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pipe with external pressure, collapsing pressure = ?

pipe with external pressure, collapsing pressure = ?

pipe with external pressure, collapsing pressure = ?

(OP)
I've got a long pipe which has in a certain section, a certain external pressure.

t/R <<< 1/10 so thinwalled pipe.
diameter = 0.4 m

I cannot scan a drawing here, but imagine a long pipe in which a section of 2 meters is used for heat transfer. So the pipe is surrounded for 2m by steam with pressure > internal pressure of the pipe.

What is the critical, or collapsing pressure?
Roark's 6th ed. says (p. 634): q' = t/R (sigma yield)/[(1+(4 sigma yield / E)) * (R/t)²]

Would this formula be applicable in this case?

This formula did not give a solution in the order of magnitude I expected.

Is this case 1c from table 28? (it says, ends capped, however this is not the case), but I cannot find a case that is applicable to this particular situation.

Many thanks for your insights...

RE: pipe with external pressure, collapsing pressure = ?

For a "long" pipe the end conditions probably do not matter.  Collapse will be circumferencial, not longitudinal.  The caps on the end would stiffen the pipe locally, but that effect won't be felt, say, 10m away from the stiffening element.

I don't have Roark's handy, but I bet your design code addresses it too.

ASME BPVC Section VIII Div 1 UG-28 -29 and -30 for example.

- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered.  It is offered with the understanding that the author is not engaged in rendering engineering or other professional service.  If you need help, get help, and PAY FOR IT.

RE: pipe with external pressure, collapsing pressure = ?

Google for:"buckling pressure Den Hartog Bednar"

RE: pipe with external pressure, collapsing pressure = ?

Steve ... are you sure about the failure direction for a long pipe ? Maybe terminology, but the simplest external pressure collapse is usually a bilobal running buckle failure that progresses along the pipe until an arrestor ring or flange etc. is reached. I would call that a longitudinal failure.  

RE: pipe with external pressure, collapsing pressure = ?

The failure progresses along the longitudinal axis, but it's due to circumferencial stress.  That's a better way to express things I suppose.

If I pump all the air out of a 2L soda bottle, the "bilobal running buckle failure" sucks the round section in on itself rather than the base of the bottle up to the top.

Same way with internal pressure: circumferencial stress opens a longidutidinal crack.  If I were to predict this failure, I'd find the hoop stress not the longitudinal stress.

Sound better?  I think we're thinking the same way but I'm just confused on terminology (again).

- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered.  It is offered with the understanding that the author is not engaged in rendering engineering or other professional service.  If you need help, get help, and PAY FOR IT.

RE: pipe with external pressure, collapsing pressure = ?

I would use the ASME calculations for vessels under external pressure the distance between circumferential stiffeners is critial.   

RE: pipe with external pressure, collapsing pressure = ?

(OP)
it appears my previous reply didn't work (or maybe I put it in the wrong place)

2nd try:


Steve: thanks for your replies however I'm doing this to do a friend a favor. I do not have any codes available as I'm currently working in a mechanical (metals and welding) engineering business.


ione thanks for your reference, I found a book "Piping and pipeline engineering" by Antaki with the formula I needed, which gave an answer I believe to be correct.

another question: does anyone knows where I can find the E (modulus of elasticity) in function of the temperature (150-200 Celsius, which is 300-400 Fahrenheit) for stainless 304 ?

RE: pipe with external pressure, collapsing pressure = ?

http://www.bssa.org.uk/topics.php?article=139

- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered.  It is offered with the understanding that the author is not engaged in rendering engineering or other professional service.  If you need help, get help, and PAY FOR IT.

RE: pipe with external pressure, collapsing pressure = ?

(OP)
Exactly what I was looking for - thx for that.

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