Boiler bushings

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jlakes85
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Boiler bushings

Post by jlakes85 » Sat May 20, 2017 6:06 pm

Hi all,

I'm currently building a buckwalter Shay boiler using an all TIG process. Concerning half couplings used for the various bushings, are the rules for joint gapping the same as for the sheets, i.e. about 0.125 all around or is a narrower gap permissable? Thanks again.

Regards,

Jlakes85

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Marty_Knox
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Location: Michigan, USA

Re: Boiler bushings

Post by Marty_Knox » Sat May 20, 2017 8:31 pm

You'll never locate them accurately with that kind of gap. I'm at home, so I don't have my reference books handy, but Monday I will post the relevant information.

jlakes85
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Re: Boiler bushings

Post by jlakes85 » Sat May 20, 2017 9:30 pm

Hi Marty,

Sounds good, much appreciated. Once I tracked down the appropriate class 3000 couplings from McMaster and crossed referenced to the drawing, I started to scratch my head..1.150 hole for a 1.125 OD bushing e.t.c. Gonna really have to crank the machine up to get that keyhole going..

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Marty_Knox
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Re: Boiler bushings

Post by Marty_Knox » Mon May 22, 2017 8:06 am

The relevant wording is from Section 1 of the ASME code, PW-16.5 Internally threaded fittings less than NPS 3 (3" pipe) may be attached by a fillet groove weld from the outside only.
My scanner isn't working so I can't post the illustration.

jlakes85
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Re: Boiler bushings

Post by jlakes85 » Tue May 23, 2017 7:14 am

Hi Marty,

Sounds good. Thank you again for digging this up. I'm surprised that the code allows a fillet groove up to that large of a pipe size. It does make life a whole lot easier, as well as my sanity overall in second guessing hole size call outs as compared to the class 3k coupling OD's.

The Feb 89 issue of Live Steam as well as the Oct 87 issue of Modeltec did a good job of drilling into my head the general dangers and prohibition of using fillet welds on a pressure vessel.

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Fender
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Re: Boiler bushings

Post by Fender » Tue May 23, 2017 8:29 am

Marty,
Could you clarify what a "fillet groove" weld is? I looked up images of different weld joints and didn't see that one.
Thanks.
Dan Watson

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Marty_Knox
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Re: Boiler bushings

Post by Marty_Knox » Tue May 23, 2017 8:48 am

fillet groove weld.pdf
(97.58 KiB) Downloaded 265 times
Fender wrote:Marty,
Could you clarify what a "fillet groove" weld is? I looked up images of different weld joints and didn't see that one.
Thanks.

jlakes85
Posts: 209
Joined: Thu Feb 23, 2012 6:07 am

Re: Boiler bushings

Post by jlakes85 » Tue May 23, 2017 9:55 am

Hi marty,

Looks good. Judging by the PDF, I would only need enough of a hole clearance to slip the bushing through

Bastelmike
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Re: Boiler bushings

Post by Bastelmike » Tue May 23, 2017 1:03 pm

Hi Marty,

thank You for the explanations and sketch.

Being from the metric world, I'm a bit surprised about that 1/4" dimension. 1/4" for let's say a 1/2" pipe to a pressure vessel Looks a little oversized to me.

My memories about the German pressure vessel regulations in effect until 2000 that the weldment dimensions were very dependent on the size of the opening (i.e. pipe size). Forces involved are correlated to the opening area so weldment should be stronger with increasing pipe size.

Mike

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Marty_Knox
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Re: Boiler bushings

Post by Marty_Knox » Tue May 23, 2017 1:45 pm

That 1/4" dimension is for 3" NPT. The requirement is that the weld thickness be equal to the wall thickness of Schedule 160 pipe. For 1/2" NPT that would be 3/16". Another rule says the welds for less than 3" pipe are exempt from the size requirements as long as there is enough weld to provide the required strength.
The rules were not designed for our size boilers.

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Fender
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Re: Boiler bushings

Post by Fender » Tue May 23, 2017 2:50 pm

Interesting that the weld on the left side of the coupling on the drawing is different than the one on the right. Does this mean that either is acceptable?
Dan Watson

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Marty_Knox
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Re: Boiler bushings

Post by Marty_Knox » Tue May 23, 2017 2:52 pm

Yes it does. Things like the angle are 'non-critical variables'.

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