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Wednesday, 18 November 2015

CORROSION FAILURE EXAMPLES

As we have discussed in our previous post about the “Corrosion Engineering” where we have seen the basic of corrosion mechanism. 

Now we will go ahead with this post and we will discuss the engineering materials that may suffer from corrosion. We will see two example of corrosion failure here i.e. Boiler failure due to corrosion and Heat exchanger failure due to corrosion. 

So let us see how an engineering component will be damaged in a corrosive environment

Failure of engineering component due to corrosion

Corrosion is basically a result of electrochemically reactions that will damage the quality of material i.e. it will deteriorate the mechanical and other properties of material and after little time material will not be able to use anymore and if not replaced, material failure will be occurred and therefore the mechanical component will be in trouble.

When we analyze the reason of failure of mechanical component, we will surely consider the case of failure due to corrosion and when we will analyze the failure of component due to corrosion, we must have to secure the following points in order to secure the basic root cause of failure and to secure the preventive action, so let us consider those points that we have to consider during analysis of corrosion failure.
  1. Corrosion types 
  2. Rate of corrosion
  3. The extent of corrosion 
  4. Relation between corrosion and other failure mechanism

Boiler failure due to corrosion

First we need to understand the use of boiler in industrial life, so for what boilers are used in industrial areas?

Boilers are normally used for heating the water for various process requirements in industries. Boilers have significant importance in power generation industries as power unit uses steam for generating the power with the help of steam turbine and other resources and that steam will be produced only by the application of boilers. So I hope you will have brief knowledge about boiler application in industries.
Figure: Boiler tube corroded
Various components of boilers are normally made by cast iron, mild steel, stainless steel and also with high temperature alloys.

Let us consider few common reasons of failure of boiler
  1. Pitting 
  2. Corrosion
  3. Hydrogen damage 
  4. Thermal fatigue 
  5. Stress corrosion cracking 
  6. Caustic gouging 
  7. Acid dew point corrosion 
  8. Maintenance failure
  9. Fatigue failure 
  10. Welding flaws 
  11. Vibration 
  12. Design defect 
  13. Improper operation 
  14. Improper maintenance 
  15. Corrosion of boiler tubes
Out of above reason of failure of boiler component, corrosion and other reason associated with corrosion effect are the key reason of failure of boiler component. Corrosion effect increases if scaling of foreign material increases inside various components of boiler such as boiler tubes etc.

Heat exchanger failure due to corrosion

Similarly, we first understand why we need heat exchanger in industries , heat exchangers are normally used for transferring heat from one media to other media for example for heating the process gases with the help of hot steam is only possible by using heat exchangers.

Figure: Heat exchanger tube corroded
Before selecting the material for heat exchanger, we need to consider few factors and these factors are mentioned below. 
  1. Corrosion resistant 
  2. Heat conduction
  3. Low price 
  4. Strength
Corrosion resistant property is very difficult to secure in a material but we can reduce the effect of corrosion by applying corrosion prevention techniques that we will also discuss later in this literature review report.
Let us consider the common reason of failure of engineering component heat exchanger. 
  1. Corrosion fatigue
  2. Crevice corrosion 
  3. General corrosion 
  4. Stress corrosion cracking 
  5. Erosion corrosion
  6. Improper material
  7. Improper design 
  8. Improper maintenance 
  9. Improper operation 
  10. Pitting 
  11. Tube and pipe imperfections 
  12. Fabrication 
  13. Welding 
We have discussed above two units of power units i.e. heat exchanger and boilers and we have analyzed that environment is quite responsible for corrosion, hence we need to provide corrosive free environment and we will discuss the process to avoid the corrosion also in this literature review report. We should also be aware with the principles used for measurement of corrosion rate

In our next post, we will discuss how we will measure the corrosion