200,000 psi hydraulic pressure vessel wall thickness?

[Andersonaz1965]

I'm Having a part machined with a cylinder shape approximately 14 inches in length with a cylinder hole in the center with a diameter of .930 . I have no idea how thick the cylinder wall needs to be. I have looked up and used hoop stress calculators online but I do not understand if they take into account the type of material that I am using. I will be using a high-grade 4340 vacuum melt steel. After the heat treating process is complete it will have a ultimate tensile strength of approximately 260,000 psi. I can get the material data sheet listed if that would help. This part needs to be able to withstand a 200,000 PSI working pressure. Any help or direction would be greatly appreciated. Thank you

 

[someguy79]

200 ksi working pressure is immense. I guess that's why you're posting here.

I don't have much for answers, but here are few questions that might steer you toward some helpful tools/info.

What is this thing going to be used for?

Will this thing be load cycled many times?

Are there any special considerations for temperature, chemical reactivity, impact/sudden loading, others?

Have you looked into ASME Code for applicable sections?

You mention an ultimate tensile strength of 260 ksi. Why are you not looking at the yield strength? I would think that's a much more meaningful value to use here. Any yielding might result in a leak, depending on construction.

The strength values might not be consistent throughout the material thickness after heat treatment, depending on the process. Be sure that you're using correct, or at least conservative values.

 

[3DDave]

Typical thin wall hoop stress is based on an idealization that the stress distribution across the section of the hoop is uniform, but if the wall is too thick that won't be the case. I'd suggest getting a stress analyst to look at the situation. In this case, for factors of safety, you would be looking to reduce the stress in the wall to between 50 and 100 ksi which means between 2 and 4 times the total wall thickness as the diameter of the fluid area, which is far outside hoop calculations.

There are thick wall hoop stress calculators, but I'd still suggest running the particular geometry for the entire assembly by an analyst.

If necessary, have a look at the maraging steels. Yields are from 200 to 350ksi. They machine easily before heat treat and change volume uniformly/predictably during heat treat. Being such a wonderful material they have but one major flaw - they are expensive. Still, they are in wide use because their upfront costs are offset by the performance.

https://en.wikipedia.org/wiki/Maraging_steel

 

[3DDave]

Another consideration is the diameter will change due to the pressure, so the seal will have to accommodate that change.

 

[ricklts]

Depending on temperature, use a seal type which is elastically deformed, and mounted as close to the ID of the vessel as possible.

There are may possible designs available, but I would be cautious about the closure mechanism(s)- threaded/breech lock styles will warp/deform, bolted joints will require bolts and increase the size/weight/cost of the vessel.

 

[tbuelna]

This pressure vessel requires some type of sliding seal? Is there actually some form of radial sliding seal that can operate at 200ksi hydraulic pressures?

 

[gruntguru]

One would assume that materials with a yield >200 ksi would be required to seal fluid at 200 ksi.

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