Pipe Stress Analysis

[alwaw911]

THanks a LOT Freeman for such nice and profitable topic...guess reviewing the basics should be the next thing to do (for me)!!!

Best regards and keep posting or sharing ur knowledge.+1

[A.Venugopal]

Dear MTD,

I chanced upon your query which was posted quite long ago, much earlier to my joining this great forum. I do not know whether you did get replies or you still need answers , If you are still looking for answers , then I shall try.

I also invite other friends to post their questions on pipe stress analysis here so that it helps all.

Best regards

Venugopal

[FATHI]

How to dsign and pre-size pipe rack ..???
Do you have specifications or guidelines ??

Which margin is taken for future lines as a general rule ??

Sizing occurs before pipe stress= How can one take into account the axial and lateral loads generated by anchors,Stops, guides ???

Thanks you all !!!!

[unni]

Very Very Intersting one freeman

[maskedsperm]

Freeman,
Thanks a lot for ur valuable explainations its great
really its a worth for any piping engg.
Based on ur explainations i would like to some more questions
1) How the piping loads on pipe rack are given (with Units) before doing any stress analysis (preliminary loading). What is UDL Concept and point load concept?
Any book, notes, guide lines?
2) How Anchor loads on piperack are calculated before stress analysis on pipes?
3) How to decide anchor bay ?
4) In hydrotest the pressure is taken as 1.5 x design pressure but asme 31.3 allows max. of 1.33 % design pressure than how pipe line sustain 1.5 x design pressure it suggests that after hydrotest pipe becomes useless
5) In thermal expansion or contraction how the perpendicular leg is calculated?
is there any formula for that? because refering charts for each dia and each material is difficult. Any book?, notes?, guide lines?
6) Do u have same expertise on piping materials? so that I would like to ask some more?

Thanks
MTD

MTD...

I'll try to answer your questions... But, be aware some of the figures shown in my answer might vary from Project to Project. Please, check Current Project Piping Stress Specification for real/applicable figures to be used by you...

1) Before Piping Stress Analysis, Piping submites only weight loads to structural guys. You calculate the weight (metal + water, since Hydrostatic Test Weight is the worst case scenario) of a pipe section whose length is equal to the span between pipe rack supports and divide this figure by 2 (since that weight will be supported by 2 supports). That's the Vertical Load. Axial Load will be the result of multiplying Vertical Load by the Friction Coefficient. With these Loads, stuctural guys size (preliminary) the structural members of the rack until you finish pipe stress analysis and get actual Loads from the used software reports.

2) Piping Stress Engineers and Piping Design guys work together to achieve resulting axial loads on Pipe Anchor supports to be less than a certain figure (let's say 2,500 pounds... it will depend on the anchor design itself) by providing flexibility to piperun (using loops or re-routing the pipeline). Please, understand that on a pipe anchor supports there will be axial forces acting against each other (one from the pipe section upstream the anchor, the other from the section downstream the anchor) so if you end up with simetrical pipe runs at each side of the anchor support you'll have a resulting axial force on the anchor tending to be equal to cero (ideally).

3) Having a very long (straight) pipe on a very long pipe rack, the first thing to do is to calculate the thermal expansion of the given pipe run. If the calculated expansion is greater than 12 inches, the first approach is to include one anchor at the mid point (as close as possible) of the pipe run and add two pipe loops (one at each side of the anchor). This will be the location of the anchor bay. If the resulting expension -for each half of pipe run- is still greater than 12 inches, then you divide the pipe run in three sections in order to add three pipe loops and two anchor points (and anchor bays). And the iteration process goes on and on untill you reach the desired expansion figure for each section of the pipe run.

4) Don't know where this 1,33% (at ASME B31.3) is coming from... I'm not aware of that. But If by using 1,5 x Design Pressure as Test Pressure you're exceding 0,7Ultimate Strength of the selected material, what you need to do is upgrade your material selection to a steel with higher strength. Revise the Piping Class of this pipe run.

5) When using "manual" methods for studying piping flexibility, such as guided cantiliever (I think this is where your question is referring to), "perpendicular legs" are the lengths of all the piping sections perpendicular to the one whose reactions you're studying in particular. So you add all lengths of these perpendicular pipe sections, input the resulting value into the corresponding formula (or chart) then you get the estimated reactions you're looking for. Please, refer to Kellog's "Design of Piping Systems" (is available in this forum)

6) Some expertise.... maybe lees than what you need to get the answers you're looking for... I'm not a Piping Stress Analysit nor a Material Engineer either... I'm an experienced Piping Designer/Engineer, so... wait for Freeman's answer...

Best Regards

I hope I helped (at least) a little.....

[maskedsperm]

How to dsign and pre-size pipe rack ..???
Do you have specifications or guidelines ??

Which margin is taken for future lines as a general rule ??

Sizing occurs before pipe stress= How can one take into account the axial and lateral loads generated by anchors,Stops, guides ???

Thanks you all !!!!

FATHI.... here's some guidance regarding pipe racks sizing:

W = ( f X n X s ) + A + B.

Where:

f : Safety Factor
= 1.5 if pipes are counted from PFD.
= 1.2 if pipes are counted from P&Id.

n : number of lines in the densest area up to size 450 NB
= 300 mm ( estimated average spacing )
= 225 mm ( if lines are smaller than 250 NB )

A : Additional Width for –
• Lines larger than 450 NB.
• For instrument cable tray / duct.
• For Electrical cable tray.

s : 300 mm (estimated average spacing)
: 225 mm (if lines are smaller than 250 NB)

B : future provision
= 20% of (f X n X s) + A
Generally you use 20% at the begining of Basic Engineering and 15-10% at the begining of Detailed Engineering

Best Regards

[Tiberius]

thanks

[Jiang]

Can you put a link for download?