Carrier pipe vs casing design? 1

[Orefunto]

Hello again members,
I have another question if you don't mind
I've in the past designed carrier pipes for road crossings using API 1102 but not designed the sleeve or the casing itself.

I'm wondering how the casing/sleeve is different from the carrier pipe?

Your answers would be very much appreciated!

 

[BigInch]

A casing is usually vented and will never contain pressure. It contains a carrier pipe. Carrier pipes carry the gas inside. Not sure what you mean by a sleeve. That might be another name for the carrier pipe???

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Orefunto]

Thanks BigInch,

You're correct and its clear, especially as I talked to a mentor.
The design for the casing (sleeve) is similar to the carrier piper except that the casing (sleeve) will carry the external loads only (dead and live loads )and not the internal pressure.

Pls if you don't mind answering another question:

When I isolate or divide a pipe into 2 sections with anchor and when calculating the resulting force on the anchor, and after obtaining my obtain my force due to friction, e.t.c,do I add or subtract the forces on either side of the anchor in order to obtain the resulting force?

----side 1 force F1--[Anchor]--F2(side 2 force)----

Is it F1 + F2 or F1 - F2?

Your insight would be very much appreciated

Also I calculated my forces as
1. Friction - weight of pipea and content* coef of friction
2. thermal expansion force - pipe Area*(E)*strain
3. internal pressure force - pipe Area * Sh * (.5-v)


Sincerely

 

[Orefunto]

I did a little more research. The forces will be opposing each other, so apparently, I have to subtract. If the lengths are symmetrical, they cancel out and ideally become zero.

I'm not yet satisfied with the pressure force formulae and will research it some more

 

[BigInch]

pipe area is cross-sectional area of the pipe material.

eq #3 is net longitudinal force due to internal pressure.
It assumes pressure on end caps creates an axial tension force in the pipe wall, that when divided by cross-sectional area of pipe material, is the same as the numerical value of the hoop stress / 2.
Sh * [ν] is the longitudinal component of hoop stress due to the Poisson effect. If the pipe's ends are not restrained, the pipe would simply shorten without any effect on stress, similar to a pipe becoming colder and shrinking in length, which does not create any longitudinal force, if the pipe is free to contract. If the pipe ends were restrained, the pipe could not contract and a tension load would be created. In this case, a restrained cold contracting pipe and the restrained longitudinal component of hoop stress, two tension loads, would add, Sh*(0.5 + [ν]) and the net axial force is still tension. 0.8 Sh, when [ν] is typically 0.3
C<- . ->T
-1 0 +1
+----------+-------o--o-----------
combined max shear stress is 0.1 Sh

In a case where a restrained pipe is being heated, a compressive axial load is created. Pressure hoop stress through the Poisson effect would again create a tension load. If compression is considered as a positive sign and tension negative, then they add together algebraically as Sh*(0.5 - [&nu;]) and the net axial force is compressive. 0.2 Sh, when [&nu;] is typically 0.3

-1 0 +1
+-------o--+----------o-----------
C<-.->T
combined max shear stress is 0.65 Sh

Let's check that, because I'm working fast and I have to run out of the house right now.


Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Orefunto]

Again thanks BigInch.

>>If the pipe's ends are not restrained, the pipe would simply shorten without any effect on stress, similar to a pipe becoming colder and shrinking in length, which does not create any longitudinal force, if the pipe is free to contract.<<

What if the pipe is fixed at one end and free to move at the other end?
Would there be forces imposed on the end that is restrained?

Sincerely

 

[BigInch]

No, all it takes is one free end and expansion or contraction is not restrained and no internal stresses are developed.

Note that a pipe fixed on one end, or anywhere, and supported by one or more pipe supports in other places could develop stresses corresponding to the friction factors at the supports. Restraint forces less than or equal to the maximum static friction forces could be developed in the pipe. If the maximum static friction force is reached then the pipe slides and the friction forces would reduce to those corresponding to the sliding friction factor forces.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[Orefunto]

1. So the pressure force would be Sh*(0.5 +/- ?) depending on if the pipe is expanding or contracting?


2 I hope you don't mind that like Oliver Twist, I keep asking for me. I'll try and do a better job of clarifying. If a pipeline segment is anchored at two ends, stresses would develop. If the pipeline is unrestrained at both ends, there would be no stresses at the anchors, since there are no anchors,

But what if I have a pipeline anchored at one end but unrestrained at the other end,

1. would the end that is anchored be subject to forces/stresses?

<Anchor forces or zero??>------------------------->free end


2. If both ends are anchored the force due to say thermal expansion is calculated as A*E*strain. Would this force be fully on each anchor or would it be half of this force on each anchor? Similarly, if I have one end resr


<Anchor F1?>--------Force=say 1000KN------------<Anchor F2?>


Thank you....

 

[Orefunto]

Opps, sorry, I didn't realize you already posted I.see you answered the first part of the question already and that there would be no forces at the one restraint. Thanks, very much.

But on the second part of my last post; would the forces be half at each anchor or the full forces at each anchor?

Sincerely

 

[blacksmith37]

Anther consideration is corrosion ; casing is often a problem. It shields the carrier from cat prot. An alternative is to try to fill the annulus with a non-corrosive solution , and seal it .

 

[Orefunto]

2. If both ends are anchored the force due to say thermal expansion is calculated as A*E*strain. Would this force be fully on each anchor or would it be half of this force on each anchor?


<Anchor F1?>--------Force=say 1000KN------------<Anchor F2?>


Looking at this , I'm thinking the forces should be split over the two end anchors

 

[BigInch]

If both ends are anchored, full force.
If one end is anchored, no force. Must have at least two anchors to be restrained.
Unrestrained = unrestricted expansionm hence, no expn force.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus