How to determine pipeline failure ?

[hady511]

Dear Engs,
First thanks to this forum that let us get really an excellent experience.

I want to involve you in my problem, I have a pipeline with following parameters:
- 10 " X 0.365 "
- Temp. Difference (165 C) /between installation and operation/
- Pumped material (Asphalt)
- Line aboveground (920m in length)

If this line restrained from two ends, and i want to analyse it, to sure that its flexible or not, its safe or not<<<<< what should I Do ?

I've used the failure theory (Maximum shear stress) (Tresca) with the following equations:
Sc=2 τmax=√{(Sh-SL )^2+ 4τ^2}
SL = -E×α×∆t + υ ×Sh
Sh = Pxd/4t

OK, Now after doing some calculations and compare Sc with S.M.Y.S its result that line will fail because of the thermal expansion.

Conclusion we must add solution which in my case will be expansion loops,,,,
after adding them,, calculate everything related...

I want to check again the flexibility of the line after the adding of loops,,,,
so if I go back to theory (Tresca)
the result which i'll get is same as before adding loops ???
as all factors in equations above doesn't change !!!!

SO IS IT WRONG TO CHECK THE FLEXIBILITY OF PIPELINE BY THEORY (Tresca) ???

Please Help

REGARDS
Eng. Hady

[DSB123]

Use a proprietary software such as Caesar II, Autopipe,Simflex,Algor, pipepak or even ansys. As you do not fully understand pipe stress analysis then I would employ a reputable Company to do the analysis for you. Also asphalt is erosive I beleive so adding bends for loops should be considered from an erosion point of view. You may need to substantially thicken up the bends.

[hady511]

Use a proprietary software such as Caesar II, Autopipe,Simflex,Algor, pipepak or even ansys. As you do not fully understand pipe stress analysis then I would employ a reputable Company to do the analysis for you. Also asphalt is erosive I beleive so adding bends for loops should be considered from an erosion point of view. You may need to substantially thicken up the bends.

Thanks for your reply, I'll indeed check my calculations on paper by ANSYS and STAAD as other softwares aren't available here in market !!

BUT......
Can't we check the flexibility of this line by calculations without software ????
As the code B31.3 use Tresca theory in determining the failure ???,, also referring to B31.4 and other references books lead me to use above equations to compare the stress with SMYS ??

Any clarifications from your side will be useful for me.

AS for the erosion thanks for this information and i'll take note.

REGARDS

[ECH1]

Have you a simple sketch of the line?
Mark it with expansions and points where the calcs fails for the line.
Maybe you put some arrangements for expansi&oacute;n but they are not enough or the points you choose are not the best.
Rgds.

[hady511]

Let me make a brief check.
Have you a simple sketch of the line?
Mark it with expansions and points where the calcs fails for the line.
Maybe you put some arrangements for expansi&oacute;n but they are not enough or the points you choose are not the best.
Rgds.

Dear ECHI
The sketch is very simple !!!,, its just line with two existing anchors (Pump house from side, and a valve from the other side)

I think you miss my point,, and want to re ask my question again !!

Suppose you have line with asphalt running into it, the route of line as above,,
other parameters I've mentioned them before

HOW YOU WILL DECIDE THAT THIS LINE WILL FAIL OR NOT AS THERE WILL BE 165 C BETWEEN INSTALLATION AND OPERATION ???
then we will go to the next step (SOLUTIONS)

REGARDS

[ECH1]

dl = α Lo dt
where
dl = expansion (m, inches)
Lo = length of pipe (m, inches)
dt = temperature difference (oC, oF)
α = linear expansion coefficient (m/moK, in/inoF)
After replacing you have an expansion of 2290 mm.

If you see the sketch with one straight line the expansion of 2290 mm will broke one of the restrained ends (there is no way to handle this expansion in one straight line).

Look at the line with four elbows, the expansion due to the temperature increment is the same, but if you do the length L enough prolonged, the stress due to expansion could be minimized and Tresca is still working.

Both sketchs are in the Dl. doc file attached.

Regards.