Olfelt
- DetroiTug
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Re: Olfelt
Quote: "Why is it most VFT boiler tubes are welded in and not just expanded?"
Less probability of leaking at the rolled joint. Heard of several accounts of folks having to re-roll tubes. Our little boilers are often overfired at steamup which can cause the upper tube portion to overheat - expand then contract when cool and then leak. Roper warned about this and stressed that VFT's should only be started up full of water to prevent overheating the upper tube portions. The Stanley guys with the rolled in copper tubes are often re-rolling tubes. Of course they would be easier to replace than welded in tubes.
Fred, thanks for the short dissertation on the process and it doesn't sound too pleasant. Hydrochloric acid, solvents, having to dispose of 40 gallons of it after use, the fumes when using the cutting torch from the acids and solvents, working inside a small water leg on the bottom, nahh sounds easier to build a new one.
-Ron
Less probability of leaking at the rolled joint. Heard of several accounts of folks having to re-roll tubes. Our little boilers are often overfired at steamup which can cause the upper tube portion to overheat - expand then contract when cool and then leak. Roper warned about this and stressed that VFT's should only be started up full of water to prevent overheating the upper tube portions. The Stanley guys with the rolled in copper tubes are often re-rolling tubes. Of course they would be easier to replace than welded in tubes.
Fred, thanks for the short dissertation on the process and it doesn't sound too pleasant. Hydrochloric acid, solvents, having to dispose of 40 gallons of it after use, the fumes when using the cutting torch from the acids and solvents, working inside a small water leg on the bottom, nahh sounds easier to build a new one.
-Ron
- fredrosse
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Re: Olfelt
"Why is it most VFT boiler tubes are welded in and not just expanded?"
Actually, I think about 90+% of VFT boiler tubes are just expanded in, with no welding. If one builds a VFT without proper dimensioning of reamed tube holes, without real boiler tubing that is smooth and of precise diameter, an expensive rolling tool, and controlled conditions, then welding becomes the only leak-proof option. I have seen several VFT boilers made with ordinary steel pipe for boiler tubes, this arrangement is very difficult to make leakproof with tube rolling.
And Ron, yes, acid work is ugly, fortunately I have outdoor facilities, and often clean up rust from open steel yard purchases with acid. It works well, but is not for everyone.
Actually, I think about 90+% of VFT boiler tubes are just expanded in, with no welding. If one builds a VFT without proper dimensioning of reamed tube holes, without real boiler tubing that is smooth and of precise diameter, an expensive rolling tool, and controlled conditions, then welding becomes the only leak-proof option. I have seen several VFT boilers made with ordinary steel pipe for boiler tubes, this arrangement is very difficult to make leakproof with tube rolling.
And Ron, yes, acid work is ugly, fortunately I have outdoor facilities, and often clean up rust from open steel yard purchases with acid. It works well, but is not for everyone.
Re: Olfelt
"...about 90+% of VFT boiler tubes are just expanded in, with no welding..."
That's what I thought. Certainly on my water-tube boiler the tubes are just expanded, no rolling over, and an expander isn't that dear, though it's all relative.
In the UK and EU the regulations appear to be stricter than some of the States where the hobby boiler rules seem quite relaxed. You'd never be able to use ordinary steel pipe here, boiler or hydraulic tube only, which are manufactured to very tight tolerances.
That's what I thought. Certainly on my water-tube boiler the tubes are just expanded, no rolling over, and an expander isn't that dear, though it's all relative.
In the UK and EU the regulations appear to be stricter than some of the States where the hobby boiler rules seem quite relaxed. You'd never be able to use ordinary steel pipe here, boiler or hydraulic tube only, which are manufactured to very tight tolerances.
Rob Lemon
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Re: Olfelt
The ASME code boiler in Nyitra is custom, I was able to choose welded or rolled-in and beaded. I chose rolled in and beaded.
I made this choice because I wanted to be able to retube easily in the future. I think in some juristictions replacing tubes does not require a credentialed boiler shop and you can do it yourself. But as soon as you talking about welding you have to have some one certified shop with the 'R' repair stamp to do it. - If you are in the US and care about being ASME code compliant. I'm trying to do that as much as I am able to.
-CB
I made this choice because I wanted to be able to retube easily in the future. I think in some juristictions replacing tubes does not require a credentialed boiler shop and you can do it yourself. But as soon as you talking about welding you have to have some one certified shop with the 'R' repair stamp to do it. - If you are in the US and care about being ASME code compliant. I'm trying to do that as much as I am able to.
-CB
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Re: Olfelt
That's certainly true in the UK: you can certainly remove tubes yourself, and replace them too - as long as the new tubes have the right specification, but as soon as you want to weld anything, it has to be done by a certified welder. The problem with that is that sometimes certified (=coded ) welders are rubbish, and it's very difficult to punish them in any way.cyberbadger wrote: I think in some juristictions replacing tubes does not require a credentialed boiler shop and you can do it yourself. But as soon as you talking about welding you have to have some one certified shop with the 'R' repair stamp to do it.
-CB
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Re: Olfelt
A common misnomer in the boiler arena is to assume a "Code Approved" welder is sufficient to get proper weld strength on boiler building, and boiler repairs.
A "Code Approved" or "Code Certified" welder is proven capable of making various welds that are examined and tested according to the Code rules. However this person does not need to know anything about the strength or size of the welds he (or she) is making. The person performing the welding need not know, and indeed often has little technical knowledge to determine the size and type of welds, the specified welding process, the filler metals specification, the post-weld heat treatment process, the weld inspection requirements, etc.
That duty is performed by the pressure vessel designer, and the designer must determine the full specification of the welds on a Code compliant pressure vessel, be it an unfired pressure vessel, or a fired boiler. The Code rules dictate that welding must meet many specific requirements, as well as stress related sizing of weld types and weld sizing, etc.
To meet Code requirements, not only a "Code Certified" welder is required, but the welds also have to be designed and specified according to the rules. Not to make any degrading comments about these welders, and they obviously pick up a great deal of empirical knowledge while welding pressure vessels together, but let us remember, the welder is usually not the designer of the weld, and to be Code compliant, the welds must be "Designed and Specified". The Boiler and Pressure Vessel Code is clear on these points.
A "Code Approved" or "Code Certified" welder is proven capable of making various welds that are examined and tested according to the Code rules. However this person does not need to know anything about the strength or size of the welds he (or she) is making. The person performing the welding need not know, and indeed often has little technical knowledge to determine the size and type of welds, the specified welding process, the filler metals specification, the post-weld heat treatment process, the weld inspection requirements, etc.
That duty is performed by the pressure vessel designer, and the designer must determine the full specification of the welds on a Code compliant pressure vessel, be it an unfired pressure vessel, or a fired boiler. The Code rules dictate that welding must meet many specific requirements, as well as stress related sizing of weld types and weld sizing, etc.
To meet Code requirements, not only a "Code Certified" welder is required, but the welds also have to be designed and specified according to the rules. Not to make any degrading comments about these welders, and they obviously pick up a great deal of empirical knowledge while welding pressure vessels together, but let us remember, the welder is usually not the designer of the weld, and to be Code compliant, the welds must be "Designed and Specified". The Boiler and Pressure Vessel Code is clear on these points.
Re: Olfelt
Fred's absolutely right, the welder can only do what the designs specify. I think the issues around welding are one of the reasons for the popularity of water tube boilers, i.e. they can be constructed without the need for welding. Obviously there are other considerations, but it certainly removes one of the problems. Also, with the general decease in small-scale engineering works, there are less coded welders around and their services are expensive, though you talk to machinists and welders nowadays and it seems that little of the money seems to trickle down to them. I'd better stop now before I get all political...
Rob Lemon
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Re: Olfelt
Quote: "I think the issues around welding are one of the reasons for the popularity of water tube boilers, i.e. they can be constructed without the need for welding."
When choosing between the two, the necessity or amount of welding doesn't really play in to it for most I wouldn't think. The VFT and WT types are two totally different steam generators. Where weight and wait is not an issue and lower steam generation per square foot is satisfactory, slower reaction and overall stability of output, the VFT is a good choice. If smaller footprint, lighter weight, higher steam generations per square foot, faster steam up and inherently less stable output is satisfactory, then the water tube type is a good choice. I think those considerations are why folks go with one or the other.
Most all boilers VFT and WT involve some sort of welding, there are only a few that involve no welding but they aren't all that common. The Monotube types and the Lune Valley two-drum.
-Ron
When choosing between the two, the necessity or amount of welding doesn't really play in to it for most I wouldn't think. The VFT and WT types are two totally different steam generators. Where weight and wait is not an issue and lower steam generation per square foot is satisfactory, slower reaction and overall stability of output, the VFT is a good choice. If smaller footprint, lighter weight, higher steam generations per square foot, faster steam up and inherently less stable output is satisfactory, then the water tube type is a good choice. I think those considerations are why folks go with one or the other.
Most all boilers VFT and WT involve some sort of welding, there are only a few that involve no welding but they aren't all that common. The Monotube types and the Lune Valley two-drum.
-Ron
Re: Olfelt
This is an excellent set of photos by KiwiNoel showing the construction of a 3 drum Yarrow type boiler
http://s1150.photobucket.com/user/KiwiN ... t=6&page=1
http://s1150.photobucket.com/user/KiwiN ... t=6&page=1
Rob Lemon