Flanged fitting bolt hole location

[onrush]

Dear Members,

ASME B16.5 para.6.5 requires "Bolt holes are in multiples of four. Bolt holes shall be equally
spaced and pairs of bolt holes shall straddle fitting center lines."

My question is why must paris of bolt holes straddle fitting center lines?

Would there be any problem if bolt hole is on fitting center lines?

 

[rconner]

I think it would depend on the specific fitting etc. and on the piping etc. arrangement in which it is used. For example, if you assembled your piece of pipe into the line with of course your bolt hole directly on top and then brought up a valve etc. (with bolt holes standard straddling centerline?) to be bolted to same, I believe the valve would be slightly cock-eyed and not plumb. The same thing could be true of at least some other fittings.

Even with bolt holes properly straddling centerlines it can be easy in some cases to get things fouled up, and particular care must be taken with some special fittings that might not allow free rotation, such as e.g. wall pipes embedded in concrete, and flanged reducers as discussed at

http://www.acipco.com/adip/fittings/flanged/reducers.cfm.

 

[billsumner]

I would say it is a nicety but it has some basis in stress analysis.

If you line up with a pair of bolts straddling the CL, then any moment applied due to gravity will be spread between them both.

If one bolt is on CL, then it may take all the force by itself and yield. Then loads would be distributed to the adjacent pair. A leak may occur in the gasket at the section of the yielded bolt.

Offshore, we have to deal with bolts ending up where they occur. We use a swivel ring flange to match between spoolpiece and (usually slightly rotated) pipeline.