Thanks a lot Jop.

Just little more clarification pls.

As for spec you mentioned it should be indicated on downstream of valve.

My concern is: Why we are bringing valve at higher rated side.
And suppose if we have spec breaks that are of same rating each side, Why yet we indicate it downstream of valve.

Regards

Why we are bringing valve at higher rated side?
The valve must be the higher rated line class because when it is closed it must "Hold" the higher pressure of the higher line class.

And suppose if we have spec breaks that are of same rating each side, Why yet we indicate it downstream of valve?
If the piping is the same rating on both sides of the valve then you should have the same line class on both sides of the valve and you don't need a "Spec Break".

And suppose if we have spec breaks that are of same rating each side, Why yet we indicate it downstream of valve?
If the piping is the same rating on both sides of the valve then you should have the same line class on both sides of the valve and you don't need a "Spec Break".

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Same rating can still have a spec break - possible if there is a change in pipe material.
For example, one side of the piping run is CS-300#. And on the same line I can have another material say SS-300# welded to it due to some process change. Process change came about due to injection. Happen all the time in a complex process plant.

There are two reasons for a "Spec Break" in piping.
The first reason for a Spec Break is a change in Pressure and therefore flange rating (higher rating down to a lower rating)
The second reason for a Spec Break is a change in Material (example: Stainless Steel to Carbon Steel)

Therefore you DO need a "Spec Break" even though there is no change in the basic flange class rating.