Calculating side wall thickness based on psi requirement

[MtnEquip]

Right up front I'm not a mech. engineer. I need to order some forged tubes that will eventually wind up as cylinders. The cylinders need to handle 6,000 psi (MAWP). The sales guy at the forge wants the desired thickness of the sidewall, and I'm not certain how to calculate that. From what I can tell I need to hire an engineer, but for the purposes of getting an estimate, that seems like a lot of expense. Can anyone direct me to a web resource that will help me calculate the necessary wall thinkness for ASME using ASME SA-105 2004 Edition, 2006 Addenda forged steel? Thanks for your ideas.

 

[JStephen]

For a rough estimate, take inside radius times design pressure and divide by allowable stress. For mild steel, that would give you wall thickness about a 35-40% of the radius.

It actually gets more involved due to the ASME formulas including allowance for stress variation through the thickness.

You don't say what your application is, but actual stress used could vary quite a bit. The pressure vessel codes tend to be conservative, due to the failure of a pressure vessel being a lot like a bomb. Something like a hydraulic cylinder usually isn't quite as hazardous. Something like gun barrel, maybe more so. And you could have some considerable variations in the design due to uncertainty in the pressure, operating temperature, fatigue, actual material, etc.

 

[gr2vessels]

Mtn,

Please give us some details, like inside diameter, the fluid you'll see inside those forgings, perhaps the operating temperature the forging will see. We'll try to help.
Cheers,gr2vessels

 

[MtnEquip]

Thanks for helping me zero in on this. The vessel will be handling natural gas right out of the wellhead in a flow-thru state; no storage -- in one end, out the other. Typically the gas will be anywhere from 30c degrees up to 400c; it depends on the depth from which it is recovered.

The inside radius of the vessel is 8". I found a web site (

http://www.red-bag.com/engintools/wallthickshell.php)

that provides a wall thickness calculator, and using that I sorta muddled thru, but I can't say I have any confidence in my result. My main problem is that I'm not sure how to define all the required variables (I'm a software guy by training.)

 

[pmover]

MtnEquip,

It is best and recommended that you hire a qualified engineer to determine the equipment parameters (wall thickness) for the fluid process conditions (pressure, temp, & fluid composition) so desired. Risk and liability are far too great to undertake/accept; especially in the event of failure. Trust me, it is far cheaper and less risky on your part to hire a qualified engineer than to obtain results by yourself.

I applaud your efforts and desire for learning. But in today's society, it is far too risky.

good luck!
-pmover

 

[MtnEquip]

Pmover, I'm coming to the same conclusion. Which of course begs the question, how does one find an experienced engineer for this type of job?

 

[vesselguy]

MtnEquip,

I suggest you hire a local "head hunter" to find you an Automotive Engineer. Sounds like your project is related to automotive rather than with boilers and vessels, right? These people will have a large database of Engineers and I'm sure they can help you hire someone for a fee.

Alternatively, if you want to save some money and do it yourself, you could contact your local Professional Engineer regulating body and they may be able to help you as they have a complete database of registered PEs in your State.

Just remember that you should never do engineering from free engineering advice like on a board like this. You can get "advice" but not the real engineered solution that you can hang your hat on. To do that, you hire a professional.

 

[CreativeVessel]

While ASME Section VIII Division 1 has no formal pressure limit, they recommend pressures be <3000 psi. As mentioned in previous replies, the rules for thick cylinders differ quite a bit from thin shells.

With the basic conditions given (8” radius @ 6000 psi), you would be looking at a thickness ~3” thick + corrosion allowance. As an alternative Division 2 can be used which would reduce the wall thickness by ~ 20% (to ~ 2.5” thick).

There are many variables which would increase the wall thickness beyond these approximations and a professional engineer should be retained.

Regards,
CreativeVessel