Re: Clarification needed regarding flange bolt h

From: <Christopher>
Date: Sat Mar 08 2003 - 12:59:00 EST

>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=BV-uDo_9RMwTjT6wypkO_Bk9nhytnGyXUPrJqU6YU90EIu2ba9GJVkiZRWWro7po6_PpgZ3jRIkHt9XarBA">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> Received on Sat Mar 08 12:59:00 2003