CRV can be understood by using a simple example of milk kept for boiling in a pot on a stove.
The motive, i.e. the reliability of this process has two main factors -
1) The milk should boil.
2) It should remain the vessel and not overflow.
There are three critical variables here -
- Temperature
Why is this a critical variable?
Answer:
The melting point of milk is 92 degrees C. That is the optimum level.
If temperature is too low (30 degrees C), the milk may not boil at all.
If the temperature is too high (200 degrees C), it may burn quickly.
- Vessel dimension = volume of milk is 1 ltr
Why is this a critical variable?
Answer:
Vessel volume < 1 ltr, milk will not fit in it in the first at all.
Vessel volume = 1 ltr, milk will fit, but will overflow on boiling
Vessel volume >1 ltr, milk will fit and not overflow.
- Time
Why is this variable critical?
If the other two variable are at the optimum level, then -
Too less time (~ 1 min), insufficient for milk to reach boiling point
Too much time (~ 2 hours), milk will boil and condense, taste will change
Optimum time (~ 10 min), milk will boil, not overflow, and the heating will be stopped at the correct time.
Thus, maintaining the three CRVs will help to initiate and complete the process of boiling milk perfectly.
So, whenever one has to decide the CRV for larger processes, the important questions to ask are -
- WHY IS THIS VARIABLE CRITICAL?
- WHAT WILL HAPPEN IF IT DEVIATES?
- HOW BAD WILL THE DAMAGE BE?
WATCH THE VIDEO HERE
Reference: "Development of Corrosion Control Document Database System in Crude Distillation Unit", Junghwan Kim, Wonsub Lim, Younghee Lee, Seungnam Kim, Sang-Rok Park, Sun-Kyu Suh, and Il Moon, Industrial & Engineering Chemistry Research 2011 50 (13), 8272-8277
DOI: 10.1021/ie101871a
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