# Steel boiler question



## Amber (Jul 29, 2011)

I have a question of curiousity. If a person wanted to build a boiler from steel, would schedule 40 steel pipe be good enough for reasonable pressure? I've seen a few things on the internet where people talk about their steel boiler with copper flue tubes, so I was wondering what they use for the boiler barrel. One of the boilers that I saw had steel tube sheets welded into the boiler barrel, with copper flues. Small diameter boilers are easy enough with heavy wall copper pipe, but after a certain size, that gets difficult.


----------



## Dwight Ennis (Jan 2, 2008)

Many use steel boilers in larger scales - 1" and 1-1/2" scale. But they do rust, and because of that I wouldn't personally use steel in anything smaller. Just mho.


----------



## BigRedOne (Dec 13, 2012)

I think steel schedule 40 pipe is good for over 1,000 PSI at several hundred degrees. The pressure rating drops as the diameter increases. 

Why not use stainless? In the context a making live steam models, I'd rather pay more and not have to worry about rebuilding it.


----------



## Semper Vaporo (Jan 2, 2008)

Posted By BigRedOne on 13 Dec 2013 04:43 PM 
I think steel schedule 40 pipe is good for over 1,000 PSI at several hundred degrees. The pressure rating drops as the diameter increases. 

Why not use stainless? In the context a making live steam models, I'd rather pay more and not have to worry about rebuilding it. 

Stainless has many good properties, but not in boiler making. In the ride-on scales it is banned in the UK and OZ. Hydrogen Embrittlement, pinholing and cracking are all problems with stainless in use with boilers. It is also (contrary to common wisdom!) a very poor heat conductor. 
Use Copper.


----------



## Michael Glavin (Jan 2, 2009)

Amber, 

We use schedule 40 steel pipe @ 150 psi for laundry and dry cleaning plant construction, never had an issue to date, its pretty much industry standard for us... That said I'm building a large industrial plant presently, were using 6" SEAMLESS schedule 40 pipe together with welded fittings. All the boilers we sale and use are built with carbon steel tube sets and pressure vessels. 

Michael


----------



## HMeinhold (Jan 2, 2008)

Posted By Semper Vaporo on 13 Dec 2013 06:18 PM 
Posted By BigRedOne on 13 Dec 2013 04:43 PM 
I think steel schedule 40 pipe is good for over 1,000 PSI at several hundred degrees. The pressure rating drops as the diameter increases. 

Why not use stainless? In the context a making live steam models, I'd rather pay more and not have to worry about rebuilding it. 

Stainless has many good properties, but not in boiler making. In the ride-on scales it is banned in the UK and OZ. Hydrogen Embrittlement, pinholing and cracking are all problems with stainless in use with boilers. It is also (contrary to common wisdom!) a very poor heat conductor. 
Use Copper. 

There is a new stainless steel composition which seems to be ideal for boilers. I think I saw a discussion about this in ME. If I find it, I'll post it here.
Regards


----------



## s-4 (Jan 2, 2008)

So did they roll the copper tube ends in place? 
I'm interested to hear if you find more info on this, I like the idea of boiler welding rather than soldering of course.


----------



## Amber (Jul 29, 2011)

S-4, yes, the discussion I was looking at was about rolling the copper tube flues into the steel tube sheet. There was a picture of the front end of the boiler with the tube sheet, the weld for the tube sheet was very nicely done. I have neither the skills or the tools to do that kind of work, but I do enjoy seeing it.  
I have a piece of 10 inch schedule 40 steel tube that I ended up with that I was curious about. It's about 2-1/2 feet long and I have a hard time moving it. I got it from a local well drilling company, I was going to use it for part of a rocket stove mass heater but it turned out to be not practical to build that. I've often wondered about it's use for a boiler.


----------



## Slipped Eccentric (Jan 2, 2008)

Are you talking about duplex steel? There was a discussion about it on the Chaski board as well as a write up in Live Steam.


----------



## s-4 (Jan 2, 2008)

I've seen this done as well. It seems the copper needs to be annealed on each end first to enable the rolling process. Personally, I worry about the integrity of the copper in the annealed sections over time and cycling. Do you think the steel will outweigh the copper enough that it might affect performance on that issue alone?


----------



## HMeinhold (Jan 2, 2008)

Posted By Slipped Eccentric on 13 Dec 2013 10:23 PM 
Are you talking about duplex steel? There was a discussion about it on the Chaski board as well as a write up in Live Steam. 
I think that was it.


----------



## Slipped Eccentric (Jan 2, 2008)

Posted By HMeinhold on 13 Dec 2013 11:13 PM 
Posted By Slipped Eccentric on 13 Dec 2013 10:23 PM 
Are you talking about duplex steel? There was a discussion about it on the Chaski board as well as a write up in Live Steam. 
I think that was it. 


If so, it's an intriguing potential. The biggest downside so far seem to be that it needs a trained welder familiar with the material.


S-4, I don't think you need anneal the tubes when rolling them in. As for integrity of the joint, there are steel boilers with copper flues decades old out there. The last boiler that I saw that needed replacement developed a hole in the top of the steel firebox with the flues holding up just fine.


----------



## Amber (Jul 29, 2011)

I really don't know much about the type of steel used in boilers, I don't remember reading anything about that detail. I can remember reading about copper flues in small steel boilers years ago, but I couldn't tell you where I read it now. 
I'm not sure what kind of steel the schedule 40 pipe is made of, but I assume that if it's pressure rated for hot water or steam that it must be good stuff. The piece I have seems to be galvanized or coated with something similar.


----------



## xo18thfa (Jan 2, 2008)

General rule I've heard, anything under 6" dia is better done in copper. Over 6", steel. There are lots of boilers out there from welded steel and rolled copper flues. Go to any 7.5" gauge steam up and you'll find plenty of examples.

Welding it is the key. MIG (wire feed) is not a good choice. The flux core, 110V wire feed welders from Home Depot or Lowes will not work at all (the weld is way too porous). Look at a AC/DC stick welder. 7018 rod on DC setting.


----------



## Amber (Jul 29, 2011)

If I were to decide to use the piece of pipe for a boiler, I would have to have it welded by someone who knows what they're doing and has the proper equipment. I can solder and braize, but I don't know how to weld. 
For a 10 inch boiler, I have to wonder what size the flues should be, perhaps 3/4s inch? It's not that hard to find type M rigid copper pipe in 3/4s inch. 
My imagination can see a nice geared engine with a 10 inch boiler. My pocketbook just laughs at me...


----------



## xo18thfa (Jan 2, 2008)

The flue size is a function of length. Most of them are 1/2 (nominal) copper, which has a real diameter of 5/8". The flues on my loco boiler are about 24" long and they are 1/2". Its propane fired and steams like crazy. 100PSI all day long.

Get with your welder first thing. Plates and barrels for steel have to be beveled. The welder can tell you what to do and you can knock a lot of that work out yourself.


----------



## Amber (Jul 29, 2011)

Good idea! I would imagine that the tube plates should be at least as thick as the boiler barrel. Drilling the holes shouldn't be to big of a problem with my drill press, doing both at the same time. If I were to do it, I'd probably want to get a couple of new drill bits for that. Getting someone to cut the round tube plates and have them actually be round would probably be a lot better idea than me attempting to cut them out. It would be tempting to make a short fat vertical boiler, a dry firebox would be easier to build that way.


----------



## xo18thfa (Jan 2, 2008)

You'll need to tap holes in the barrel for fittings. Water gauge, safety all that. The barrel is thick enough to tap directly. Most are 1/4" Pipe. You can do those yourself if you have a real steady hand. Otherwise a machine shop can do it with a big vertical mill.


----------



## Totalwrecker (Feb 26, 2009)

Amber to go with your new drill bits get some drilling/ cutting oil. It's a high sulfer content oil and helps you cut true. 

John


----------



## Amber (Jul 29, 2011)

I do have cutting oil from a different project, I find it quite useful for tapping holes and drilling larger holes. 
1/4 inch pipe tap holes for the fittings shouldn't be a problem for me. It's the projects that involve machine tools like a lathe or milling machine that I can't do. The only thing I have is bench top drill press. 
I have to wonder if a 10 inch boiler would be too big for even 1-1/2 inch scale, perhaps a smaller diameter boiler would make more sense.


----------



## xo18thfa (Jan 2, 2008)

Not much machine work on boilers themselves. Lot of sawing and grinding. 

Too much steam is never a bad thing.


----------



## Dwight Ennis (Jan 2, 2008)

Drilling the holes shouldn't be to big of a problem with my drill press, doing both at the same time. If I were to do it, I'd probably want to get a couple of new drill bits for that.These are generally finished off with a reamer. Drill bits tend to make triangular holes which will cause you problems when trying to roll in the copper flues.


----------



## BigRedOne (Dec 13, 2012)

Can anyone explain the phrase "roll in?" 

Thanks, 
Matthew


----------



## Semper Vaporo (Jan 2, 2008)

"Roll in"... the flue tube needs to be sealed to the front and rear tube sheets so that no water leaks out of the boiler at those points.

The round flue is put through a hole in the front and rear tube sheet that is just barely bigger than the flue pipe outside diameter. A special tool is then inserted into the pipe that expands the pipe to fill the hole. The tool is often a small rod with three rollers (often tapered) equidistant around the rod and they roll inside the pipe, but are pushed into the pipe such that the pipe expands as the rollers go round and round inside the pipe.

This is why the hole in the tube sheet needs to be VERY ROUND so there are no uneven gaps in the fit of the expanded pipe.


----------



## HMeinhold (Jan 2, 2008)

Bill Harris uses rubber disks from a plumbing supply and squeezes (expands) them with a threaded rod. Thus the holes don't have to be perfectly round. It seems to work very well, as we own his original Shay and there are no leaky tubes after many years of operation







! The gadget is also much easier to make compared to a tube roller.

Regards


----------



## Amber (Jul 29, 2011)

The rubber disk tube expander sounds like a good idea, easier than trying to figure out how to make a tube roller. 
As for reaming the holes in the tube sheets, chucking reamers are available on ebay, just have to find the right size for the copper tube that you're using for the flues. 
I wonder how hard it would be to make a dry firebox for a horizontal boiler, I wouldn't want to attempt to do all the stay bolts for a water jacket firebox. I suppose that if you fire it with propane or oil, it would be easier than using a solid fuel like coal or wood.


----------



## NeilK (Jun 17, 2013)

Amber: 
There are quite a few horizontal boilers with dry fireboxes out there - most are referred to as "Briggs-type" boilers. It's quite popular in Australia and other locations. The big drawback is the loss of substantial heated surfaces around the firebox - it could reduce the boiler efficiency by 30-40%. In the model sizes, most of the time the loss is unnoticed as train lengths are short and run times are only a few hours. And, the backhead and firebox sides are quite a bit hotter from the lack of the water space around the firebox. The build time would be shorter though. 

Your loco - your call...plenty of examples both ways. 

Neil


----------

