A193 B7 vs B16 regarding fire resistance

[ansys1000]

Hi

At our plant (chemical process plant) we have choosen to install B16 bolts in a certain area that contains our most flammable media with the ground that the B16 will resist fire better and therefore prevent flange leakage. Is it common practice to use B16 in this way? The design temperature is max 300C. The question really is if the B16 bolt will do a better job in case of a fire than B7...? The piping itself is built in A106 grade B.

I would really appreciate som thoughts about this!

Best Regards
Thomas

 

[mrfailure]

B16 is rated (at least by suppliers)for use to 550 deg.C. B7 is rated to lower temperatures of 480 deg.C (Choice Fasteners) or 400 deg. C (PIF), depending on source. So theoretically, B16 will better hold up in a fire though either will meet your design temperature requirement.

Aaron Tanzer

http://www.lehightesting.com

 

[stanweld]

It is not common practice to use B16 for that purpose.

 

[ricklts]

Most elect to use B16 when elevated operating temperatures necessitate bolting with higher Ys values than B7. But in your case, and without definitive information concerning temperature zones, thermal transit times or such, I don't think there will be any difference in results. In either case, your flanges will be subjected to additional external loads due to thermal expansion of the joint and components. Given sufficient time at sufficient temperature, the joint will experience higher leakage potential, some of which may be due to increased bolt load rotation across the gasket surfaces if bolts of higher temperature capability are installed.

Just a note based on experience in many petrochem, fossil and nuclear sites for 30+ years.

 

[jtseng123]

Ansys,
We have designed so many gas, oil and petrochemical plants, and never worry about this problem. We never see any B16 used for carbon steel flanges in hundreds of thousands of connections.
Bolting selection is based on compatibility with flange materials and galling problem. You don't want bolting has higher thermal relaxation than flange. Have you cheeck which one has higher thermal relaxiation ?
B7 in our pipe spec, is even used for 304H SS flange for high temp service, and has been discussed in this forum in the past.
In case of fire, your CS flange and pipe will be distorted and gone first, why worry about bolting ? Going by industry common practice of using B7 is the way to go.