Pressure vessel design reality check

[Jimmer12]

Hi everyone,

I am looking for a quick reality check. I have some background in pressure vessel design, but we always used APV for calcs, and only worked up to 150 psi. Well I have had a friend ask me to design a one off filter unit for him, to handle 5000 psi, and was hoping to get a quick look over my wall thickness calcs.

I am using the formula t=p*Ro/(Stress allowable + 0.5p)

Using 5000 psi
3.5" OD
SS 316 with a UTS of 80,000psi
FOS 4

I am getting 0.389" wall thickness.

Can anyone comment on my calcs and let me know if I'm making sense?

Thanks,
Jim

 

[MJCronin]

Jimbo....

When I use the rules for B31.1/B31.3 piping design, with an allowable stress of 20,000 (no corrosion/threading allowance etc) I get almost the same number.

Why are you not using the rules of ASME VIII ?

 

[jamesl]

Your calulation result is correct. However, if you use pipe (based on 3.5" OD you used), you need to add 12.5% undertolerance.

If you use ASME Div 1, the forumla to use shall be the one for heavy wall. However that does not change the results much.

 

[Jimmer12]

Thanks guys.

MJ, I'm not using Sec VIII, because I am no longer working in the pressure vessel industry and don't have a copy of it. Also, this being a one off design, that isn't being used for commercial use, or being sold, I have no requirement to follow any specific code. It's for a scuba compressor, and most other HP air products I have dealt with have used 4:1 FOS, so I felt pretty comfortable with that, especially being made from SS, rather than the aluminum that most filter housings are made, I am not too worried about sustained load cracking or fatigue..

James, you are correct it is based on pipe, and I am looking to use 3" XXH which has an OD of 3.5" and wall thickness of 0.6", so there is plenty of room for tolerance issues. I am planning to thread the pipe internally, and turn SS end plugs using O-Ring seals, and obviously use the correct OPV and associated plumbing.

 

[Duwe6]

Would have been easier to check ratings of pipe using a good Pipe Spec. Sch 160 s/s is more than adequate for 5000 psig. XXS may be hard to find, and is 'overkill', as your calc's have shown.

 

[JStephen]

I suspect scuba gear might use a lower factor of safety than Section VIII pressure vessels.

 

[Jimmer12]

You may be right, there is virtually no welded seam pressure vessels in the scuba industry. Everything I've seen has been seamless with O-ring seals.

I think I will continue with my design using Sched 160. I had originally thought XXS might be good, because I have to thread the tube, and it is being used in a moisture separator so it will have the potential for corrosion as well.

Jim