200,000 psi 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

 

[tbuelna]

The biggest problem you face is the stress situation at end connections of the cylinder.

 

[Jughandle]

Your 2nd and 3rd sentences are somewhat contradictory. How can you have done the online calcs without plugging in dimensions? Besides, does the math care about what material you use? Lastly, the high UTS offered by 4340 VAR is not the end-all and be-all; be mindful of fracture toughness and critical flaw size. You might also look up 'leak before break' criteria. (200 ksi is up there. I think you are into autofrettage territory.)

 

[metengr]

The hoop stress you calculate is compared to either one of two stress values - an allowable stress or remaining below the specified minimum yield strength to avoid deformation.

 

[EdStainless]

For this pressure you cannot use a simple Barlow's formula for stress, you need to correct for the thick wall. There are calculators out there that so this.
And any calculation has to use the strength of your material.
Not only should leak before break be a concern, but what safety factor do you need?
In simple service usually 3.5x is the minimum that anyone would use (this means that your calculation using the UTS should result in a theoretical burst pressure of 700,000psi). If the materials involved are hazardous to toxic then a higher safety factor is warranted.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Maui]

Why is your working pressure so high? What purpose will this serve?

 

[Andersonaz1965]

Thank you all for your support. Your response has been very kind. Please allow me one more day to get more information together to better explain what I am trying to accomplish. I am 56 years old with a high school diploma. I have a working shop where I tinker around with a large drillpress and a small mill and layth that I got from Harbor freight. Four years ago I had an idea. and last year I built my first working prototype. And it has broke long-standing records. I am now in the process of trying to make a better looking and functioning package. The truth is I really don't know how much pressure I am dealing with. Probably more at the range of 75,000 to 150,000 psi,I just know that it is one hell of a lot of pressure. The current working part in prototype form has the .930 hole in the center of it. With 2 1/2 inches of solid mild steel surrounding it. It has been through over 100 cycles and has not shown any signs of failure. So I am just trying to make that part smaller. I have always operated this device from with in a steel reinforced concrete wall. I fully understand the dangers of working with these types of pressures. And would never put myself or anyone else in harms way. I thank you all once again for your kind insight and help with this project. Thank you all

 

[gtaw]

I hope we hear from you again. This sound interesting.

Best regards - Al

 

[TGS4]

At those internal pressures, you really need to design to ASME Section VIII, Division 3. Application of that Code requires substantial expertise and experience. I can guarantee that whatever online calculator you used is wrong.

Design margins are specific to high pressure - the 3.5 that EdStainless mentioned is incorrect for Division 3 - it's actually 1.8 on ultimate.

 

[boo1]

can you post a picture of the original vessel?

 

[MintJulep]

Good intentions aren't enough to keep people safe.

Pay someone like TGS4 who knows what they are doing to design this properly.

 

[TGS4]

One other thing, I don't know where in the world you live, but most places in North America have legal requirements to follow the ASME Code. Not doing so could leave you liable for legal repercussions, and if/when your contraption kills someone (and you're not designing to the Code), then you could face criminal prosecution in addition to substantial civil proceedings. Oh, and your insurance probably won't cover you, because you broke the law.