Stainless steel boiler/exchanger?

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BClemens
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Re: Stainless steel boiler/exchanger?

Post by BClemens »

What actually happens when one of these small boilers fails? Let's say it was a 516-70 steel boiler with, let's say poor welds that cracked. A poorly welded Ø8.25" steel boiler made with schedule 20 (.250 thick) for a 1/8th sized consolidation - (not a large locomotive). It cracked at a most vulnerable area - crown. It was carrying 100 lbs of steam.... anyone seen it happen?

BC
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NP317
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Re: Stainless steel boiler/exchanger?

Post by NP317 »

Is this a recent event you are referring to? I am interested to know more.

Four years ago, we (Kitsap Live Steamers) did research on hobby boiler failures in preparation for a presentation to the Washington State Pressure Vessel Inspectors 50th Anniversary Meeting in Seattle. We could find no recorded explosions, only slower depressurizing failures. None. The closest we found was a crown sheet failure years ago, reportedly at Los Angeles Live Steamers, that caused depressurization and clouds of steam, but no explosion.
And none of the attending Inspectors knew of any Hobby Boiler explosions either.

Partly due to this fact, Washington State Dept. of Labor & Industries Pressure Vessel Division proposed changes to Laws and partially de-regulated Hobby Boilers. They no longer require annual Hobby Boiler re-certifications to be performed in front of their paid inspectors. State law has been changed to allow our Clubs to perform the annual test work and record the results, kept available for State inspection if needed. A new Hobby Boiler still requires initial State inspection and certification of design and function, with associated fees.

So if there has been a recent recorded explosion in our class of pressure vessels, I would like more information, please.
~RN
BClemens
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Re: Stainless steel boiler/exchanger?

Post by BClemens »

No, there have been no explosions that have been reported that I know of, I was interested if there had been and the results of the failure. I realize it wouldn't be anywhere near a 'larger' boiler failure with much larger capacity than these small hobby boilers. I had read that a small boiler failure is as you describe: 'a depressurization' but not rapid enough to be described as an explosion, just clouds of steam. (may need to change some drawers)

So, abiding by a set of boiler construction 'standards' such as the AMBSC has set forth, and a qualified welder, a safe 'little' boiler would result - that still cannot be made totally idiot proof.
pat1027
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Re: Stainless steel boiler/exchanger?

Post by pat1027 »

BClemens wrote: Mon May 28, 2018 6:07 am What actually happens when one of these small boilers fails? Let's say it was a 516-70 steel boiler with, let's say poor welds that cracked. A poorly welded Ø8.25" steel boiler made with schedule 20 (.250 thick) for a 1/8th sized consolidation - (not a large locomotive). It cracked at a most vulnerable area - crown. It was carrying 100 lbs of steam.... anyone seen it happen?

BC
I was on a locomotive with a 10" boiler when a fire box sheet failed due to corrosion. I looked at the stack, noticed a wisp of steam when the blower and throttle were shut. I said "Hmm, that's not a good sign". By and large I suspect most model boiler failures are not dramatic failures. Compared to their big brothers model boilers are more heavily built and more quickly removed from service when there is an issue.
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Fender
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Re: Stainless steel boiler/exchanger?

Post by Fender »

I have observed two failures, and am aware of a couple more, but in all cases the result was the inability to maintain pressure, because of steam and water leaks in the firebox. The causes were corrosion from scale buildup, tubes leaking due to overheating from low water, or in one case, deterioration of sil-fos brazing in a copper boiler.
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James Powell
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Re: Stainless steel boiler/exchanger?

Post by James Powell »

I am aware of one, in the form of a 3.5" gauge copper boiler that the side stays pulled away due to poor penetration of silver solder. By the most part, I suspect that the physics of the situation mean that the cubic roots are working in our favor, and that it is unlikely to cause a death or injury even in 7.5" gauge engines. Not that it is impossible, but that there is relatively limited ways in which boilers can fail, and those ways tend to be mitigated by the designs that are used from a catastrophic failure prospective.

I think that there has been one death ascribed to model boiler failures, in the 1920's. While there probably have been others, it is so unusual that they are almost a story spread from father to son... Even in full sized steam, I can only think of a very limited # of deaths over the last 20+ years that I have followed professionally being attributed to steam related deaths. (and about equal #'s of furnace related ones...). While there is no doubt, risk, I think that it is not all that high of one. I believe you would find more benefit to work on tie down systems for engines in vehicles than on improving boiler safety in the hobby...

James
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NP317
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Re: Stainless steel boiler/exchanger?

Post by NP317 »

Thanks all for your input.
Verify's present day thinking on the safety of our Hobby Boilers.
~RN
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Greg_Lewis
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Re: Stainless steel boiler/exchanger?

Post by Greg_Lewis »

What's interesting in every thread on this subject is that there is much discussion about boiler materials and construction but nothing about the reason for most failures: people. Clubs may be rigorous about boiler inspections but how many have any sort of qualifications for the person operating the locomotive? Anyone can buy a locomotive but where is the check to see that they know what they are doing?
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
pat1027
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Re: Stainless steel boiler/exchanger?

Post by pat1027 »

From my observation and time as a club boiler inspector, most failures are due to corrosion. There are at least a couple threads about proper care, one just recently. True anyone can buy a locomotive. But most are serious about owning and operating the locomotive and seek out the information they need. Look at this thread. 68 posts this morning and over 3500 views. There are a hand full of people participating and hundreds more following the discussion.

The discourse in threads like this have a huge value for the hobby.
BClemens
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Re: Stainless steel boiler/exchanger?

Post by BClemens »

Tough to imagine the amount of energy released to do this: VGN-800
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rkcarguy
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Re: Stainless steel boiler/exchanger?

Post by rkcarguy »

I think what plagues most boilers is the differentials in heat expansion. I'm sure the tubes get hotter, and longer, first, once the boiler is fired.
I wonder if 303 stainless might be the cure? Notice that mild steel and copper boilers have obviously been used for centuries and are reliable, these two metals are also not heat treatable and do not work harden. 303 stainless is also a free machining metal and is not heat treatable as well. It could be that the soft nature of these materials allow expansion and contraction many many times, whereas the work hardened(soldered/welded) areas of other alloys such as the firebox tube sheet to tube joints are prone to failure?
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Harold_V
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Re: Stainless steel boiler/exchanger?

Post by Harold_V »

303 would be a terrible choice, as it (generally*) contains sulfur, and is not recommended for welding. Beyond that, the history of heated stainless pressure vessels is pretty well documented. They suffer chloride corrosion, which would likely be all the worse with 303.
*Sulfur containing 303 is designated as 303S. Free machining can be accomplished by the addition of selenium instead (303Se), which actually improves machinability, at least in my experience. Both alloy types also contain traces of phosphorus, and have a high coefficient of expansion. Al in all, not a great choice for a boiler.

H
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