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Quantity of bolts for a flange

Quantity of bolts for a flange

Quantity of bolts for a flange

I have a tank with a flange that will have a lid over it. The lid will sit flush with the tank and plans are to drill holes through the lid and flange to seal the box with nuts, bolts, and apply a gasket. The tank is not intended to hold pressure, I just want it to be sealed.

My question is that if I should consider any resources before just throwing out a quantity of bolts that each flanged end will have. I don't want to have too many as for application purposes the lid we be removed periodically and I don't want it to be too time consuming. Maybe there is a general rule of thumb for number of bolts needed per length of a flanged end?

Any info or resources much appreciated.


RE: Quantity of bolts for a flange

Consult ASME B16.5.

Or, I'll assume you'll just use a red rubber gasket, then the following bolts would be good based on NPS

1 - 3" - 4 bolts
3.5 - 8" - 8 bolts
10 - 14" - 12 bolts
16 - 18" - 16 bolts
20 - 24" - 20 bolts
30" - 28 bolts
36" - 32 bolts
42" - 36 bolts
48 - 54" - 44 bolts
60 - 64" - 52 bolts

Place evenly around flange. Incrementally tighten and re-tighten after a few hours to further ensure long leak free service.

RE: Quantity of bolts for a flange

Ah sorry did not even look at attachment, just assumed it was circular.

From looking at it I would put about 5 per side or extrapolate from the chart I gave above keeping in mind how often you want to disassemble it, and that for your gasket (assuming a rubber one) to make a decent seal it would need about 200psi on it.  

RE: Quantity of bolts for a flange

1.   Decide on your desired ID of the flange.

2)  Find the next larger STANDARD pipe 150 lb (low pressure) flange that will meet this requirement.

3.  Purchase the "standard 150 lb flange, sch 40 pipe, and blank flange" (for the cover) that will fit.  

This will be the least cost, fastest assembly.   Yes, it be stronger than needed.  But no cutting, fitting, machining, drilling, calculating, checking, correcting!!! or other problems.   

RE: Quantity of bolts for a flange

Hi racooke1978

Its a rectangular tank not a circular one.


RE: Quantity of bolts for a flange

1.  You have essentially no internal pressure to withstand.  Thus, from the "standard round pipe flange" catalog lists, determine the "average distance between flange bolts" and the typical diamter bolt used (for example, 3/4 inch bolts in 7/8 holes for 10 and 12 inch diameter pipe flanges that are 16 and 19 inch diameter) for several typical low pressure standard pipe flanges (150 lb steel flanges).

2)  You now know what thickness flanges do not bend (distort) under internal pressure greater than what you expect to see, what size bolts work (develop adequate clamping pressure) under worse conditions that what you will see, and thickness blind flanges don't distort under pressures greater than what you expect to see.   

3) for your rectangular flange, use the appropriate size bolt and interval between bolts.      

RE: Quantity of bolts for a flange

Is the cover the "top?"

The flange is 1/4 " thick.  I wouldn't tap it for fasteners over 1/4 inch. If maintenance is a concern then installing studs into the tapped flange and having some holes slotted would allow leaving some of the nuts and washers in place.

A piano type hinge along one edge (set to accomadate the gasket thickness) would mean only 3 sides would have to be bolted.

If the cover had 2 edges flanged then only 2 edges would need bolting.

If the cover was flanged and there was a piano hinge along one edge then only one edge would need bolting.

If three edges were flanged and the 4th was a piano hinge then one bolt on the edge or the corners opposite the hinge might suffice.

If all 4 edges of the cover were flanged, a single bolt in the center might suffice.

RE: Quantity of bolts for a flange

i think that you have to specify the entire joint, not just the bolt number and size.

My guess:

Eight bolts, 3/8" size with full nuts & flat washers.

One bolt in each corner, one in the middle of each side

3/16 thick red rubber gasket.....

Now, if you intend to open this "mystery box" periodically, I would consider other, more expensive "quick opening fasteners.

My opinion only



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