Hello Jeffrey, Seems to me you might want to purchace a fuel tank from Cheddar or Roundhouse. Why reinvent the wheel, so to speak?
>From: "Peter Trounce" <[EMAIL PROTECTED]>>Reply-To: [EMAIL PROTECTED] >To: Multiple recipients of sslivesteam <[EMAIL PROTECTED]>>Subject: Re: Testing fuel tanks >Date: Thu, 22 Jan 2004 10:39:56 -0500 > >Hello Jeffrey, >When I was in the design office using the ASME Section 8 Code, typical >numbers for common pressure vessel steel were: >Ultimate Strength 55,000 psi >Factor of Safety 4 >Therefore Design Stress 13,750 psi. > >The Yield Strength (about 30,000psi) was never used for design. >Factor of Safety of 3 was only used for atomic reactors and other very >carefully controlled constructions. > >Actually the ASME Code is not intended for designing things like our fuel >tanks. Flat sides, silver brazing, brass, bronze, copper, threads, are >hardly touched on. > >It was recognized that the yield strength was likely exceeded locally due to >stress-concentration during the hydro pressire test. But thereafter, it >would not be exceeded in service. >In a refinery, the most highly-stressed vessels are the large storage tanks >(not covered under ASME) and other than weld radiography, only testable by >filling with water. >Cheers, >Peter Trounce. > >----- Original Message ----- >From: "Jeffrey Williams" <[EMAIL PROTECTED]>>To: "Multiple recipients of sslivesteam" <[EMAIL PROTECTED]>>Sent: Wednesday, January 21, 2004 10:52 PM >Subject: 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. > > > > > >
