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[Nirav]

hello,

my question is related to chemical as well as piping engineering.
In one of the projects I'm working on, I have been asked to provide a fluid category for each pipe class mentioned on PMS (Piping Material Specifications).
The category to be identified is with respect to ASME B 31.3. i.e. Type 'D', Type 'M', 'Normal' or 'Severe Cyclic'.
I am able to understand on "how to" identify such category EXCEPT for "severe cyclic" condition.. I am trying to understand the concept of "severe cyclic condition".

I refered ASME B31.3 (section 300.2 - Definitions). As per its explanations, we need to identify total no. of "cyclic conditions" over the entire life span of the plant. By definition, it is "equivalent number of full displacement cycles during the expected servide life of the piping system."

So, what is the meaning of this definition ??? How do I decide such cycles?
As per ASME B31.3 if total no. of such cycles exceeds 7000 in entire life, it can be considered as "severe cyclic condition". For example, 1 such cycle per day for 20 Yrs. pant life would exceed 7000 (1 x 365 x 20 = 7300 > 7000).

During discussions, I came to know about one example of cyclic condition. i.e. A moisture removing 'mole.sieve' bed. This kind of system will go under "operation - regeneration - operation" cycle which has very vast difference in operating temperature. In a typical drier, this cycle may repeat once or twice in a day.
So, pipe lines under such exposure would have fatigue life and thus needs special attentions from stress analysis and NDT checks etc. This needs to be identified as "severe cyclic condition" on PMS pipe class.

Now, for each and every pipe class, how can I identify such cyclic operation ???

What kind of variation in temperature can be considered as "cyclic" ? I do not think normal up & down in temperature or pressure for process control can be considered as 'cyclic'.

Is there any other criteria for considering the operation as "cyclic" in nature from operations point of view? e.g. pressure surges, temperature surges etc....!!!???!!!

I am doing this exercise for the first time. Therefore, lots of questions are arising in my mind. Probably, an experienced person would be able to help me out.