iron pipe is a pipe made of ductile cast iron commonly used for potable water transmission and distribution. This type of pipes is a direct development of earlier cast iron pipe, which it has suspected. The ductile iron used to manufacture the pipe is characterized by the spheroidal or nodular nature of the graphite within the iron. Typically, the pipe is manufactured using centrifugal casting in metal or resin lined moulds. Perspective internal lining and external coating are often applied to ductile iron pipes to inhabit corrosion. The standard internal lining is cement mortar and standard external coating includes bonded zinc, asphalt or water-based paint. In highly corrosive environments loose polyethylene sleeving (LPS) to encase the pipe may also be used. Life expectancy of unprotected ductile iron pipes depends on the corrosiveness of soil present and tends to be shorter where soil is highly corrosive.
The major corrosion concern in the water works industry is galvanic corrosion. Galvanic corrosion takes place due to current flow in a galvanic cell which is defined as
- Two dissimilar metals, an anode and cathode,
- In electrical contact with each other and
- Common electrolyte
A galvanic cell is produced when the pipeline components come in contact with the soil. In such a cell, one of the metals, the anode, corrodes away and other metal, the cathode, is protected. The rate of the corrosion is dependent on the current and the current density, which are functions of galvanic potential difference.
Several factors of the soil conditions and environment affect the corrosively of the pipes namely pH, resistivity, moisture, oxygen concentration and chloride and sulphide content of the soil. The measurement of soil resistivity in UPM surrounding area was found to be between 32 and 1685 Om depending on the site. Higher value was found where the site has low water table.
You are required to design a water piping system for UPM with information above. Propose a corrosion protection method and test needed to evaluate and monitor the corrosion rate at selected sites. Elaborate the methods proposed and justify.
Solution: