Expansion Loop Spacing 5

[LuckyCharms]

I'm a young engineer in an environment lacking of pipe stress experience. To this point I've been responsible for pipe stress analysis of O&G facilities. I've picked up all I currently know from these forums, textbooks recommended on here, and through pipe stress programs. I've gotten by fine until recently, much to the indirect help of all of you. Thank You.

To my question - I've been tasked with analyzing a 10 mile straight segment of 36" above grade pipe for crude transportation. All in all, with thermal expansion and pressure elongation, I've found that there could be upwards of 40' of expansion over this length of pipe. Given this scenario, I've done research into expansion loops and found many resources for sizing and guide placement but I haven't found much for spacing. Ignoring space limitations, what is the difference between anchoring the system every 500 feet with an appropriately sized, centralized loop and anchoring at both ends of the 10 mile stretch with an appropriately, all be it large, centralized loop?

I've run both scenarios in AutoPIPE and found that stresses are not an issue, but the axial anchor loads resulting from the use of a single large loop are an entire decimal place larger than that seen with a multiple loops system. In both systems I used shoe supports spaced 40' apart with friction considered.

I'm sure this is simple, but I've learned that length of pipe has no bearing on ideal axial anchor loads, only temperature and material properties play into this number. If loops are sized to take the full expansion over their respective spans, I would have expected to see similar loads in both systems. Is this due to the friction from the supports?

Thanks in advance.

 

[pennpiper]

GrassyNol,
Some additional information is required;
What it the maximum expected operating temperature?
Where is this pipeline located?

I would look at possible physical needs first;
#1 Will this pipeline be located low to the ground on Sleepers Supports? or will it be elevated on a Pipe Rack which will allow traffic underneath?
Will there be any road crossings in this 10 mile stretch? Road crossings can be incorporated in your Loop plan if your pipeline is designed to be supported on low sleepers.
#2 Loops will NOT work if you do not have anchors (and Guides) on each side of each Loop.
#3 Each Loop should not be required to handle more than 6" of expansion. What is your total (worst case) expansion?
#4 Loops can be horizontal or vertical. Horizontal Loops can be single plane or double plane. Vertical Loops can travel on Sleepers (low to the ground) then rise up and be supported over a road crossing then drop back down and continue on the Sleeper level.

There are lots of options.




Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

The more loops you have the smaller they can be. High temperature lines can need expansion loops every 100ft.
Take it from there.

 

[LuckyCharms]

pennpiper,

Thanks for the response.

There's a maximum operating temperature of 130 deg F and it will be low to the ground with horizontal single plane loops. The maximum expansion looks to be roughly 40' given maximum temperature and pressure.

There's many ways of handling this, but I'm more so interested in the dynamics of expansion loops. I've found lengthy literature on sizing the loops, but I haven't seem much in terms of how the anchors are affected on a single loop designed to mitigate 5 inches of expansion versus a loop designed to mitigate 50 inches of expansion. In turn, I'm very curious about the 6" of expansion, as that would simplify my process. Is there a standard for this or is it common industry practice?

Thanks,

 

[BigInch]

6" is a lot higher than what I would be comfortable with. I'd think that a 25-30 ft dogleg would be a reasonable loop size for 36" pipe. The longer the dogleg, the lower the stress. The lower the stress, the lower the anchor force.

 

[pennpiper]

Grassy,
I have more questions for you.
Is there an easement? How wide is your easement. Will there be a fence? The reason I am asking this is, if your easement is only 100' wide then your pipeline, the loops and a maintenance access roads (possibly one on each side of the pipeline) would need to be contained inside the 100' strip. This would have an limiting affect on how long the legs (of the loop) can be.

Sometimes its possible to do all the right things and still get bad results

 

[LuckyCharms]

Thanks BigInch.

pennpiper,

You're right, there are important constraints that I'm not currently considering. I should have prefaced this by stating that at the moment this is only a feasibility study and there are many other variables that would have to be accounted for if this project were to move forward. As an inexperienced engineer with resources at hand, I've designed two systems that both satisfy the loop length equation of L=√3EDΔ/S (One with multiple anchored loops sized for 5" of expansion over 10 miles and one with a large single loop sized for 40' of expansion within the 10 miles).

My question was why was I seeing such dramatic differences in anchor loads for either hypothetical system? Especially since each system is realizing similar pipe stresses and accounting for similar percentages of the expansion over that length (per AutoPIPE). So what's the cause of the high anchor loads in the system built for 40' of expansion as opposed to that built for 5" of expansion. I imagine this could be something as simple as the bending moment at the loop being that much higher with the larger loop, but I had some doubts as to what factors come into play.

 

[BigInch]

High anchor loads are due to short doglegs, high temperatures and thick pipe walls. Axial stress caused by thermal expansion is uniform through the wall, hence pipes at the same stress, but different walls, will yield correspondingly different anchor loads. Short doglegs make anchor loads nearly equal to axial stress x pipe wall area. Longer doglegs will tend to disburse axial load into bending moment.

 

[pennpiper]

Grassy,
What are the things that should be considered for a Pipeline project?
Here are a few things to consider (just alphabetical order)
Cathodic Protection requirements Study
End Point Meter Station and Meter Prover
End Point Pig Receiver Station
Expansion/contraction study
Feasibility Study
Geographic Profile Study
Hydraulic Analysis
Intermediate Pump Station(s) analysis (possible additional Pumps Pig Receivers and Pig Launchers)
Installation location & manner (Above or underground, on sleepers at grade or elevated pipe racks or combination)
Local, State, Province and Country Code Applications
Maintenance plan
Materials of construction study
Pigs (Purchase or Contract a Service as required)
Pipeline Instrumentation plan (SCADA)
Pipeline Operation Philosophy Study
Pipeline Security facilities (fencing, motion detectors, armed guards, etc.)
Preliminary Estimate of Construction Costs
Preliminary Material Estimate, Pipe, Pumps, Compressors, Drivers, Valves, etc
Primary (Start Point) Pump Station Layout
Property Searches
Right-a-Way acquisition
Right-a-Way Approval
Right-a-Way Permits
Right-a-way Planning
Right-a-Way width
Road and Highway Crossing Permits
Road and Highway Crossing Study
Routing Studies
Soil Corrosion Analysis
Start/End Point Meter Station and Meter Prover
Start Point Pig Launcher/End point Pig Receiver
Water Way (River & Stream) Crossing Studies
Water Way Crossing Permits
-
And, the ten other items I have not thought of that will jump up and bite you in the pocket book for another 10% of Cost


Sometimes its possible to do all the right things and still get bad results

 

[Gator]

pennpiper, it's almost as if this pipeline stuff is quite complicated and probably deserves competent, knowledgeable and experienced people to execute projects, isn't it?

Sorry.

Piping Design Central

 

[MJCronin]

Bravo, Gator ! ! Looks like the MBAs have struck again !

How many times on these for a have we encountered the hapless yet sincere newbie trying to learn piping engineering on a complex and expensive CAPEX project !

Often, I have wondered about the management wisdom of someone who would place a new engineer in a position where so much expensive damage can be done... Isn't it obvious how things will go ?

We all know who will lose their job and career enthusiasm when things go badly wrong.....

MJCronin
Sr. Process Engineer

 

[KevinNZ]

Pennpiper, Your extra 10 things will include wind, seismic and friction loads. it's an above ground pipeline.