NPT Fitting Pressure Limits
NPT Fitting Pressure Limits
(OP)
I have a simple pressure vessel, and am looking for guidance on calculating the safe working pressure. The vessel consists of a 3/4" schedule 80 red brass pipe with a red brass cap on one end and a mechanical pressure gauge on the other end. Fittings are NPT with Loctite 565 sealant. I plan to put dry ice in it and cap it, raising the pressure to about 1000psi of Co2. I get an SF of around 8 for the hoop stress. Are there any other bursting/safety issues that I should consider? If so, what is the proper methodology for rating the pressure of this design?





RE: NPT Fitting Pressure Limits
RE: NPT Fitting Pressure Limits
I have strong reservations about pressuring an unknown tank with gas (rather than water) since the reserve energy of high pressure gas is significantly more dangerous than water. If the tank bursts, then the excess pressure is quickly relieved. Not so with gas.
Frozen CO2 pellets to take up volume? What about the tank and piping strength at that reduced temps?
RE: NPT Fitting Pressure Limits
racookpe1978 - this is an existing design. Just an 8 inch nipple, cap, and gauge. As noted I need to upgrade the fittings to a higher rating and then should be good to go. I just have not had any previous experience with very high pressures and it was making me a little nervous. Looks like it is as simple as specifying a purchasing the proper components.
RE: NPT Fitting Pressure Limits
RE: NPT Fitting Pressure Limits
It just hasn't hasn't killed anybody yet.
RE: NPT Fitting Pressure Limits
Anything else is just guessing with a REAL bomb.
RE: NPT Fitting Pressure Limits
When you calculated your SF, did you deduct for the thread depth, mill tolerance, or corrosion allowance?
RE: NPT Fitting Pressure Limits
RE: NPT Fitting Pressure Limits
stand behind the fat guy. experience with the type of pipe/fittings you have described has shown a vast tolerance in the threading. Have you actually measured the threads on the end caps and mating pipe ends? If they were roll cut, work hardening could take place and increase brittleness in that area.
good luck
RE: NPT Fitting Pressure Limits
Is there something that prevents you from pressure testing your proposed vessel ?
I would pressure test to 1300 to 1500 psig or...
If you have enough $$ break a few of them, and, as suggested above, divide the average failure pressure by a generous factor, write a report and proceed with confidence.
Testing trumphs analysis.....
RE: NPT Fitting Pressure Limits
Patricia Lougheed
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RE: NPT Fitting Pressure Limits
RE: NPT Fitting Pressure Limits
rmw
RE: NPT Fitting Pressure Limits
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: NPT Fitting Pressure Limits
if ambient temp your 3/4in pipe and fittings(pipe not vessel) will withstand
3000 to 5000 psi.
RE: NPT Fitting Pressure Limits
Cheers,
gr2vessels
RE: NPT Fitting Pressure Limits
Actually, not an entirely bad idea. Madam Moderator -- thoughts?