Maximum Allowable Vacuum for Pipe

[mrsongs]

I'm looking for the maximum allowable vacuum in standard 18” and 24” Sch10 316SS pipe. Is there a reference I should be looking for our a formula to be used?

 

[BigInch]

The calculation is described here,

http://www.pipingoffice.com/pdf/ExtP.pdf

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[racookpe1978]

well, yes that's the calculation for an imposed outside pressure on an unstiffened pipe, but in air (atmosphere - if I'm reading the original poster right) can you get below the vacuum of a standard power plant condenser - only few inches of water (er, vacuum) is not comparable to the pdf file's several hundred bar pressures? ...

Much more than the "inverse" of 14.7 psig, but still

 

[BigInch]

We usually do not consider any gage pressure inside (0 psia) as outside pressures from soil or ocean water pressure make the contribution from -atmosphere relatively insignificant, additionally thinking that someday the pipe internal product pressure could easily be reduced to near 0 psig for maintenance or tie-in purposes anyway.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[ione]

For thin wall pipes (and you are in this condition) Tresca’s criterion leads to

Sigma adm>= |Sigma hoop| = (Pe * r)/s

Pe = external pressure
r = pipe radius
s = pipe thickness

As already stated by BigInch I would take into account only external pressure.

Please consider that temperature and consequently thermal expansion could play a non trivial role.

 

[rconner]

fyi

http://www.eng-tips.com/viewthread.cfm?qid=191919&page=97

(I believe most collapse failures of working pipelines associated with negative pressures have generally been with quite large, high D/t ratio pipelines; however, quite thin SS pipelines are being promoted in even smaller sizes due to basic alloy/material cost and at least a perception that they are not vulnerable to corrosion. It should probably also be noted buckling resistance can be much reduced when there are high localized stresses or ovalling etc. deformations for whatever reason)

 

[stanier]

ASME B31.3 and AS 4041 all cover the external pressure calculations.

If the pipe is buried then standards such as AWWA M11 or AS 2566.1 need to be considered.