Handling Stress and Plastics

[rebel]

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

 

[insideman]

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.

 

[automatic2]

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.

 

[rebel]

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

 

[buut]

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