Boilers

[JJG Koopmans]

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Download pressure on my firebox is easy to calculate: the firebox is 10" x 11" open to the air. 110 sq inches x 100 psi is 11,000 pounds.

I have 32 vertical stays, 1/2" in diameter

11,000 / 32 = 345# / stay (round numbers here)

area of stay is .2 sq inches (round number) = 1800 # / stay x 6 for safety = 10,000 psi. Plenty of space for corrosion.

So, assuming NO support from the non-vertical stays and nothing from the mud ring, how much would the firebox move as a result of down-load only, assuming A36 Steel?

I am looking for an answer here from someone that wants to join in.

I don't have my books with me (and I don't do it for a living any more), so I am not going to put my 'rememberences' in print to be shot at.
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Hi Bill,
Being a retired naval architect I synpathise with your last remark! However looking at your example of the load on the firebox, isn't it that there is also a load on the boiler shell meaning that the vertical (and horizontal stays for that matter) are carrying twice the load? They are loaded at both ends.
As an example, I can follow your approach, however it seems to describe a sequential catastrophic failure mode, and, if anything, experience in other fields taught me that real life failures act differently than originally imagined.
As for the strength calculations, there are cheap and very functional student versions of finite element methods (FEM) available. Isn't anybody tempted to try one of these?
Kind regards
Jos Koopmans

[Fred_V]

i run my calculations using the spread sheet from:
http://calslivesteam.org/calboil1.htm

i'm sure many of you have looked at this. is it a good and usable method?

[Fred_V]

The girders on the top of the crown sheet are .375" x .750" x 7.00". The amount of pressure to bend the girders, distort the crown sheet and bend the stays is much more than what is generated. The second reason why we went went this design is that the throttle body lies right in the center of the crown sheet. I am not saying it is a stupid idea putting stays on the crown sheet, just not neccessary in this application. How many Allen Model locomtives are out there and are built to Gene's specifications, quite a few. Have any had catastrophic failures? No.

my Allen Chloe drawings called for girder stays but the dwg. placed them on the flat top of the firebox.

did your dwg. put them off to the side like that? did you need that much room for the throttle?

[jessebanning]

I just sent Chris a few photos to post for me. The boiler drawing for the CP173 is from RRSC and is for a copper boiler using. We used 5.500" DOM with .250" wall and has an OD of 6.00" and has been honed for use in hydraulic cylinders. The real larger section is 7.500" OD with .312" wall. I have the Material Test Report for the rear tubiing and is as follows: Yield psi is 75700, the tensile psi is 95900 and it has a bunch of other specs on it, I'll send that to Chris also so he can post it for me. After welding the boiler it has been normalized taking the stress out of things. The throttle design is slightly different from the RRSC design. It is slightly large in size. The stays are on 1.00" centers and have 2 rows of 7 per side and are .375" in diameter. I also built a boiler for a 1.5" 2-8-2 and has similar construction and was built to the locomotive designer's (Dick Thomas, former IBLS president)specifications.

[Russ Hanscom]

Bill,

The answer to your first question is just the unit load divided by the modulus of elasticity, which for your example would be 1800 divided by 29,000,000 equals .00006 inch of stretch per inch of length. Note that the modulus of elasticity is pretty constant regardless of the grade of steel. Not much and there are lots of other little deflections going on too!.

I do not have time to attach part 2 at the moment.

[jessebanning]

As far as my welding capabilities go: I used to work for a company called Barrier Systems INC www.barriersystemsinc.com, and was a welder/fabricator. We built highway safety products and machines and were certified through the state of California for doing work for CalTrans. All of our welds and equipment was inspected by CalTrans and numerous other government agencies we did work for.

[cbrew]

I just sent Chris a few photos to post for me.

FYI
AS of right now, I have not received any emails yet

[jessebanning]

just resent them to the correct email address

[cbrew]

so far i have 19 emails
it will take a few to process them, i will post as soon as possible
Chris

[gwrdriver]

2.6 gallons of water in a 1" scale boiler on a major rupture would expand to 600 cubic feet of steam instantaneously.

Are you absolutely certain this would be the outcome? I think "doing the math" would prove differently.

pieces of shrapnel.

When was the last time we had a live steam (as in model) accident that involved shrapnel? When? I await your anwer . . . . take your time . . . I have all day. OK I'm tired of waiting so I'll answer for you . . . NEVER . . . Let me repeat . . . NEVER. So why does someone always insist upon inserting hysterical hyperbolic terms like bomb and shrapnel into boiler discussions. It doesn't prove anything, it doesn't change the mind of someone who was looking to cut safety corners as a cheap and quick way to build a boiler. Even the most extreme destructive tests on miniature pressure vessels did not produce disintegration (ie, shrapnel.) All such language may do is alarm someone (like an inspector or codes official) who accidentally comes across such a statement and who before that moment thought those little trains were safe and the people who run them knew what they were doing. There are any number of people who go around doing nothing but looking for something to be hysterical about, but it shouldn't be one of us.

[tsph6500]

I am absolutely focused at all times of keeping the crown sheet covered.

This why there are many incidents of people running into the rear of stopped trains, splitting switches, etc.

Crownsheets deserve our attention but not to the point that YOU become a hazard to those around you.

[jessebanning]

Does anybody know anything about the copyright infringement laws? There is a concern about posting some pictures of drawings from Allen Models and Kozo. If it is an issue, I can email the photos to whomever wants them. I do not want anybody to get in trouble