Boilers

[Dick_Morris]

I'm starting a new thread as we have moved beyond the discussion of CB&Q's locomotive.

No locomotive manufacturer that built curved fire boxes built them without crown sheet stays.

That's not a good comparison. Scaling a prototype to design a 1/8 scale boiler doesn't work. The ratio of linear measurements to scale and stresses to scale don't follow the same relationship. On top of that, our boiler plates are about twice as thick as if they were directly scaled from the prototype.

In my earlier post I didn't use the right term for the girder stays and have gone back and made the correction. In the typical model boiler girder stays support the crown sheet. The firebox is supported by the mud ring, fire door ring, and back, throat, and side sheet stays. If radial stays are used they also support the crown sheet and firebox.

[jessebanning]

The CP173 boiler has plenty of clearance around the firebox. The back section of the boiler is "7.500 od and the front boiler barrel is "6.00. That is why it looks like there isn't any room. Second, the gibbs/girders, what ever you want to call them are spaced apart to allow the throttle body and plumbing clearance. It would take an enormous amount of energy to fail the .250" crown sheet. This boiler cannot generate that amount of energy. Gene Allen's 2-8-0 boiler has no crown stays, just the girders with cut outs in the to allow water circulation. Prototype locomotive boilers were made from .375" - .500" material. The surface area and volume of water and grate area are hell of alot bigger than in our model boilers. The prototypes also ran on 300psi.

[Marty_Knox]

Boiler design is a fascinating subject - I have been studying it for the last 35 years and am still learning. As for girder stays, they act as stiffeners for the crown sheet but increase the side load on the stays and the total load on the mudring. When you talk about 1/4' plate being strong enogh you must consider at what temperature? Steel loses strength once it gets above 1100 degrees F. As long as there is water in the boiler it should never reach that temperature, but what about a 'low-water event'?
I have in my scrap yard a boiler that was made from 3/16" thick steel with 3/8" stays on 4" centers. The owner wanted me to re-tube it. On close examination I found the crown sheet had all the soot burned off and had sagged down more than 1/4" about 1 1/4" behind the crown sheet. I ended up building a new boiler.
Another thing to remember is that not all steels are the same. What you want for a boiler material is not so much strength as ductility. To put it another way you want a steel that will bend rather than crack or break. The strength in a boiler comes from it's structure more than from the material.

[Marty_Knox]

Another factor to consider is corrosion. Sure, it's 1/4" thick now, but what will it be in 20-30 years? I have an ultrasonic thickness tester and have looked at a fair number of boilers built about 30 years ago. I have one in my shop now that was built in 1979. On checking the crownsheet it was .141" thick - another spot was .191". We were told it was originally 5/16' thick(.312"). The side of the firebox measure in the .220's. The shell was very close to the original thickness every spot we checked.

[Fred_V]

here is what the crown sheet stays can look like after 30 years.

[LVRR2095]

here is what the crown sheet stays can look like after 30 years.

Fred, you could sell that as "Modern Art Sculpture!" No sculptor could figure out how it was accomplished. I bet they would have a funny look on their faces when you told them it took 30 years to fashion.....
Keith

[jessebanning]

I spoke with Dan Markoff (owner of the Eureka) over the weekend about boilers. His boiler is the original boiler from the factory in 1875 made from .375" material. The only thing that needed replacement was the front tube sheet. He has the boiler inspected annually and it pases every time. He chuckled when we told him our boiler for the CP173 was made from .250". He thought it would be made out of sheet metal. Granted over 20-30 years, things start deteriorating, if not managed correctly. These are not toys that we are building and operating. They are steam locomotives. The same care has to be taken with the miniature locomotives as with the full size. There is an 1 1/2" scale heavy pacific in our club that has a 12" steel boiler and has been in operation for 20 years with no boiler problems.

[Harlock]

Is Dan's boiler a lap seam boiler? (I think that's what they call it)

[Fender]

here is what the crown sheet stays can look like after 30 years.

Can't argue with the photo, but stays should be in tension. How did they get squashed into pretzels?

[Bill Shields]

I am from the same school as Marty - only about 5 years longer (had to repeat a few grades)....

That doesn't mean I know any more (doubtful), but have had plenty of time to know that anyone that 'skimps' on a few radial stays to make building a boiler 'easier' is what Ben Franklin used to call 'penny wise and pound foolinsh'

What does it cost in terms of time and material to put the proper number of stays into a boiler, no matter what the firebox configuration, to properly carry the load expected, unexpected and future as a result of corrosion?

$50 worth of material and welding time NOW can save you a $1000's in the future if you don't have to rip a boiler off and replace it prematurely - unless of course you are just building the boiler for someone else and don't care - or are providing a design for someone else's boiler that you are never going to have to maintain.



When I build a boiler, I put in enough stays to be sure that the resultant load on the mud ring as as low as I can make it - even if this means that I put in some stays that are not really 'necssary' to prevent wrapper crush, as is the case with some of the stays shown above that are welded to the bends in the inner wrapper.

What it is - $20 worth of material? Phooey - I spent more than that on 2 cans of paint.

There is nothing magic about boiler design for our little models. You build them strong from the correct materials, provide plenty of space for water circulation, plenty of stays and lots of cleanouts so that you can take care of the boiler once it is attached to the loco.

How complicated is that? Heck, even I can do it.

PS: the only girder stay design that I personally thought was worth a hoot was one that Bob Reedy did - had transverse girders that also were stays welded into the outer shell of the boiler. I personally don't think that they were easier to install than a bunch of radials (I've got one heck of an electric drill), but Bob's design was heck for strong and should last a lifetime+.

[Fred_V]

here is what the crown sheet stays can look like after 30 years.

Can't argue with the photo, but stays should be in tension. How did they get squashed into pretzels?

the stays were cut loose from the top of the tube and a punch was used to free them from the tube so the firebox would drop out.

[Fred_V]

I am from the same school as Marty - only about 5 years longer (had to repeat a few grades)....

That doesn't mean I know any more (doubtful), but have had plenty of time to know that anyone that 'skimps' on a few radial stays to make building a boiler 'easier' is what Ben Franklin used to call 'penny wise and pound foolinsh'

What does it cost in terms of time and material to put the proper number of stays into a boiler, no matter what the firebox configuration, to properly carry the load expected, unexpected and future as a result of corrosion?

$50 worth of material and welding time NOW can save you a $1000's in the future if you don't have to rip a boiler off and replace it prematurely - unless of course you are just building the boiler for someone else and don't care - or are providing a design for someone else's boiler that you are never going to have to maintain.



When I build a boiler, I put in enough stays to be sure that the resultant load on the mud ring as as low as I can make it - even if this means that I put in some stays that are not really 'necssary' to prevent wrapper crush, as is the case with some of the stays shown above that are welded to the bends in the inner wrapper.

What it is - $20 worth of material? Phooey - I spent more than that on 2 cans of paint.

There is nothing magic about boiler design for our little models. You build them strong from the correct materials, provide plenty of space for water circulation, plenty of stays and lots of cleanouts so that you can take care of the boiler once it is attached to the loco.

How complicated is that? Heck, even I can do it.

PS: the only girder stay design that I personally thought was worth a hoot was one that Bob Reedy did - had transverse girders that also were stays welded into the outer shell of the boiler. I personally don't think that they were easier to install than a bunch of radials (I've got one heck of an electric drill), but Bob's design was heck for strong and should last a lifetime+.

me too.
plenty of stays and lots of beveled edges.