Re: [PipingDesign] Flange Bolt Array Positioning

From: <Gang>
Date: Sun May 21 2006 - 00:47:00 EDT

Dear friends,
I remember to have addressed this issue some time earlier as well. Let me recall the points once again. 1. Instrument tap offs normally demand the orientation to be straight vertical. If a bolt happens to be ON AXIS, this will have to remain tilted. The same rule governs them for the horizontal taps also. 2. Valve actuators (say, in case of a ball valve or a butterfly valve) require the option either to be vertical or horizontal. A straddled bolt line easily permits this.
3. The above logic applies to a vertical face of flange as well, lest the orientations would go off the axes and grids (get tilted).
4. The number of bolts is always multiples of 4, so the situation remains the same in 12, 3, 6 and 9 O’clock positions.
5. Take the case of Class 300 1.5 inch flange and 2-inch flange.

a. 1.5 inch size has 4 blots of ¾.
b. 2 inch has 8 bolts of 5/8.
c. The intermediate number of 6 is not adopted.
d. The number of bolts selection went in favour of 8

with a reduced bolt size.
I hope this clarifies the doubt!
Regards.
C. V. Gangadharan,
Abu Dhabi.

• Christopher Wright <chrisw@skypoint.com> wrote:

>
> 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
> chrisw@skypoint.com | this distance" (last words
> of Gen.
> .......................................| John
> Sedgwick, Spotsylvania
> 1864)
> http://www.skypoint.com/~chrisw/
>
>

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