stiffeners for large pipe subject to vacuum
stiffeners for large pipe subject to vacuum
(OP)
pipe with a D/T ratio of ~90 may be subject to vacuum conditions. The thickness is determined based on a selected stiffener distance.
I plan to select B16.9 fittings which will have the typical under tolerance on thickness of 12.5%.
In one instance the required min thickness for pressure is 0.318" and the min thickness for vacuum is 0.445". The selected pipe is 0.500" NW / 0.490" MW (plate has a 0.01" under tolerance). If I spec the fitting at 0.5"NW the min would be 0.438" (.875*.5)
first question...can a fitting, elbow for instance, 'act' as a stiffener or would the min thickness of the fitting also have to meet the thickness required for vacuum service?
thanks in advance.
Mark
I plan to select B16.9 fittings which will have the typical under tolerance on thickness of 12.5%.
In one instance the required min thickness for pressure is 0.318" and the min thickness for vacuum is 0.445". The selected pipe is 0.500" NW / 0.490" MW (plate has a 0.01" under tolerance). If I spec the fitting at 0.5"NW the min would be 0.438" (.875*.5)
first question...can a fitting, elbow for instance, 'act' as a stiffener or would the min thickness of the fitting also have to meet the thickness required for vacuum service?
thanks in advance.
Mark





RE: stiffeners for large pipe subject to vacuum
Are you sure you need stiffeners with a D/t of 90 for vacuum alone? I don't believe that a vacuum alone is enough to collapse that pipe. If you don't have additional loads on the exterior of the pipe, hydrostatic, etc., I'd have a look at the calculation again.
What would you be doing, if you knew that you could not fail?
RE: stiffeners for large pipe subject to vacuum
48" OD, 0.500" Nominal WALL / 0.490" Min. wall, ASTM A-691, GR 1.25% CR, CLASS 22
I did not do the vacuum calc, but I hear that the stiffener distance used was 100 feet. Perhaps we are too conservative using that distance but that is the value.
so, the question still stands, can an elbow or other fitting act as a stiffener due to their difference in geometry when compared to the pipe?
thanks
RE: stiffeners for large pipe subject to vacuum
I'd urge you to get another opinion on the calculation. There's pleanty of 48" out there without vacuum stiffeners.
What's the product? What's the temperature. What's the rest of the story? Maybe that's got something to do with it.
What would you be doing, if you knew that you could not fail?
RE: stiffeners for large pipe subject to vacuum
The calc's are a pain, as you take intermediate results to a nomograph, then take the nomograph results to a 2nd nomograph. But do them anyway, "numbers don't lie".
SWAG = Scientific Wild-A$$ed Guess.
RE: stiffeners for large pipe subject to vacuum
Anyway, don't matter, put um where you like um, because IMO stiffeners arn't needed. I'll bet that 100 psi external diff pressure would do ... absolutely nothing, never mind 1 barg.
What would you be doing, if you knew that you could not fail?
RE: stiffeners for large pipe subject to vacuum
Is the vacuum a process condition or an upset condition from a waterhammer study? This affects how you approach the design.
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