Piperack Design

A.
This sounds like a small plant with rather small lines (largest line is 16") and 1400 lines is not a lot of lines.

B.
So you have a total of 5 small units connected by an interconnected pipe rack, is that correct? The 9 meter pipe rack you are concerned about is the interconnecting rack not one of the unit racks?

C.
Now, having the information about the number of units and the line sizes I do not think you need any 9 meter racks at all.

D.
I do not understand why there are multiple services. This makes no sense to me at all.
To help on this I would need to be there and see the P&IDs and be able to ask a lot of questions.

My Piping Philosophy
1. There is a Rule for everything.
2. There will always be an exception to the Rule.
3. The Boss is still the Boss.
4. Remember Rule #1


Q1. Can anybody advice guidelines for preferred elevation changes when we think of the whole interconnected pipe racks in the entire plant site.
A1. The simple guideline for this is not complicated. Find the largest line size (not counting the Flare Line). The largest line may be the main cooling water supply and return headers, or the primary feed line or the main steam header. These lines feed multiple units and therefore will have branches to multiple units. These lines will be on the main pipe rack levels. The steam header will also have expansion loops which must rise up and cross over the main level.
The elevation changes (vertical distance between crossing levels) should be 3 times the nominal diameter of the largest line. That means that if your largest line is 12" then the crossing level should be 3' -0" above the primary main level. So if we start at grade with a HPFP (High Point of Finished Paving) as Elevation 100'-0" the lowest first deck would be EL 115'-0" (with crossing levels at EL 112'-0" and EL 118'-0"). The second deck of the pipe rack (if required) would be EL 121'-0". The next higher crossing level would be 124'-0" etc.

The Flare line (if applicable) is an exception the rule. It is (or should be) supported separately on one of the extended columns so it can be sloped from origin to the main Knock-Out (KO) Drum or to intermediate KO Drums.

Q2. As per me there should not be any FLAT turns (90 Deg) at all while dealing with off site overhead pipe rack interconnections.
A2. The answer to this is sometimes "Yes" and sometimes "No". Here again there is the "Rule" (no flat turns) and the "Exception" to the rule (flat turn).
I would only use Flat turns in Offsite Tank Farm Sleeper pipe racks where there is little chance for future additions that the flat turn would complicate.

Q3. Can anybody share knowledge about this requirement & how it is achieved?
A3. I hope my additions above help and I also hope that others can offer you their advice and experiences.

Q4. These elevation changes may call for pockets in the line & logically we should avoid it.
A4. You are correct but the key here is "Logically". Logically we cannot avoid ALL pockets in Pipe Rack design unless we are talking about the Flare Header.

Q5. I am very much interested in how we can achieve it that way?
A5. By following the "Rules" of piping it is done time and time again.