dolfa
Gandy Dancer
Posts: 11
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Post by dolfa on Dec 14, 2006 19:53:59 GMT -5
Is it possible to braze copper wrapper,back-head etc. to 7"
stainless steel barrel 1/8" thick?
Dolfa
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jones
Gandy Dancer
Posts: 3
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Post by jones on Dec 18, 2006 6:55:15 GMT -5
Hi Dolfa,
Don't use stainless steel for boilers. Apparently, pinhole cracks will appear and the entire boiler will have to be scrapped. (This is just what I have read, I have never actually seen a stainless steel boiler). I think that here in Australia the AMBSC has banned stainless steel for use in boilers for this reason.
Regards
Andrew
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dolfa
Gandy Dancer
Posts: 11
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Post by dolfa on Dec 18, 2006 19:29:08 GMT -5
Hi Andrew,
I was thinking about stainless steel as an alternative to copper,because it is very hard to
find a copper pipe 6.5-7'' dia. 28"long.
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Post by GoldenSpike53 on Jan 2, 2007 12:53:03 GMT -5
Yes, it is hard to find copper pipe in that size....
Also, for the scale that it sounds like you are building, few people I know will build a copper boiler. I have talked to a couple of people that have built the copper shell from sheet stock and rolled it, then riveted it together along the seam and silver-soldered that along with the rest of the connections. The seam is place along the bottom of the boiler to hide it from view. Don't know how easy/hard that would be, but I'm sure it's possible. So you don't Have to have a 6.5-7" copper pipe to make the shell, it's just easier that way....
Not sure about the stainless steel issue; most people I know who don't use copper will use steel plate and pipe welded together, with copper flues pressed or rolled into the flue sheets. Copper has a much higher heat transfer rating that steel. Stainless steel is even worse.
Good luck!
Dale Dennis
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Post by gwrdriver on Jun 11, 2007 11:54:44 GMT -5
Don't use stainless steel for boilers. Apparently, pinhole cracks will appear and the entire boiler will have to be scrapped. This is known as stress corrosion cracking and is why amatuers should NEVER use stainless steel for a boiler. As does England, and it is regularly and widely discouraged in the US although we don't have model codes or insurance regulators to satisfy so some builders in the US still build in stainless, usually for reasons of purceived cost and convenience, but also often due to misunderstanding its thermal efficiency and strength. These days, where we (in the US) live with a subastantial reduction in the number of sizes of copper tube compared to say 40 years ago, most model copper boiler design barrels are odd-ball sized, especialy those from England. Their practice over the years has been . . design the model to scale and make whatever needs to be made to fit the scale. The remedy for non-standard boiler barrel sizes has been to roll and rivet. This has been a common practice for many years. Is a solid drawn tube better . . . yes, but not because it's a stronger but because it requires less work and is more dimensionally stable base upon which to build. There is nothing at all wrong with rolling and riveting a barrel but there are recommended ways of doing it with regard to seam/joint type, seam width and lap, and rivet location and spacing. If certain minimum seam requirements aren't adhered to then of course this creates a potential weakness and this a safety problem. Also somewhere on this board I saw a reference to the model boiler "safety factor" stated as "around 6" which is not quite enough. For many years the accepted safety factor for model boilers has been EIGHT. Cheers, Harry |
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Post by Harlock on Jun 12, 2007 1:39:29 GMT -5
Chloride Stress Corrosion was also covered in this thread here: livesteam.proboards23.com/index.cgi?board=kozo&action=display&thread=1148436278&page=1Starting lower down on page 1 and continuing to page 2. Ed Hume gave a good reference to a Modeltec article about the subject, and some good materials engineering considerations. Jessebanning hasn't logged on Since Feb, so we don't know what became of the stainless steel boiler that he supposedly built despite strong encouragement not to.  --M |
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Post by anil1952 on Mar 16, 2010 23:39:52 GMT -5
I want a step by step guide for assembling/brazing a boiler from a boiler kit. The sequence should be correctly described and should be accompanied with photos or a video. Any good source for this, as one has to get the boiler just right.
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Post by pkastagehand on Mar 17, 2010 15:26:51 GMT -5
I want a step by step guide for assembling/brazing a boiler from a boiler kit. The sequence should be correctly described and should be accompanied with photos or a video. Any good source for this, as one has to get the boiler just right. I don't know if any such thing exists unless it comes with the kit. Maybe someone out there has such an animal. My experience is with books that talk about or describe in varying detail the process of building a boiler from sheet stock or from a tube and sheet stock. The Kozo Hiraoka book on building the Pennsylvania A3 is a good one for a step-by-step process. His other books I am not familiar with so don't know how much of the process he describes and how much is left as assumed. Many other books give more or less ideas, plans, hints, etc. Kozo's A3 book is also a good (but not the only) source of info on the silver soldering process for boilers. Paul |
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Post by Dan Rowe on Mar 27, 2010 17:04:59 GMT -5
Also somewhere on this board I saw a reference to the model boiler "safety factor" stated as "around 6" which is not quite enough. For many years the accepted safety factor for model boilers has been EIGHT. Cheers, Harry Without stating the referenced model book or model code for further information the statement of a boiler factor of safety to be some specific number or another is not really all that helpful. In the book “Model Boilers & Boilermaking” by N.K Harris he states that the factor of safety should be between 6 and 10 and that a good all-round figure is 8. This is the number used for shell thickness calculations. In the section about staybolts he states that a minimum of 10 should be used for the factor of safety. The table 6 for staybolts follows this rule and uses about 10 for the factor of safety. Now we also have to state the maximum allowable stress for copper which is given as 25,000 pounds per square inch. The formulas do not have a factor for loss of strength at higher temperature where it is well known that copper looses strength. The Martin Evans book “Model Locomotive Boilers” also states a factor of safety between 6 and 10 and uses 8 for shell calculations and 10 for staybolts. The strength of copper is given as 25,000 psi. The difference in the formulas is there is a factor for elevated temperature to compensate for the loss of strength in copper. The real issue is to make sure that you meet or exceed the model boiler code in the location that you are constructing and operating the boiler. In the US this is regulated on a State level. Most States do not have much regulation for model boilers but a few do such as the State of Maryland. See: calslivesteam.org/calboil.htmThe Maryland model boiler copper code uses a factor of safety of 5 and the maximum allowable stress of copper is given, as the temperature and pressure go up the allowable stress is reduced. Note that none of the formulas use the factor of safety directly; the formulas use the values for the maximum allowable stress for the given conditions of temperature and pressure. The factor of safety for model carbon steel boilers is 4 and there is no reduction in the allowable stress for pressures that do not exceed 250 psi. The AMBSC is looking into the use of Duplex 2205 Stainless Steel for boiler use for more information on this see: www.pnc.com.au/~wallison/AALS/Resources/Boilers/2205.htmlDan |
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