Boiler stays and heat expansion

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NP317
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Location: Northern Oregon

Re: Boiler stays and heat expansion

Post by NP317 » Tue Jan 16, 2018 11:43 am

In full-sized locomotive boilers (think logging 100-ton range), I have witnessed a green fireman bring the pressure up too fast.
Result: The water temperature near the rear mud ring was so low I could keep my hand on the outside of the firebox sheet without getting burned, with 180 psi on the gauge!
This temperature differential is what can break stays. I've heard that nasty !POP! under such circumstances. = work to do.

Solution: Do things that circulate the water during fire-up.
- Periodic opening of a rear blow down valve allows water flow to get established. The a swift closure of the valve "stirs up" the water, distributing the heat energy.
- One locomotive owner in Washington State rigged up an electric pump connecting the mud ring area blow down to the steam dome. During fire-up the water was constantly circulated until pressure began to rise. This succesfully shortened the steam up time, and prevented stay breakage.

I'm even careful when firing up my 1/8th scale locomotives, for the same reasons. Periodic opening of the blow-down valves are my solution.
Maybe too cautious, but better safe than sorry.
My two $0.01s worth.
~RN

rkcarguy
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Re: Boiler stays and heat expansion

Post by rkcarguy » Tue Jan 16, 2018 12:13 pm

That's correct, I did a google image search and it's the Briggs type boiler I had seen earlier. For my long term plans, 10" Sch 40 is very close to the scale diameter of the boiler on the 0-6-0 I want to build. My thoughts are I'd fabricate a fire box from plate and cope it into the tube, then use thin fire bricks on the bottom and sides so the exposed plates don't glow red all the time. I'd be using propane and building 2" scale, so I would have the space to do it I think.
I don't think this design would require any stays. I think I'll post a sketch soon:)

Pontiacguy1
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Re: Boiler stays and heat expansion

Post by Pontiacguy1 » Wed Jan 17, 2018 9:40 am

You will still have to use either stays or bridge girders on the crown sheet area of your briggs type boiler. Also you will need some through tubes, which also act as stays, to keep the backhead in place. The biggest advantage of a Briggs boiler is that it is a lot easier to build. The disadvantages are that it will not be as efficient or produce quite as much steam as the same size water-legged locomotive type boiler, and the water circulation is not as good. If properly sized, though, a slight loss in efficiency will probably not matter too much, and I've known several people who have built and run locomotives with Briggs type boilers very successfully for a number of years. Good luck to you.

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FLSTEAM
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Re: Boiler stays and heat expansion

Post by FLSTEAM » Wed Jan 17, 2018 9:55 am

Asme code calls out A36 to be used for stay material because it is soft and is does have give to it.

John B
http://www.ngshay.com/
Shay drawings and castings

rkcarguy
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Re: Boiler stays and heat expansion

Post by rkcarguy » Wed Jan 17, 2018 3:34 pm

FLSTEAM wrote:
Wed Jan 17, 2018 9:55 am
Asme code calls out A36 to be used for stay material because it is soft and is does have give to it.

John B
John,

Most A36 is dual spec these days and meets Grade 50 requirements, I submit dual spec certs all the time for projects. They also make pipe sized tube to the A500-grade-B standards that is gorgeous looking stuff. Most of the pressure vessel stuff the pipe shop does is A53 seamless, stainless, or 516-Grade 70 material. So I'm curious what's being used specifically?

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FLSTEAM
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Re: Boiler stays and heat expansion

Post by FLSTEAM » Wed Jan 17, 2018 4:01 pm

Section PG-13 Staybolts attachment by welding shall be with SA-36 or SA-675.
Now this is from my 1995 ASME Code and it is possible that there have been changes since then.

John B.
http://www.ngshay.com/
Shay drawings and castings

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