Shearing pressure of 5 pitch stub acme threads.

[edeaster]

I am making a pressure vessel from grade 316 stainless steel.
3" OD X 2" ID X 15" long. End caps are 4"OD X 1 1/2" long.
Threads are 5 TPI stub acme with thread engagement of 4 threads (.800")
Is it possible to shear the threads off with internal pressure allowing the caps to blow off?

Customer is using this at 8000 PSI.

[PinkertonD]

Is it possible to shear the threads off with internal pressure allowing the caps to blow off?

Hi Ed, welcome to the forum.

Yes. Do the Math. The area of the end caps is around 6-sq. inches x 8000-psi = 48,000 lbs.

Dealing with pressures such as this not for the neophyte, people can get seriously hurt. You need to hand this to someone who understand the mechanics of materials at such high pressures.

I for one, willl not be commenting further on this thread. Proceed at your peril.

[edeaster]

I would really like to discuss this with you. Would you consider?

[PinkertonD]

Hi Ed,

Hate to say it but that kind of stuff is way out of my league. The most pressure I have dealt with was 3000-psi and that scared the crapper out of me. Also being a pressure vessel, your project may need Local or National testing and certification. For that you are going to need someone with the credentials to do that. Most (all?) State and Federal jurisdictions take pressure vessels very seriously.

[Kelly_Bramble]

Hi Ed,

Hate to say it but that kind of stuff is way out of my league. The most pressure I have dealt with was 3000-psi and that scared the crapper out of me. Also being a pressure vessel, your project may need Local or National testing and certification. For that you are going to need someone with the credentials to do that. Most (all?) State and Federal jurisdictions take pressure vessels very seriously.

I agree with PinkeronD, moreover this is sensitive liability ground.

Conceptually, it does not make sense to me to design in a thread failure scheme on a pressure vessel.

There are way better ways to ensure safety at excessive pressure. A pressure relief valve is less costly than your NRE and more predictable in a pressure vessel system.

[jboggs]

edeaster,
You may not know this, but you have just gotten feedback from two of the most senior members of this forum. You have been given the benefit of advice from only God knows how many decades of experience there. Take it seriously. I will add my 35 years to the mix. If you proceed with this project without the direct involvement of a professional experienced engineer familiar with both the technology of the field (design of high pressure vessels) AND with the applicable government codes, you are walking into a minefield of disaster. You are entering a field where even the smallest unanticipated situations (like a fault in bolt threads or improper heat treat of materials) can result in an explosive failure with no warning at all. We're talking about major human injury and worse. Do not proceed further without that direct help. If you want help on where and how to find such an individual we can probably help you with some suggestions.

That is the best possible advice you can get from this forum of experienced engineers.

[edeaster]

You are missing the point. I was given the specs for this job and I am asking out of curiosity.
The pressure is being held by a 2" plug with seals which is in turn being held in place with the cap.
Yield strength of 316 SS is 75,000 to 90,000 Lbs.
8000 PSI internal pressure (hydraulic) = 25,120 Lbs. against the cap.
I am looking for a formula to determine how much pressure is required to shear the threads.

[Kelly_Bramble]

You are missing the point.

No, you are.... Sincerely, if you don't know how to determine thread shear strength you should not be taking any resposibility for the design.

Get somebody certified by ASME to provide you with documented calculations and ensure they are certified to ASME Pressel Vessel code.

See: http://www.asme.org/kb/standards/cer...-certification

[edeaster]

Why don't you people just say you don't know the answer instead of hiding behind your engineering
and lawer degrees?
I have determined from another source that the cylinder will burst (40,000 PSI) before the threads
shear (339 tons)

[Kelly_Bramble]

Why don't you people just say you don't know the answer instead of hiding behind your engineering
and lawer degrees?

There are not less than five WebPages on this very website that have equations and will even calculate what you are looking for.

NOTE: Engineers Edge assumes no liability or guarantees about the accuracy - the user should verify and use at own risk.

What you're not getting is that pressure vessels are serious business. There is a reason why there are certifications, PE’s and pressure vessel codes.

When Pressure vessels fail at 8000 psi + people die, property is destroyed, huge sums of money is lost and lawsuits are initiated.

Seriously – get the right people involved whom are experienced in pressure vessel design, engineering and code on this one…

Good luck...