Piping Engineering / Design Blog.


When Long Bolt Flanges Exposed to Fire

Posted by Antony Thomas at Wednesday, May 15, 2013

The Problems with Long Bolt Flanges in process pipe connections when exposed to a fire!!

It is an old slideshow on safety in Piping Design. I feel still it is worth reading and sharing.

Long Bolt Flangeless Valves

Also called long bolt valves, sandwich, or wafer valves.  Devices such as control valves, butterfly valves, check valves, etc. with no integral flanges for bolting to the pipe or vessel flanges, and thus having  exposed bolts of >3-inches.
The long bolts will likely receive direct flame contact (Impingement) if there is a fire in the area.  The direct flame contact causes the bolts to expand rapidly and lengthen, allowing both gaskets to leak product in less than 20 minutes. The leaking material then adds fuel to the fire and if under pressure it causes a large spraying fire that results in much more damage.

Standard Bolted Flanges

Direct Flame Exposure (Impingement) also causes the bolts to expand BUT it occurs significantly slower, and the leak of the material in the piping to feed the fire is through only one gasket!

Action = Identify Long Bolt Flanges

Assess Fire hazard from the contained material and location hazards.  Where possible they should be replace with normal flange valves;
The risk from fast failing Long Bolt Flangeless Valves can be reduced by wrapping the long bolts with a fire resistant material and/or enclosing the entire assembly with a 31gage (0.010") stainless steel covering.


Welded Pipe Joints obviously are the best in a fire condition, but Standard Bolted Flange Joints provide the best resistance to Fire Exposure when a removable joint is needed.
Long Bolt Flange Joints on piping in Combustible, Flammable or LPG service should not be installed in new installations and existing joints should be kept properly covered at ALL times
 and removed/replaced when possible.

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