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thin walled tube

thin walled tube

thin walled tube

(OP)
Is the calculation for tube thickness with a negative internal pressure the same as for posative internal pressure(pd/f). Can't remember this one and all texts only do formulaes for posative internal pressures, nothing showing an external pressure.
 Cheers
Mick

RE: thin walled tube

(OP)
sorry pd/2f

RE: thin walled tube

Try to find API Bul 5C3; it will have collapse calcs.

RE: thin walled tube

Hi,

This formula is the same. The p is just the pressure difference. Fact is though, that you will have to check stability against imploding as well. For this a different criterium is necessary. I haven't got that in my active mmemory, but you should check a technical handbook or the internet on that. In german the term is "beulen" in english I do not know.

Karel Postulart, The Netherlands
Nuon Power Generation

RE: thin walled tube

In Americanese, we'd call it buckling.

RE: thin walled tube

API Bul 5C3 has all 4 modes; tensile, burst, buckle and collapse (2 methods depending on D/t ratio). Does Barlows' formula have a new name?, It is hard keep up with technology.

RE: thin walled tube

(OP)
Thanks for the replies. my "tube" is actually ducting 300mm dia with an negative internal pressure of -0.3bar. A bit bigger than the API piping specs.

RE: thin walled tube

See API-RP-1111 Design Construction Installation and Maintenance of Offshore Pipelines - Section 4.3.2.1 Collapse Due to External Pressure. (Use absolute pressure and positive external pressure is physically the same as negative internal pressure).

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us.  Lisa Gansky

RE: thin walled tube

It seems that API is your standard, however, AWWA M11 "Manual-Steel pipe Design and Installation" has a full coverage of buckling calculation for circular cylindrical shells under external loads, buckling.  

RE: thin walled tube

API 5L goes to 2032mm diameter; The 5C3 strictly speaking only applies to API casing/ 508mm max.

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