Another way of looking at it is to consider some of the gear we need to bolt
up to, especially valves. Flanged valves invariably (I think) have the
flange holes straddling the vertical centreline. With wafer valves this is
essential to provide a path for the valve stem. If you elect for on
centreline bolts, then the valves will have to be mounted at an angle. Pumps
has straddled blot holes as well.
All advantages appear to favour straddled holes. I can think of no advantage
for on-centreline holes.
Cheers
Steve
-----Original Message-----
From: Christopher Wright [mailto:chrisw@skypoint.com]
Sent: Sunday, March 09, 2003 7:00 AM
To: ?
Subject: Re: [PipingDesign] Clarification needed regarding flange bolt h
>Well, there is a couple of reasons for that convention.
I wonder if there might not be another reason--one of those things that
may have been important at one time and not now. A bolt on a centerline
carries more stress from vertical external loads, like gravity and
seismic loading, than if the bolting were to straddle the centerline. In
any bolt pattern with radial symmetry (two or more axes of symmetry) the
geometric moment of inertia of the pattern is the same about any inplane
axis. But the section modulus (moment of inertia /fiber distance) is
lowest for the bolt on the vertical centerline, because it's located
furthest from the center of the pattern. So the bolt on the vertical
centerline carries higher stress from external loading than the rest.
For large diameter flanges with many bolts it really doesn't make much difference because the bolt on the centerline isn't that much further away than the two on either side. (Which also speaks against the 'wrench placement' argument), but for smaller low pressure systems with relatively few flange bolts, straddling centerlines might be considered good practice. On the whole the 'let's all do it one way and straddle centerlines so everything fits' argument stands up better.
Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=etlhbbS83zif727Obs7eXFoEesPrHmC6a9rE3L3EN6l6MGSAd_eJWurMip-lhJmv1IGFd7b97DE6">chrisw@skypoint.com</a> | this distance" (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)<a href="http://www.skypoint.com/~chrisw">http://www.skypoint.com/~chrisw</a>
Your use of Yahoo! Groups is subject to <a href="http://docs.yahoo.com/info/terms/">http://docs.yahoo.com/info/terms/</a> Received on Sun Mar 09 03:12:00 2003
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