Important terms in API certifications – CRV & IOW – III


IOW can be understood by using a simple example of milk kept for boiling in a pot on a stove.

The definition as per API 584 is 
 “established limits for process variables (parameters) that can affect the integrity of the equipment
 if the process operation deviates from the established limits for a predetermined length of time”

What are the important words here? 

  • established limits 
  • process variables 
  • affect the integrity of the equipment
  • process operation deviates
  • predetermined length of time
In the above example, let us keep the time as 1 hour.
Now there are two critical variables here-

      • Temperature 

What is the IOW for temperature?

The melting point of milk is 92 degrees C. That is the optimum level.
For 1 hour, if temperature is below 40 degrees C, it may not boil at all.
If the temperature is  above 120 degrees C, it may condense.
So, the IOW = 40 – 120 degrees C

      • Vessel dimension = volume of milk is 1 ltr

What is the IOW for vessel?

Vessel volume = 1 ltr, milk will spill over.
Vessel volume = 1.5 ltr, milk will boil, and may not overflow.
Vessel volume = 3 ltr, milk will fit and not overflow.
So, the IOW = 1.5 – 3 ltr

Thus, the IOW tells us what the range is for the safest and cost-effective process.


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