Testing fuel tanks
I'm concerned that there is an impression out there that there exists some standard or traditional test pressure that is correct for all fuel tanks or other pressure vessels (including boilers). Various numbers like 350 psi or 160 psi have been proposed. My recently purchased Accucraft 3-cylinder Shay came with a certificate which claims that the butane fuel tank was tested to 160 psi. There is an old adage in mechanical engineering that says "you can't test in safety" - or maybe it's an adage of old mechanical engineers - I can't remember! The safety of a system comes from its design, including dimensions, material selection, joining techniques, reinforcing details, penetrations and a host of other factors, not from one "proof" test. Testing of a system can be done to verify analysis done in support of the design, but a vessel that is tested, intensionally or accidentally, to stress levels above the yield strength of even one of its components is not a safe vessel, because the test has already caused the material, joints, reinforcements and/or penetrations to plastically deform and become unsafe. The only possible way that pressure testing "guarantees" safety is if a manufacturer is willing to subject a very large number of identical vessels to a test-to-failure to gather statistics that also support the original design limits of a vessel. Yes, it is possible that a single pressure test, if improperly defined and carried out can in fact decrease safety, rather than ensure it. The ASME Boiler and Pressure Vessel Code has been around for almost a century in order to bring science (and safety) to pressure vessel design, testing and operation. The Code not only defines acceptable methods of design and construction, but also material selection, joining, repairing, inspection and testing. University engineering libraries will have a copy of the Code if you are interested or you can buy it from ASME for a very large sum of money. Pressure vessels are designed with a "safety factor" in mind (often a minimum factor of 3) to the yield strength of the materials used in construction of the vessel. In other words, at maximum operating pressure and temperature, every part and component of the pressure vessel will experience stresses of no more than 1/3 of the yield strength of the material at that temperature. Other safety factors may be chosen for different applications, depending on the consequence of failure and the precision with which the designer knows the as-built dimensions and material properties. There are lots of subtleties like fracture toughness, stress concentrations, anticipated future loads, damage or corrosion and low-temperature transition temperatures, etc. that can also bite you if you're not careful. It's my suggestion that people who do not have training and experience in "strength of materials" calculations be incredibly careful when embarking on the design and construction of any pressure vessel whether it's a fuel tank, boiler or other vessel. Make friends with a trained mechanical (or sometimes chemical) engineer so that he or she can review your design and your fabrication and testing plans. The live steam fraternity has plenty of us mechanical engineers who are attracted to the hobby because of its application of very pure and basic engineering principles, so you should be able to find someone of appropriate background who would be happy to review your pressure vessel design. And please, if you feel very confident in your own analytical ability, review a copy of the ASME Code and get a copy of "Formulas for Stress and Strain" by R.J. Roark before you inadvertantly build yourself a bomb.
RE: Butane/Propane Fuel tank Pressure?
Maybe, I do have a PMR boiler feed hand pump which I use for hydro testing so it might just get that high. Though I would hate to go to that high of a pressure and end up yielding the material when it would not be an absolute necessity. Steve > -Original Message- > From: Peter Foley [SMTP:[EMAIL PROTECTED] > Sent: Wednesday, January 21, 2004 12:17 PM > To: Multiple recipients of sslivesteam > Subject: RE: Butane/Propane Fuel tank Pressure? > > At 09:08 AM 1/21/04 -0800, Steve Ciambrone wrote: > >I do not think I can test to the 350 Psi Mike recommended. 160 PSI might > be > >a good compromise it is three times working pressure of butane at 120F > and > >twice the working pressure of an 80/20 mix at 90F. I was planning on > >building my tanks out of 1 1/2" copper pipe with end plates the same as a > >boiler. > > You would be surprised what you can get out of a hand pump squirty > bottle! We've had one run up over 300 psi somewhat by accident - it was > taken out to the local model engineering society to show how simply small > boilers could be tested. It was left out after demonstrating a 150psi > test. they kept squeezing the trigger and took it over 300. No damage to > > anything, either. give it a try. > > regards, > > pf >
RE: Butane/Propane Fuel tank Pressure?
At 09:08 AM 1/21/04 -0800, Steve Ciambrone wrote: I do not think I can test to the 350 Psi Mike recommended. 160 PSI might be a good compromise it is three times working pressure of butane at 120F and twice the working pressure of an 80/20 mix at 90F. I was planning on building my tanks out of 1 1/2" copper pipe with end plates the same as a boiler. You would be surprised what you can get out of a hand pump squirty bottle! We've had one run up over 300 psi somewhat by accident - it was taken out to the local model engineering society to show how simply small boilers could be tested. It was left out after demonstrating a 150psi test. they kept squeezing the trigger and took it over 300. No damage to anything, either. give it a try. regards, pf
RE: Butane/Propane Fuel tank Pressure?
Thanks for the tips Mike and Jeff. Since the data provided varies I will probably use a pressure somewhere in the middle, since I can buy straight butane a lot cheaper than the 70/30 mix, I live in Southern California and any temperature below 60 F is too cold to run trains anyway. I will test to run butane with margin and then only use a mix if required on cold days. I do not think I can test to the 350 Psi Mike recommended. 160 PSI might be a good compromise it is three times working pressure of butane at 120F and twice the working pressure of an 80/20 mix at 90F. I was planning on building my tanks out of 1 1/2" copper pipe with end plates the same as a boiler. Thanks Steve > -Original Message- > From: Jeffrey Williams [SMTP:[EMAIL PROTECTED] > Sent: Monday, January 19, 2004 4:57 PM > To: Multiple recipients of sslivesteam > Subject: Re: Butane/Propane Fuel tank Pressure? > > See "Notes from the Unit Shop": Kevin O'Connor's advice for the > beginning small scale live steamer > > http://www.southernsteamtrains.com/notes/bestfuelgas.htm > > Kevin provides pressure vs temeprature for a number of gases and mixtures. > > = > > > > Ciambrone, Steve @ OS wrote: > > I am considering building a fuel tank for my ruby and other engines > large > > enough that I do not have to stop during a run to refuel, I find it far > more > > difficult to keep the fuel from running out than the water. > > > > Anyway what is the Maximum working pressure for a 30% Propane and 70% > butane > > fuel mixture (Primus)? I would perform a hydrostatic pressure test at > > twice the working pressure on the finished tank. > > > > Thanks > > Steve > > > >
