Can't sleep: dry pipes?

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Greg_Lewis
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Can't sleep: dry pipes?

Post by Greg_Lewis » Sat Jan 25, 2003 4:13 pm

I woke up this morning at 4:30 and couldn't go back to sleep, so I started thinking about my favorite subject, and somehow my thoughts wandered into boilers and then to dry pipes. Strange things happen at 4:30 a.m. I was thinking that one of my friends used stainless steel for his dry pipe, as did I upon his recommendation. Another friend uses brass; someone else warns not to use brass because the heat will draw the zinc from the alloy and lead to failure. And several of the locomotive boiler designs I've seen, including the one I used, allow for the removal of the dry pipe through a hole in the front tube sheet.

All of this to avoid trouble from a steel dry pipe rotting out over time.

But why? If you decided to use brass, can there really be a problem losing zinc and thus having the pipe fail at about 350 degrees (running 125 psi)? That ain't really that hot. Has anyone ever heard of a steel dry pipe corroding away? Wouldn't other parts of the boiler eat out faster, such as areas in the water legs or around the crown sheet and stays? Have any of you builders used common black pipe for dry pipes?

And to restate the main question: has anyone ever heard of a dry pipe failing before other parts of the boiler?

With your help, perhaps I'll be able to go back to sleep next time.

I need a nap.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 30 years of turning perfectly good metal into bits of useless scrap.

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UnkaJesse
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Re: Can't sleep: dry pipes?

Post by UnkaJesse » Sat Jan 25, 2003 9:08 pm

Greg, The Southern 4501 Mike had a dry pipe to crack before an excursion and a diesel pulled the train to a bunch of disappointed railfans. But that was in real life, I don't know about model dry pipes.

Unka Jesse
"The same hammer that breaks the glass, forges the steel" Russian proverb

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triplexJames
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Re: Can't sleep: dry pipes?

Post by triplexJames » Sun Jan 26, 2003 12:29 am

Greg
If a brass dry pipe will lose zinc from the heat then how about the water glass or safety valve. I would make it from black iron pipe. It would have the same expansion rate as the boiler. Any thing above the water line wont rust to bad. It wont rust out as long as you take care of your boiler. I would make it easy to remove.

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Trainman
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Re: Can't sleep: dry pipes?

Post by Trainman » Sun Jan 26, 2003 12:59 pm

Hi there:

saw your post about the rotten dry pipe and felt I needed to respond. I am an engineer at Tiny Town here in the suburbs of Denver and one of our steamers had this problem. I suspect that the material used in the dry pipe was not black iron. I know for a fact that it was not schedule 80 pipe. Our locomotove is used every weekend from May thru October. We have been using wate treatment in the water and that has really helped keep the inside of the boiler clean. The dry pipe when it was removed had a lot of scale built up inside it and was paper thin. As best as we can tell the shell of the boiler is about 50 years old. The boiler has had annual inspections and was reflued about three years ago.

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FredR
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Re: Can't sleep: dry pipes?

Post by FredR » Sun Jan 26, 2003 7:30 pm

You know, when I first seen the post, I thought he was getting ready to aire some personal information that I didn't think I was going to want to read. Glad now I read it :-)
But you know, I never thought anything about brass deteriorating. What about water pumps and such? Does this affect them as well? Could thins cause S.S. valves to dig into the brass valve seats? I just wonder because my expensive 20yr old duplex pump has does just this. Valves have now 'gouged' out the valve seat and a new block has to be machined.

Fred

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Dave_Haggland
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Re: Can't sleep: dry pipes?

Post by Dave_Haggland » Sun Jan 26, 2003 10:29 pm

Why not just use copper tubing? Same stuff lots of us have for flues, seems to hold up better than steel without the zinc depletion problems. DH

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Dick_Morris
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Re: Can't sleep: dry pipes?

Post by Dick_Morris » Sun Jan 26, 2003 11:13 pm

I have a piece of black iron pipe and a black iron ell for the dry pipe in my steel CP-173 boiler and I don't expect to have any problems. One thing to remember is that a leak in a dry pipe only becomes a serious safety problem when you are using a dome throttle. With the dome throttle closed, the differential between the inside of the dry pipe and boiler pressure is the full pressure in the boiler with no way to shut the flow of steam to the cylinders. With a front end throttle, the differential is zip. With a front end throttle, the worst case is you may get some water in the steam to the cylinders.

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philinmt
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Re: Can't sleep: dry pipes?

Post by philinmt » Sun Jan 26, 2003 11:42 pm

Why not use cast iron like the real thing, The one in my H K Porter is 107 years old and in the same shape when it was made..Phil in Mt

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Trainman
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Re: Can't sleep: dry pipes?

Post by Trainman » Mon Jan 27, 2003 10:35 pm

Could the reason that the dry pipe is going bad do the the fact that the dry pipe sees the steam moving through thus causing wear, where the steam in the boiler is fairly stationary and does not have the higher velocity movement? just a suggestion.

Al_Messer
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Re: Can't sleep: dry pipes?

Post by Al_Messer » Mon Jan 27, 2003 10:49 pm

That engine is probably older than both of us and was worked hard during its lifetime. Doesn't surprise me a dry pipe would fail---Murphy's Law, you know!! Seems like the cinder screen in the smoke box stopped up while it was on excursion in Nashville once and they had to pull the front access door of the smoke box open and blow it out 'cause they couldn't make enough steam.
Al Messer

"One nation, under God"

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Rolly
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Re: Can't sleep: dry pipes?

Post by Rolly » Tue Jan 28, 2003 6:13 am

Normally a dry pipe has so many holes its hard to conceive wire drawing would do any damage. I personally thing black iron pipe would last the life of the boiler. I am building a new boiler and intend to use S.S. as I have it in the shop. One reason for this is the little use over the winter months. Depending on how you lay up the boiler the dry pipe could rust at the holes and carry it into the steam line at the first use. How do most of you lay up your steel boilers for the winter? I blow mine down hot and leave it open for a few days then back fill with nitrogen.
Rolly

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highiron999
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Re: Can't sleep: dry pipes?

Post by highiron999 » Tue Jan 28, 2003 7:38 pm

I have seen a Harper Mogul with steam dome throttle lose the dry pipe to rust. I do not believe that the idea of brass losing zinc to be a real world problem, but only theoretically applicable. When is the last time a brass valve failed? Have YOU ever actually seen, or even heard , of that happening (Marty Knox NOT included in what you've heard)? Why attempt to avoid something that is so unlikely to happen? Why build a S S boiler, with the inherent risk and cost of S S? S S work hardens and loses elasticity becoming brittle, unless you pick EXACTLY the right stock, and REALLY know what you are doing when welding. Otherwise VERY dangerous, according to ASME. We, live steamers, have always used standard materials that are extra thick, for that margin of safety that has allowed us to build boilers in our basement with a phenominal safety record. Why reinvent the wheel? LBS8000 water treatment, when used as directed, is the end of rusted out boilers AND rotted out dry pipes. John Noble has a boiler at Riverside Live Steamers, over 20 years old that inside looks new. He blows down, removes the steam dome, and lets it dry thoroughly, AND uses water treatment. A light bulb in the firebox during storage with the boiler open (blowdowns, valves, etc.) will keep her dry. Marty Knox described drying out after running in his recent article in Live Steam. Dry boilers do NOT rust! So, no exotic materials OR building techniques are required for your dry pipe. Just regular steel, decent welding ability, water treatment, and keep you boiler dry when not in use, It should last indefinitely. You don't need to hide in an M-1 A-1 Tank when they are only throwing BB's at you. Leonard Evans

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