Boiler Penetrations

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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JonRiley56
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Boiler Penetrations

Post by JonRiley56 » Tue Jan 03, 2012 11:41 pm

Hi All,

A friend of mine is working on some CAD drawings of my Boiler. I have a question about penetrations into the steam drum. I am going to run 3/4 for the steam line and intended to use 1/2 for the water gauge, feedwater, pressure relief gauge, try cocks and whistle/forced draft.

My intention was to weld sched 80 nipples into the boiler with threaded ends to attach everything. Is that the way to go ? My other option would be to weld larger diameter stock into it and tap it to take fittings. That seems less stable to me.

Thoughts ?

Jon
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Lopez Mike
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Re: Boiler Penetrations

Post by Lopez Mike » Wed Jan 04, 2012 1:27 am

On my Beckman VFT boiler they appear to have used a pipe reducer welded in place. Only a small amount of protrusion from the surface of the shell. This gives me a lot of freedom of choice in the future about how long of a schedule 80 nipple I might like to use. Also, there are a lot of extra ones on the boiler which I have plugged with ordinary pipe plugs and covered up with the insulation and lagging. You never know what you might want to do later.

With proper welding practice, such as the right bevel, it would certainly be strong enough. Black iron (mild steel), of course. No galvanized.

Mike
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Re: Boiler Penetrations

Post by fredrosse » Wed Jan 04, 2012 1:59 am

Plumbing supply houses sell "half couplings", which are typically used to be welded to tanks and such. Schedule 40 is readily available, so is Schedule 80. But, I would have to recommend that the proper welded fittings be used, the ASME Boiler and Pressure Vessel Code requires full penetration welds, and the proper fittings are beveled for welding, and held about 1/8 inch away from the pressure vessel for full penetration welding. The proper fittings are A-105 "Thread-o-lets", available at most industrial supply houses.
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A-105 Thread-o-lets.jpg
1/2 INCH AND 1-1/4 INCH THREAD-O-LETS
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Lopez Mike
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Re: Boiler Penetrations

Post by Lopez Mike » Wed Jan 04, 2012 3:01 am

So there you go! And by the time you apply some insulation and lagging, it will be nearly flush thus allowing you some choice in how you plumb things.

Mike
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Re: Boiler Penetrations

Post by 87gn@tahoe » Wed Jan 04, 2012 11:06 am

Don't want to jack this thread, but I am under the understanding that MIG welding a pressure vessel is a big no-no.. Is this correct?
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Re: Boiler Penetrations

Post by Lopez Mike » Wed Jan 04, 2012 5:03 pm

My welder, who is a certified pipeline welder, not a boiler welder, is of the opinion that the root weld needs to be done with TIG and then the filler runs can be anything that does the job.

On high pressure pipe lines, built for pressures FAR beyond our needs, the filler welds are done with simple stick work. 7018. I wonder why MIG would be a bad idea? Perhaps to keep hacks like me out of there!

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Re: Boiler Penetrations

Post by fredrosse » Thu Jan 05, 2012 12:06 am

The power piping codes allow MIG welding, however that does not mean it is a good idea for our hobby. The problem with typical home shop MIG welders is that there is poor heat penetration, and generally poor weld quality. Stick welding has much better penetration in the machines we are typically using for piping and pressure vessel welds.

It is easy to fall into the illusion that your MIG welds are very good looking, and therefore of good quality. I have MIG, TIG, Stick and Oxy-Acetylene welding equipment, and have tried to use all of them on piping, but MIG produces the worst results in my experience. Unless you have a MIG welder that uses at least 0.045 inch solid core weld wire, forget about MIG welding on pressure piping and pressure vessels.

TIG root pass welding is the best way to go, with additional passes by any acceptable welding process, assuming good weld procedures and quality inspections. Piping and Pressure Vessel welding is very different than typical structural welding.
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Re: Boiler Penetrations

Post by JonRiley56 » Thu Jan 05, 2012 12:42 am

Hi Fred,

Thanks for the info, I will definitley look to have my guys use the threadolets.

jon
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