Boiler questions

[barts]

For those of us doing our own welding, if you don't have a TIG machine handy for the root pass (nice - no flux to grind out) the traditional method is to use 6010 rod using DC w/ electrode positive. You do need to space the fitting out as suggested to ensure maximum penetration, and of course remove anything that isn't sound weld metal before the next pass - typically, 7018 'drag' rod (also used w/ DC and electrode positive). 7018 should be kept in a rod oven; at a minimum, bake it in an electric oven @250 for a hour.

I used these techniques to weld Otter's boiler more than 15 years ago. For pictures see http://smaalders.net/bart/boiler.html

For those of you wearing glasses, this is one area not to use variable focus length (progressive) or bifocal lenses. Welding is much easier if you can use the entire lens, and an auto-darkening helmet with an ample view port really helps. Since we're talking about stick welding, not MIG, a fan (or smog hog, for the fortunate) to blow/suck weld smoke away is a really good idea.

- Bart

[Jack Innes]

There is a great deal of good information coming forth on this. Thank you. I am learning!

My boiler has an upper horizontal drum 6" diameter X 15" long. It has a steam dome 1 7/8" outside diameter X 6" high with one 3/8 npt outlet 3" from the top, facing to the rear. The legitimate plumbing will cover the top most part of the drum to the rear & the stack support covers the front portion of the drum.

1/ Would it be permissible to add a 1/2" npt penetration near the top of the drum with a thread-o-let modified to produce a 45 degree exit? This would be plumbed through the casing to a 45 degree el. thus giving a vertical position for the safety valve.

2/ Would it be wise to add a second similar penetration on the other side that could feed the whistle & gauge? This would leave the throttle valve on its own penetration from the steam dome. The other two would not have the advantage of the steam dome.

3/ While the boiler is apart would it be permissible to add support lugs to properly attach the stack? If so what would be the procedure? I envision making something like the weld-o-let with a 5/16 or 3/8" SAE thread in perhaps a 1 1/2" disc welded in place to avoid angular stress on the weld joint.


I am certainly not questioning the point but why does the safety valve need to be on its own penetration? I am sure there are others that need education on this as well.

Thank you,
Jack

[johnp]

Jack, check your emails

[fredrosse]

MIG welding on a pressure vessel is generally not good, better to grind down the weld and re-weld with stick welding. MIG is OK for thin metal welding because it does not have good penetration. But for that same reason it is not generally good for pressure vessel welding. MIG machines that can use 0.050 or 0.060 wire diameter are the minimum for small pressure vessel connection welding, and these are industrial machines, not the machines we steamboaters can typically access.

"1/ Would it be permissible to add a 1/2" npt penetration near the top of the drum with a thread-o-let modified to produce a 45 degree exit?" ANS Thread-o-lets with the 45 degree tilt are comercially manufactured already.

2/ Would it be wise to add a second similar penetration on the other side that could feed the whistle & gauge? ANS: Yes

3/ While the boiler is apart would it be permissible to add support lugs to properly attach the stack? If so what would be the procedure? I envision making something like the weld-o-let with a 5/16 or 3/8" SAE thread in perhaps a 1 1/2" disc welded in place to avoid angular stress on the weld joint. ANS: can you post a sketch, having trouble envisioning your proposal.

[fredrosse]

"why does the safety valve need to be on its own penetration?"

The best answer is that the boiler code clearly requires it, and we should follow these rules even if it is not immediately apparent why. On several occasions I have questioned ASME rules, only to discover later the good reason for the rules, and so far the boiler code has always been correct.

I think the reason for this rule is as follows: The safety valve senses its inlet pressure, and that very pressure actuates the opening of the valve. If there are other connections on the line that feeds the safety valve, then some flowing conditions could reduce the pressure that the safety valve senses, and hence the safety valve may not function properly. I know some might say they would not have much flow in another connection, so additional connections to the safety valve pipe should be OK. Maybe so, but the same logic could be used for putting an isolation valve between the boiler and the safety valve: "I will always be sure the valve is open whenever I run the boiler" . We should all know how dangerous (and illegal) that move would be!

[Jack Innes]

3/ While the boiler is apart would it be permissible to add support lugs to properly attach the stack? If so what would be the procedure? I envision making something like the weld-o-let with a 5/16 or 3/8" SAE thread in perhaps a 1 1/2" disc welded in place to avoid angular stress on the weld joint. ANS: can you post a sketch, having trouble envisioning your proposal.[/quote]

Thank you Fred for the information. I need to put dismantling the boiler off for a while until a few other projects are put to bed for the winter. I am unable to post a sketch but my question is essentially what is the acceptable method of attaching the stack and perhaps a gauge board to the boiler? At present the stack is supported by the outer, thin shell of the boiler with no guy wires. There is a band around the circumference of the boiler that holds the stack base in place.