Re: Flange Bolt Array Positioning

From: <Christopher>
Date: Sat May 20 2006 - 15:32:00 EDT

On May 20, 2006, at 4:02 AM, Paul Bowers wrote:

> The question is based on flanged connections and is about the holes for
> the bolts. Why are holes on a flange never positioned on the vertical
> centerline?

The story I was told is that such positioning forces the topmost bolt to carry more stress when the attached pipe is subject to bending about a horizontal axis. This is true but I can't imagine it's significant for flanges with more than 4 bolts. With 4 bolts the difference in bending stress is about 30%; with 8 bolts the difference is less than 10%

Since the number of bolts on standard flanges is always a multiple of 4 straddling the vertical centerline also makes the bolt pattern straddle the horizontal centerline, so bolt stresses from horizontal loading would also be lower. Maybe the lower stress argument is correct, but I still can't imagine that it would make a lot of difference.

I think I overheard someone say that it was for accessibility from underneath, but again, for more than six bolts it isn't going to make much difference.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=n4fndr2ZsZS5T4HArdjMdd47YHMVXEsNQ9OTSQugQ6pDmsTFoi4Lz0I5c8oAxMi-2JJCW9ja0_dKZndz">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 May 20 15:32:00 2006