Piperack Design

This question should have been posted on the "Technical Forum and it is one that has been asked before.

There is no formula. There is only instruction, training and experience.

Here is the question asked before and my answer:

Pipe Rack Sizing
The question:
“How do you size a pipe rack? What are the steps?”

My answer:
Pipe Rack Height - The height if a pipe rack is based on the minimum overhead clearance required under the lowest level of piping passing transverse under the rack (normally 12'-0" +/- or 4 meters). Then the vertical spacing of the North-South (N-S) and East-West (E-W) levels is determined by the largest average line size in the rack. If your largest average line size is 12" NPS (a 12" long radius Ell is 18") then, two Ells welded together results in 3'-0' center to center of pipe (also 3'-0" bottom of pipe to bottom of pipe). This means that the vertical spacing between the N-S and the E-W rack should be 3'-0". If you only require one level then you will have the original grade (ground) to lowest crossing level which may be 12'-0" plus 3'-0" to the first rack level for a total of 15'-0" For every rack level you add you must double the 3'-0" to allow for another crossing level between the normal rack levels. The final overall height of the rack is determined by the number of levels required and any other special conditions or requirements. Special conditions include mounting Air Cooled Exchangers (Fin Fans) on top of the pipe rack or the requirement to have the flare line slope to free drain to the Flare Knock-out Drum.
Pipe Rack Width - The width of any given pipe rack is best determined early in the project during the Plot Plan development activity by doing a “Piping Study” (See Piping Study included in this paper). You must have well developed P&ID's and an understanding from the structural group on the type of supports construction (i.e.: bare steel, fire proofed steel, pre-fab concrete, or poured in place concrete). You then take the preliminary equipment arrangement (does not need to be to scale) and allow a clear space where you know the pipe rack will be located. Then take every line from the P&ID that you know will need to run on the pipe rack and "sketch" it onto the pipe way area of the preliminary plot plan. As you go make sure you identify every line with the line number, line classification, line size and insulation if required. Do not make it detailed; keep it a very simple "stick" drawing. Do this with all lines. This drawing is also called a "Transposition" and the activity is called doing a "transposition." Once you have completed the transposition and all the lines shown then you can find the most congested point of the pipe rack. Study the most congested point to determine the most appropriate line sequence. By this I mean which lines need to be on the east side of the rack, which lines need to be on the west side of the rack and where the other lines should be? Next you need to calculate the spacing between each two lines individually. To do this you take one half the diameter of the flange of the largest of each two lines + one half the outside diameter of the other pipe + the thickness of any insulation on the smaller line if any + 1" spacing. Do this for all pipes in the congested part of the transposition. Now add the line spacing for a raw total. To the raw total you should add 30% for lines that may be added during Design Development. You should also ask the client how much "Future" rack space is wanted (normally 10%) for the finished plant. The raw total plus the 30% plus the 10% may give you a number that is acceptable for a one level rack. However you may find it is more likely that you will need two or more main levels. Work with the numbers, considering the overall space available, the span of the proposed rack and the loading to be placed on the span.
Line Spacing - Line spacing is (a)one half the diameter of the flange of the largest of each two lines +(b)one half the outside diameter of the other or smaller pipe + (c)the thickness of any insulation on the smaller line if any + (d)1" spacing.

Here is another question that is important to Pipe Rack sizing.

Pipe Spacing
The question:
Hello there....do you have table for standard pipe to pipe spacing.....

My answer:
It is always helpful to know, understand and remember the basis for line spacing. Different engineering companies and owner (client) companies may have their rules but the most common minimum pipe spacing rule is as follows:
- Flange-to-pipe + clearance (+ insulation if any)

This means:
For hot insulated lines with the same flange rating, line spacing includes 1/2 the O. D. of the flange for one line (largest if different sizes) + 1/2 the O. D. of the other pipe + 25mm (1") + the thickness of the insulation on the smaller line (if any)

For cold insulated lines with the same flange rating, line spacing includes 1/2 the O. D. of the flange for one line (largest if different sizes) + 1/2 the O. D. of the other pipe + 25mm (1") + the thickness of the insulation on the flange + the thickness of the insulation on the smaller line

Notes:
1, it is common practice to always stagger flanges when ever possible.
2, it is common practice to insulate the pipe in hot services and leave the flanges bare.
3, It is common practice to insulate both the pipe and the flanges in cold services.

In cases where flanges cannot be staggered then the rule is adjusted as follows:
- Flange-to-flange + 25mm (1") (+ any insulation on the flanges)

For line spacing where one line is a higher flange rating you should take 1/2 the flange diameter of the flange that has the greater flange width or extension. The extension if a flange is equal to the radius of the flange minus the radius of the pipe.

Example:
Line (a) 24" 150#
Line (b) 8" 1500#
Which line would you use for the "1/2 flange dimension" in the calculation for line spacing?

The flange width for line (a) is 4"
The flange width for line (b) is 5.188"

If you use the normal pipe spacing rule then the flange of line (b) will hit the pipe of line (a).

I have created a spreadsheet showing the worst case flange extensions for all of the standard flange sizes and ratings. I will be happy to send it to anyone who would like to have it.
Just E-Mail me >> This email address is being protected from spambots. You need JavaScript enabled to view it. << and ask for the:
"Quick Worst Case Flange Extension Chart"

Point #1. You did not indicate the location of this specific pipe rack. Is it an off-site interconnecting pipe rack or is this a Unit pipe rack? You also did not indicate the type of overall plant (Refinery or Chemical Plant) and you did not give any idea of the size of this overall plant. You did not say if this is a mega-plant or is this just a small add-on unit to an existing plant.

Point #2. You did not give any idea of the line sizes in this pipe rack.

Point #3. You did not say if there is a space limitation or restriction that is forcing you to squeeze things close together.

Point #4. A 9 meter (wide) pipe rack is not unusual for the typical large (or mega-plant) being built today. Even twenty or thirty years age I saw 10 meter pipe racks.

Point #5. If you are in the conceptual stage as you say then I would advise to go with the 9 meters (or round it up to the even 10 meters) and look at cutting back later when necessary.