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Steel Boiler Tubes

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GoCreate05/02/2011 16:38:38
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Chris Gunn's article (issue4396 ME) made very interesting and informative reading. I can certainly see a retube will be easier at an earlier stage of boiler tube deterioration.

I am building a 3" Allchin, I bought a commercial steel boiler however, the design does not provide a hand hole as in Chris Gunn's case, I can see that in my case if the tubes are allowed to deteriorate the same extent then I would have some very difficult problems removing them without some access to the inside of the boiler. If a tube was to collapse I can't think what I would do.

The tubes on my 3" scale are I think 3/32" as compared to Chris Gunn's 1/8" so presumably they should be replaced at an earlier. What are the experiences of owners of 3" scale traction engines? When should I consider renewing?

Is stainless steel a viable option to mild steel? I have never heard of stainless steel being used.
Does anyone use copper tubes in their 3" scale steel boilers?
 
Cheers
Nigel
Nicholas Farr05/02/2011 21:54:48
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Hi, most stainless steel has a linier expansion 1.5 times that of mild steel per degree C. So you may find buckling of your tubes. Other than that I don't know.
 
Regards Nick.
John Olsen05/02/2011 23:48:24
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"Stainless steel" is a general description that covers a wide range of materials. Some would be suitable, some would not. Full size water tube boilers these days apparently sometimes use material that we would regard as stainless steel. But unless you really know your materials, it would be better to stick to the standard grades of steel used for boilers. The wrong grade of stainless is quite likely to be worse than normal material. Some grades are prone to chloride cracking.
 
Normal steel tubes should actually be able to last quite well, given a bit of attention to water treatment. Typically we don't actually use our boilers enough, they spend too much time in storage, which is probably where the damage occurs. They should be either bone dry, which would be best, or chock full of deoxygenated water, which is OK for shorter idle periods. The worst is of course to be partly full of water, which will cause corrossion around the water line.
 
Conside how quickly a lathe bed can pick up a film of rust over winter, then remember that the boiler typically does not even have a film of oil to protect it. So a few rapid changes of temperature will soon kick off some corrosion in a boiler.
 
regards
John
Martin Johnson 126/02/2011 16:36:32
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Don't use stainless tubes in a MS boiler shell. The stainless is more "noble" than the rest, so you will set up a galvanic cell leading to very rapid corrosion of the mild steel.
 
Best way to use copper tubes in a steel shell is to silver solder them to seal them. This stops them creeping lengthwise due to thermal expansion.
 
There is some discussion about copper tubes in a steel shell, but if famous boiler inspector John Glaze says its good - then that is good enough for me.
 
 
Cheers
Martin

Chris Gunn26/02/2011 17:49:02
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Thank you for the kind words regarding my boiler retubing article. When I was collecting information before I started on my 4" Garrett, I spoke to a gentleman who had repaired a vertical boiler for a boat, and he had the very problem you describe. It was at that point he cut a manhole. I am currently building a 6" Garrett, and have bought a commercial boiler for that, and it too has come without a manhole door, just a dummy ring welded on for a dummy door. I am not sure why the manhole doors are being omitted, it is one less hole to seal, I suppose. I intend to follow all the aftercare recomendations that came with my new boiler, I will mill a clearence in the smokebox door ring as I build it, so I can pull the tubes out, and I will replace the tubes after about 8 years. This is on the basis that they will pull out OK if they are not too bad, and I will not need a manhole.
Chris Gunn
John Olsen27/02/2011 00:35:56
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There may be some nervousness about manhole doors due to the accident that occurred in the UK with a steam launch. I don't have the full details, but my understanding is that a manhole (or possibly handhole) was leaking and an attempt was being made to get it to seal better, which lead to a disasterous release of steam, leading to fatal burns.
 
I'm told by guys who work with full size boilers that the modern materials are not as good as the older asbestos based seals.
 
It is arguable that if the only time you will need the manhole is to retube, you might be better to go without, even if it makes the retubing harder. I can see that this does lead to some difficult gynecological work, getting the remains of the old tubes out through the smokebox tubeplate. Never mind, I am building a steel water tube boiler, and had those sorts of problems getting the tubes expanded inside the lower drums, which are only five inch diameter.
 
regards
John
 
mgj27/02/2011 09:13:57
1017 forum posts
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I shall shortly be starting a 4" Little Samson. The drawing shows a manhole, and I shall certainly want the manhole operational because of that article. I can put one of those dental mirrors in and check the tubes - that was the idea.
 
With my 3" LS, I agree that initially sealing the manhole was problematic (I did it all while running on air) Once the solution was found, it sealed immediately and has been trouble free for the year that the engine has been running.
 
All I did was to use plumbers hemp and load it with Foliac Graphite, to form a fibrous matrix to hold the paste, and then did up the clamp.. No gaskets. Let it set, filled the ring with water and  checked for bubbles at 125psig off the compressor.
 

Edited By mgj on 27/02/2011 09:17:53

GoCreate27/02/2011 21:19:22
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387 forum posts
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For corrosion prevention in long term storage would it be possible to fill the boiler with an inert gas like argon to eliminate oxygen? I am sure the boiler would have to be dry on the inside first and sealed after being filled? Would it increase the life of the boiler tubes?
 
Just an idea. Crazy or what?
 
Nigel
DMB27/02/2011 23:53:53
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Re comment by `tractionengine42` about flooding interior of boiler with Argon gas. Wouldn`t this be difficult/expensive to source? How about these 2 cheap and easily obtained materials - chalk and vinegar. Could be mixed up in say a bucket and let it get on and fizz. Use a glowing strip of wood to slowly lower in to bucket and when it goes out, you know how full the bucket is with carbon dioxide. Much heavier than air so you can pour it like water into your boiler. Not tried this but think it should work OK - based on school chemistry lessons.
Nicholas Farr28/02/2011 00:12:57
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Hi John, carbon dioxide is not strictly regarded as inert. DIY argon welding gas in the small desposable cylinders is not that expesive, and a lot more convenient to use.They are fairly widely available to.
 
Regards Nick.

Edited By Nicholas Farr on 28/02/2011 00:14:08

Frank Dolman28/02/2011 02:20:42
106 forum posts

Damp carbon dioxide would promote rusting unless all the oxygen waspurged
out. Depending on the particular boiler, it might be simplest to dry it out by
blowing a stream of hot air through it.
Inert gas is all very well, but sealing would have to be very thorough if air was
to be kept out for a matter of months. It is a bit of a joke that argon is probably
cheaper than nitrogen when the cost of getting hold of a cylinder is taken into
account
KWIL28/02/2011 09:38:30
3681 forum posts
70 photos
I am given to understand that a coating of tannin helps to prevent rusting when a steel boiler is out of use. Anyone want to pour cold tea on that one?
JasonB28/02/2011 16:51:57
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Most of the boiler treatments are tannin based so that would sound right. Usual advice when not using the engine for a length of time is to completely fill the boiler with a stronger than usual dose of treatment or completely empty and put a small heater or lightbulb in the firebox to keep it dry.
 
J
GoCreate01/03/2011 01:08:40
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387 forum posts
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Maybe it's possible to run some trace heating cable through the tubes, make it nice and cosy. more expensive than a light bulb though.
 
Nigel
DMB01/03/2011 09:09:56
1585 forum posts
1 photos
Hi Nicholas,
My suggestion for using carbon dioxide was that chalk is free - its everywhere around Brighton and all you need is the cheapest bottle of vinegar that money can buy.It was one for the "tightwads" of this world!
John

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