Deanofid said:
Is there any reason not to use C101 tubing for a boiler? Reason I ask is, the place I'm looking at, (Online Metals) has a much larger selection of tubing in C101 than in C122.
Zee,
I guess I'm showing my age but back before the emergence of on-line metals sources, when I went to my local pipe & supply to beg a crust of copper tube, I would generally only find tube in C122 and plate in C110. C101 would have to be ordered and therefore would be more costly, typically because I'd be required to buy a full length, and it would take longer to get. I'm not a metalurgist but so far as I know those are the only reasons C101 isn't used interchangeably with C110 for model boiler work. Now that on-line sources are the order of the day I don't suppose the foregoing is of any consequence any more. TEL is correct that C101 is the alloy used for electrical components and I also think it is required for some manufactured items and welded copper applications.
So basically, is C101 okay for a boiler?
My answer has to be, assuming there is no appreciable difference in cost or availability, I don't know of any reason why it wouldn't be.
For small models, what would be typical OD? or ID?
OD, because we will mostly be offered tube and as you have (or soon will) discovered US standard copper plumbing tube is 1/8" over nominal OD size. This puts some of us (those who build to locos to British designs) at a disadvantage because most British designs call for actual dimension OD tube and historically copper tube in increments of 1/8" could be had in the UK. As for typical sizes, that would depend . . . US Gauge 1 live steamers typically use 2" tube but beyond that I can't say there is a typical size as everything is dependant and varies upon scale, gauge, and prototype.
What about a boiler? Say big enough for a 3.5" loco.
I'm not sure what you are after here, so I'm going to throw out what comes to mind - tube gauge or thickeness. There are a number of formulae from several respected sources (Greenly, Harris, Evans, Hiraoka) which set out the mechanical design guidelines for model boilers, one of which is the thickness or gauge of the shell/barrel for a given diameter. A phenomenon of copper boiler shell design is that as boiler OD increases for a given working pressure, so must wall thickness increase in order to retain a given safety factor.
For instance, if you had a boiler with a 3" nominal OD shell to be run at 100psi, the minimum wall thickness (according to the formulae) might need to be say .080" (my quick guess.) But if the shell OD was increased to 4", all else being the same including working pressure, the .080" wall would be insuficient to retain the same factor of safety and would need to be increased, say to .095". Also, the practical pressure limit for copper model boilers of any size or wall thickness has been found to be about 125psi. Above that pressure the temperature of steam begins to reduce the tensile strength of copper to a point where it can no longer retain the required factor of safety.
In the US copper tube will be supplied in one of four wall thicknesses, Type K, L, M, and DWV. You can see the differences in the Copper.Org web pages. Very generally speaking, Type DWV is too thin-walled to be safe for any live steam application and should never be considered. Type K on the other hand is always overly heavy for boiler work thus its much higher cost is not repaid in increased performance or greater safety. That leaves Types L and M. I personally always use Type L as it not only always exceeds the required formulaic thickeness per diameter but it gives me a good stiff structural base to attached bushings and other things to. Type M on the other hand runs a little thin with respect to the formulae although it is usually sufficiently thick to meet the pressure and safety requirement for a given size. In small boilers Type M walls can be a bit thin and will tend to flex or dent more easily than Type L. That's not a deal-killer but if I send a boiler to someone I don't want to get a phone call asking "Wot's this dent doin' in me boiler?"
Brass tubing/piping seems less expensive. What about that?
Brass is inappropriate, and dangerous, for the structural components of model boilers due to the phenomenon of dezincification. Fittings and attachments in brass while not preferred can be used because they can be removed and replaced if needed.
No. You are thginking a lot (a good thing) because there is a lot to learn, but not too hard.
