Boilers

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jessebanning
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Post by jessebanning »

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.
BryceGTX
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Post by BryceGTX »

jessebanning wrote: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.
I am not looking at the function of the girder, because it appears it is not needed. It would be useful if it was stayed as they are in full size boilers.
I am not saying it is a stupid idea putting stays on the crown sheet, just not neccessary in this application.
I understand the argument. The problem comes if a noob creates a boiler very similar to yours and it is not well done. Suppose, he used no leg stays and no crown support. It could be the boiler will work fine.

Our answer to him is to use proven design techniques. Fully stayed legs and crown sheets. You can then use the simple stay calculations to verify the boiler design.

I prefer to say nothing of LE or Allen boilers without seeing pictures.

The biggest reason I bring up this discussion is that I will design and build my own boiler. My boiler design will be verified through calculations and use good construction techniques.
Bryce
jessebanning
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Post by jessebanning »

I'll have to email some pictures to you. My laptop sucks and I cannot resize pictures to fit this forum. :cry:
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Dick_Morris
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Post by Dick_Morris »

Does anyone have an example of the calculations and design notes done for an 1-1/2" scale boiler that they would be willing to post? It would probably be very informative. (There is also the chance that someone will start throwing rocks. :( )
jessebanning
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Post by jessebanning »

I have a few drawings for 1.5" scale boilers. I can email them to someone if they can post them. My laptop isn't the greatest and I don't think I can do it from my iPhone.
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cbrew
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Post by cbrew »

Hey Jesse,,, send them my way
Chris
If it is not live steam. its not worth it.
jessebanning
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Post by jessebanning »

Will do buddy. I'll send em tomorrow morning when I get to my shop. Thanks Chris.
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cbrew
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Post by cbrew »

No problem! :wink:
If it is not live steam. its not worth it.
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Bill Shields
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in General

Post by Bill Shields »

The example firebox with the stays above the 'bent' sections of the firebox are a perfect example of girders that really do very little to strengthen the firebox. They would be better placed over 'flatter' areas.

Are Allen and other similar boilers unsafe?

Try to get a National Board inspector to approve one and see what he has to say about the designs. Vapor lock would be the result in some of the cases / examples I have seen.

What many of you also fail to take into account is strength of welds. You are all 'assuming' that everything is 'perfect'. How many boilers are welded by qualified welders?

Add up the lot of

1> improper materials
2> not-up-to-snuff welds
3> questionable designs
4> corrosion
5> lack of heat transfer (localized overheating) because of scale buildup or bad design that won't allow for proper circulation.
6> occasional dry crown sheets caused by low water / severe downhill grades
7> Accidental DERAIL and roll over on side (it DOES happen). You don't want your boiler to catastrophically fail because it is on it's side and HOT, in the time it takes you to rake the coal fire out (unless you run propane or oil, you should consider this).
8> other things that I cannot think of right off the cuff but others may wish to add

When will all of the 'worst situations' add up and cause something fail because a bad boiler? How much does it cost to build a boiler that is REALLY safe under all circumstances.

Calculations of boiler stay loads is very complex, expecially when you have to also consider expansion / contraction of firebox relative to outer wrapper - which is one of the reasons why they had flexible stays in certain areas to overcome the problem of bending.

As I said before - the whole lot of you that think you are saving a few $$ on boiler construction by not putting in the proper number is stays are being very risky and foolish...like comparing a home pressure cooker to a loco boiler.

Has any of you that are 'cutting corners' (in any way) ever done the calculations on how much energy is explosively released when 3 gallons of 100 PSI water flashes into steam because of a sudden pressure release such as can be caused by a weld letting go or a crown sheet cracking?

It's enough to get you running for kevlar underware and wishing you were someplace else at the speed of sound....

Sometimes, when I see what people are doing (or aren't as the case may be), I think that required state inspection of boilers isn't such a bad idea (just briefly)....

Want to play the calculation game, OK, let's lead off and see where this goes. I will tell you all that I have $700 worth of PVQ material and some bending costs in my boiler, and I didn't shop around at all. Had I opted for fewer stays / girders, I might have saved $30 total on materials (whoopee) - the price if a couple of buckets of KFC chicken. Better to put the $$ into the boiler and NOT eat the chicken.

Let's simplify and follow through some calculations.

Rule #1: I never use the mud ring as a vertical load support member in calculations. Calculations of the load on those welds is quite complicated, so I get around that by assuming = 0. If I assume nothing, I can lose nothing. Anything that I then get is 'safety factor' and not needed for normal load.

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.

Using THIS number for maximum firebox motion from vertical pressure, I can then calculate the WORST CASE load on the non-vertical stays (no temperature considerations). This lets me calculate load on non-vertical stays as a combination of direct tension and shear.

Notice that for the vertical stays, I am not calculating load based on spacing of the stays, because the TOTAL load is much higher than that because of the firebox shape.

For side stays, load IS a function of spacing since the area of the plate IS the load area, not the open area of the firebox as above.

Next: Anyone want to calculate the shear load on the welds of these 32 stays?

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.

After we get done all this, we NEXT calculate what happens to things if / when the firebox goes dry and is exposed to combustion temps (think accidental roll-over).

After all, it CAN happen and wouldn't you all like to know that your boiler CAN survive it?
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makinsmoke
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Boilers

Post by makinsmoke »

Somewhere in the vast accumulation of stuff I call reference material I can't put a hand on is a copy of Mainline Modeler wherein is a description and photos of a propane tank car at Kingman, Arizona that fails.

Granted, there are worlds of difference between propane tank cars and steam locomotive boilers, but there are certain physical characteristics that are germain.

In the case of the propane tank car. One of the fittings failed on the top of the car, releasing propane which ignited. While burning, the propane contributed to the metallurgical failure of the tank shell, thereby releasing to atmospheric pressure the balance of the propane contained in liquid form under pressure. The resulting BLEVE as described enveloped an area roughly 1/4 mile in area and killed several people.

The liquid versus gaseous properties apply to steam locomotives as well as tank cars, and I think that is what several folks that are forwarding concerns here are coming from.

Once a container fails that holds liquid (water) under pressure and temperature, that liquid then reverts to atmospheric pressure releasing the enery as it changes from liquid to vapor.

As Joseph Foster Nelson wrote a lot of years ago, for a 1" K-4s boiler, 2.6 gallons of water in a 1" scale boiler on a major rupture would expand to 600 cubic feet of steam instantaneously. Do the math. That is a lot of area. Not including the flying pieces of shrapnel.

Guys, we can agree and disagree on alot of things, but safety and physics are critical to our hobby for it to survive.

I am not afraid of running a steam locomotive but having the above information in my head I am absolutely focused at all times of keeping the crown sheet covered.

My two cents.

Brian
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tsph6500
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Re: in General

Post by tsph6500 »

Bill Shields wrote:we NEXT calculate what happens to things if / when the firebox goes dry and is exposed to combustion temps (think accidental roll-over).
I can answer this one....

Water below the bottom nut? Close the throttle, use no blower. Boilers don't fail the instant the crownsheet is exposed. Remedy the feedwater problem. Unable to do so within a reasonable amount of time? Drop the fire. It's close to being out anyway.

Rollover? Your fire is all knocked to hell when the grates fall onto the crownsheet or side sheet. There is no longer a 1400˚F fire heating your now submerged crownsheet (if your drivers are pointed skyward) even if the throttle is wide open. There's no draft through the fire, it goes out.

Dust yourself off, close the throttle and look for your hat.

This is not a theory, I've seen it several times, highlines and ground lines.
Best regards,
Jim Leggett

Montreal Live Steamers
www.montreallivesteamers.org

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bcody
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ROLLOVER

Post by bcody »

Jim: I just close the fuel valve and then correct any water problems.


Bill
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