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Question: Thin Walled Cylindrical Vessels

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CVesGuy

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Question:

I work in a small sheet metal shop. We make cylindrical vessels (up to 4 ft in radius) that can hold up to a few psi.


The usual formula I use - which was given to me by the chief engineer - for wall thickness is PR/t=stress (Hoop stress) or t=PR/Allowable stress at temperature.

I then throw in about 40-60% extra thickness for a margin of error.

Do I have to add in axial stress (PR/2t) [which is perpendicular] and/or shear?

My understanding is that since hoop stress is the largest, it alone is sufficient.

This is not an ASME shop.

My understanding is that you do not add the hoop, axial, and shear stresses, but but go for the maximum, which in our case is hoop stress.
 

Lumber Jim

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Question:

I work in a small sheet metal shop. We make cylindrical vessels (up to 4 ft in radius) that can hold up to a few psi.


The usual formula I use - which was given to me by the chief engineer - for wall thickness is PR/t=stress (Hoop stress) or t=PR/Allowable stress at temperature.

I then throw in about 40-60% extra thickness for a margin of error.

Do I have to add in axial stress (PR/2t) [which is perpendicular] and/or shear?

My understanding is that since hoop stress is the largest, it alone is sufficient.

This is not an ASME shop.

My understanding is that you do not add the hoop, axial, and shear stresses, but but go for the maximum, which in our case is hoop stress.
I think you and your chief engineer should find the appropriate industrial standard for the application and use it after you get comfortable and confident with it or find someone like me that provides those services.

I wouldn't expect more detailed guidance here than that based on what you have described but maybe I'm wrong...

Just because you are not an ASME shop doesn't mean you can't use ASME.

"Designed in accordance with..."
Or
"Certified to..."

Insert the appropriate design code or standards after that.

I've seen plenty of low pressure thin walled vessels blow the roof off service shops and design ALWAYS comes into question.

CYA
 

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