Plastic vessel buckling under external pressure

[sreasoner]

I am designing a plastic vacuum container, approximatly 10 inches in diameter. Does anyone know where to find anylitical formulas that can predict the buckling pressure.

Thanks

 

[MJCronin]

sreasoner,

The formulae for evaluating metallic pressure vessels under external pressure is contained in ASME Section VIII.

A theoretical discussion of the mechanics of cylindrical buckling under external pressure can be found in books on pressure vessels by John Harvey and Henry Bednar ( see AMAZON and/or your local university library) Your problem, as you probably already know, is that you are dealing with plastic materials.....

For small diameter metallic vessels (like you have) protection to "Full Vacuum" causes no additional cost

I suggest that, rater than an analytical approach, you contact some lab or facility that can test the components to twice the external pressure that you desire. Base your design on successful models......


MJC

 

[bvi]

Since your vessel is plastic, the problem is more complex. Plastic typically creeps, even at room temperature, so you have a time dependent buckling problem, in which creep response is a consideration. The is a paper from many years ago by Donald Griffin, Inelastic and Creep Buckling of Circular Cylinders Due to Axial Compression, Bending, and Twisting wherein secant and tangent modulus from isochronous creep curves are used to predict time dependent buckling. This could be used for guidance. The formula for creep buckling of a cylinder due to external pressure is stresscritical=((EsEt/(3(1-v^2)))^0.5)*t/r where Es is secant modulus, Et is tangent modulus, t is thickness, r is mean radius, and v=0.5-(0.5-Poisson's ratio)Es/E, and E is elastic modulus.

The difficulty will be establishing the tangent and secant modulus. An appropriate factor of safety would also need to be applied.

 

[prex]

ASME B31.3 has a chapter on nonmetallic piping, but for external pressure there are no rules, except that the design must be based onto operational experience or performance tests extended over the full design life of the component.

prex

http://www.xcalcs.com

Online tools for structural design

 

[johnnymist2003]

Hi sreasoner,

look at BS 4994. This is a code for designing reinforced plastic tanks and vessels. It may provide you with some guidance.

John