Expansion Loop design: loop size vs spacing 5

[yukon09]

I am working on expansion loop design for a mining project. after I calculated the thermal expansion of the whole pipeline, I met the problem of sizing and spacing the Eloops.
I have used the method introduced in Design of Piping System by M.W.Kellogg to decide the dimension of the Eloops. And sometimes I use a table in ASHARE handbook to size the Eloops. It is easier.
But I don't know how to determine the spacing of the expansion loops. I understand that the spacing distance is related with the size of the ELoops. The bigger the Eloop is, the longer the spacing would be. But how to compromise the size and the spacing of the Eloops? More important for me, how to determine the spacing of the ELoops if I have to put many ELoops in the pieline?
I am not sure I explain the problem clearly or not but I appreciate any kind of advices or hints greatly!

 

[pennpiper]

Here is a question and my answer from some time ago. I hope it helps.

Piping Loops
The question:
“How do I determine the location for anchors and the size of an expansion loop?”

My answer:
You want to know how to handle layout problems that involve long runs of pipe, thermal expansion, anchors, guides and ways to compensate for expansion.
This is a basic problem for all novice pipers and is one that is not easy to explain. However let me try. First, I think you need to look at the whole system and come to a solution based on that whole configuration.
There are four basic options to compensate for thermal expansion in a piping system. These options are as follows:
1. Do nothing. Just allow enough room on the pipeway and let the pipe expand and contract as it will. It will create its own friction anchors and will “snake” around as required to compensate for the expansion. This is not a highly recommended option.
2. Normal configuration. This is where there are natural changes in direction of pipeways or routing that will compensate for the thermal expansion. Natural configuration is defined as a basic “L” shape or a “Z” shape. Anchors and guides need to be installed to prevent the thermal growth in one line from interfering with another. If all the legs are the right length and the anchors and guides are placed correctly then you will not need additional methods to compensate for the expansion.
3. Expansion loops. In long straight runs of pipeways pipe expansion loops are added to compensate for the thermal expansion. Anchors and guides are required to control the pipe and insure that the loop will work as designed.
4. Expansion joints. Expansion joints of various types are made and used to compensate for expansion in piping systems where there are space limitations or natural configuration or loops are not an option. Systems with expansion joints also require pipe anchors and pipe guides to work properly.

You need to ask yourself:
Where do I have natural turns that can be used to compensate for expansion?
Where do I have branches? And do these branches create potential problems?
Where do I need to add loops?
Where can I place anchors and guides?
What is the distance between the potential anchor points?
Now!
What size loop do I need for the places where natural configuration will not work?

Now, the question is not how much pipe should you have between expansion loops but what size an expansion loop should be for a given distance between anchor points of a line.

The answer to this question is really simpler than would first appear. Let’s say you are doing layout for a “Unit” which branches (west) off the main north/south offsite interconnection pipeway. The line under consideration is a medium pressure steam line with 8” schedule 40 pipes and a temperature of 450 degrees F. There are battery limits block valves at the interconnecting pipeway end and the line dead-ends at the other end of the unit.
Your pipeway (or sleeper way) has a specific spacing and width. We will use 10 pipe supports at a spacing of 25 feet each and a width of 25 feet. Number the supports from right to left as PS #1 through PS # 10. You know you need one or more loops. You also know that the loops need to be supported. You also recognize that you can use option 1 (above) for some of the header. So, start out by placing your first anchor two pipe supports in from the dead-end of the unit at PS # 8. You will let the last 55 feet (+/-) of header to “free expand.” Next move to the battery limits end of the pipeway and place an anchor at PS #1 nearest to the battery limits block valve.
Now look at the distance between the two anchors. Is this distance less than 200 feet? If it is less then you should need only one loop. This loop should be as near to the halfway point between the two anchors as practical. Our distance between PS #1 and PS # 8 is 175 feet. The halfway point is between PS # 4 and PS # 5.
The line will run in the first pipeway berth at the far south side of the unit pipeway. The loop will rest on a support beam on the north side of the unit pipeway and cantilever out about 5 to 6 feet. This makes the loop with dimensions as follows: a vertical rise up 2’ – 6”, a leg north of 23 feet, a flat turn and a leg west of 20’ – 0”, then a flat turn south of 23 feet and a vertical drop of 2’ – 6” back into the lines assigned berth.
You have already placed an anchor at PS # 1 and at PS # 8 so the next thing is to place guides. The guides need to be one pipe support away from the loop. So the guides are placed at PS # 3 and PS # 6.

This is what I mean by being simpler than would first appear. 90% of the time you can use the “natural landscape” to help to do the loop design instead if worrying about a lot of calculations.

Please note: this being a steam system it will still need to have a proper check and/or analysis by a qualified Pipe Stress Engineer.

 

[yukon09]

Thank you so much for your great help on our new pipers.
I still need some time to digest your points and get the idea about the ELoops.

 

[LSThill]

Also: do advance search: Expansion Loop

http://www.eng-tips.com/viewthread.cfm?qid=235691

 

[rneill]

If you do a search here or with google, you will likely turn up a variety of Rule of Thumb type guidance documents for loop dimensions and spacing for given temperature changes and/or material expansion. Myself, I used to have a slide rule for quick sizing (but unfortunately I lost it a few years ago).

However, these tools are best for preliminary layout and I would never want to base a final design on a rule of thumb tool of unknown origin so it is best to have final confirmation from a qualified stress engineer using a tool such as Ceasar II.

 

[LSThill]

Ceasar II Verson 5.20 now has Expansion Loop design: loop size vs spacing

 

[yukon09]

Thanks for all of you.

 

[sanjay300864]

Place the expansion loops and anchors in such a way that axial movement of pipe on supports does not exceed by 100mm.

 

[TGS4]

sanjoy300864 - care to justify that 100mm requirement? I've designed expansion loops such that the axial movement of the pipe was 12in - just needed to add long support shoes for thermal expansion greater than 4in.

 

[rneill]

Agree with tgs4, in systems with high temperatures, it would be impractical to achieve maximum movement of 4". Myself, I've designed for 12" before with high pressure steam lines. As long as the stress calc's meet, the shoes are long enough (I usually make them double the expected movement), and there is enough room on the rack to allow the calculated movement, there should be no problem.

Note: people often forget to consider multiple cases when designing the spacing of piping on racks through expansion joints. For example, you might consider all pipes cold or all pipes hot but you have to also consider the case where one line might be hot but the adjacent lines cold (e.g., out of service).

 

[sanjay300864]

Piping Elders,
Agreed, there is no justification for 100 mm requirement.
Maximum movement of 100mm is a conservative number. If one restricts axial movement to 100mm, no additional precaution is required.
I had also come across higher values with longer shoes or off center shoes. But these requires extra precaution during installation, which irritaes our friends of construction.