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simple pressure vessel question ... I think

simple pressure vessel question ... I think

simple pressure vessel question ... I think

(OP)
I plan to make a very small pressure vessel using some thick wall pipe I found online. It's 4140 steel and 2.25 inch wall. The caps will be machined with a slip fit and two oring grooves and o-rings with back up rings. Working for an o-ring manufacturer, I know the cap and seal part of my design is sound. My question: will a 6.25 inch ID pipe, 14 inches long handle a static pressure of 4800psi? My calculations say yes (in fact should hold 10,000psi), I just need a quick confirmation. Keep in mind this is only for lab testing of parts to check operation in subsea conditions.

thanks in advance for any help.

RE: simple pressure vessel question ... I think

Actually - it starts off as a very difficult question. And it all depends on where this pressure vessel will be located - there are local laws the define if and when a pressure vessel must comply with appropriate Codes and Standards. So, where will the pressure vessel be located?

RE: simple pressure vessel question ... I think

The piece of pipe doesn't worry me, it will handle the pressure, but exactly what its max pressure is depends on which design code you use, 31.3, 31.4 or 31.8 depending on what's in it and where it is.

However everything else about this question worries me. How are the caps secured? Is it subject to any heating or just pressure? Are there any nozzles or other attachments or forces? Why do you call this a pressure vessel when it sounds like a bit of pipe?, how will you test it to make it safe to use? Who is authorising this activity? How do you actually know what you've got - was the supplier reputable and do you have material certificates? I think you can see where I'm going here....

If this goes horribly wrong and at 331 bar its no trifling matter you could easily kill someone. Please get sometime who is qualified and experienced to design this and certify it.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: simple pressure vessel question ... I think

Also I looked up 4140 because it wasn't familiar to me and it appears to be a high strength steel (SMYS 770 MPa), normally used for shafts, structural compnents etc and is not a normal pipe / pressure containing material.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: simple pressure vessel question ... I think

As LittleInch confirmed, your wall thickness is adequate.

In test environments in the USA 4140 is often used for applications as you described. The material is strong, machinable, and readily available.

It is a very good idea to have your design conform to a design code and with a little effort it is not that difficult. You really should document your design with BPV Sect 8 Div 1 calculations as a minimum or the applicable equivalent local standard.


Best of luck with your tests…

RE: simple pressure vessel question ... I think

In excess of 3000 psi and small diameter, I would think that ASME Section VIII Div 3 would be applicable.

RE: simple pressure vessel question ... I think

Thanks for the correction fegenbush...

RE: simple pressure vessel question ... I think

(OP)
Thank you for all the input.

No, 4000 psi is not a trifle. However, it is when you compare it to the 30,000 I often test to.

You'll have to trust me that every other part of this test fixture is designed and constructed using quite safe practices. The testing will only be performed by me in a lab environment.

I just needed a sanity check on the pipe.

Kind regards,

Kind Regards,
Skip

RE: simple pressure vessel question ... I think

Quote (thatismytruck)

You'll have to trust me that every other part of this test fixture is designed and constructed using quite safe practices.
Would those practices be in accordance with the laws and ordinances of your local jurisdiction?

You're new here - in these parts we use the motto of the Apollo Program "In God We Trust - all others bring data".

Without information on the temperature of the test and the Code of Construction, there's no "sanity" check. Depending on the Code of Construction, 4140 may not be a permitted material - due to ductility issues.

Will you cycle the internal pressure ever?

RE: simple pressure vessel question ... I think

With my limited knowledge and experience, I have never see a 4140 pipe, is this a hollow shaft machined from a solid bar?

To your question, I don't think the hoop stress by pressure is a problem for given wall thickness, but designing a pressure vessel is more than just considering hoop stress.

Regards

Spoonful

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