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Handling Stress and Plastics

Handling Stress and Plastics

Handling Stress and Plastics

(OP)
Hi,

I typically design tanks or vessels in aluminum or stainless steel.  However, this design has to incorporate a clear window in the side for viewing.  I’m thinking about using Lexan or polycarbonate but I don’t know how to calculate the allowable stress value for plastics.  The window is 12” diameter and the internal tank pressure will only be 1 psi.

Any help would be appreciated.

Thank you in advance

RE: Handling Stress and Plastics

Without going through a bunch of analysis, I think you should be OK with Lexan at about 1/8 thick. Even better, bulge the plastic slightly for better stress distribution.

RE: Handling Stress and Plastics

Is there head pressure in addition to the approx. 1"? What is the material within and is there safety or economic concern should there be failure. I would start at .250" material and head up from there. You may also want to consider glass. It has a more durable surface (scratch) with excellent mechanical strengths which prove for good sealing.

RE: Handling Stress and Plastics

(OP)
automatic2,

No there is not any head pressure.  The aluminum rectangular vessel will be pressurized with 1psi of air only.  The only safetly concern I have is plastic blowing out under pressure.  I know it is unlikely, but I would like to do the calculations to back it up.  I haven't been able to do the calculations yet, but I think 3/8" thick lexan "should" work well.  

Thanks

RE: Handling Stress and Plastics

In the chemical- and petrochemical industry they don't use PC because of the stess cracking if in cantact with certain chemicals. In most cases they use glass or PCTFE ( Polychloortrifluorethylene ) and this material is stress relieved and specially designed for sight-glasses.
If you want more info please let me know,
Best regards,
Ernst

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