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Bolt torque calculation for full face flange with silicone ring gasketHelpful Member! 

Danbury (Mechanical) (OP)
21 Jul 09 15:41
ASME BPV SECT. VIII, App. 2 limits raised face flange only. Could anybody be kind enough to help in bolt torque calculation for
1). The joint of 150# FF PVC Flange connecting 150# RF steel flange (B16.5) with silicone ring gasket / Bolt A307B?
2). The joint of 150# FF PVC Flanges together with silicone ring gasket / Bolt A307B?
3). Case 1) above is ok for use ASME VIII, App. 2?

Thank you very much in advance.
Helpful Member!  SnTMan (Mechanical)
21 Jul 09 16:04
Danbury, APX 2 is for design of flanges only, and really tell you nothing about in-service bolt torques, although some aspects are discussed in Apx S.

The approach you need to use is to determine the load you want on the gasket. This is based on the gross area seated versus a selected bolt stress and given bolt area. You then (usually imprecisely) match this up to a torque value.

ASME PCC-1 also disusses this subject.

Matching RF to FF flanges is usually avoided, but I suppose it can be done. Your real problem is, if I understand, plastic flanges. These will greatly limit the bolt load you can apply, again see Apx S. The flange rotation calculation may not be directly applicable to plastic materials.

You may need to do some R&D to find the bolt load that produces an acceptable seal without damaging the flanges. Very soft gaskets will be a big help, but you might have trouble retaining bolt load in service.

Regards,

Mike
Danbury (Mechanical) (OP)
22 Jul 09 8:06
Thanks for your reply. Let us discuss this topic, others are welcome to comment.
Torque value is very related to Appx. 2 that calculate Wm1 &Wm2, G, b. I do calculation based on:
1. ASME CODE: Torque=Wm*k*d/(12*Nb), Wm=max(Wm1, Wm2), k=lubrication factor, d= diameter of bolt, Nb=number of bolts
2. Vendor recommended gasket seating stress, Torque=Sv*Ae*k*d/(12*Nb), Sv=seating stress recommended by vendor, Ae=effective area=3.14*G*b
3. Max compress alowable gasket stress, Torque=Sa*Ae*k*d/(12*Nb), Sa=allowable stress
4. Bolt yield stress, Torque=Sy*k*Ae*d/12, Sy=90% bolt yield stress at design temp.
Above is for normal steel flanges of raised face only. I need to calculate torque with full face and PVC flanges.
Thanks again.
SnTMan (Mechanical)
22 Jul 09 9:39
Danbury, I am not going to go thru your calculations in detail, however I don't really agree with your use of the Code quantity "b", rather I would use the value "N", which is what I meant by the gross area seated in my previous post, this being the actual gasket area seated, whether ring or full face style (assuming flat faced flanges).

I would normally completely neglect the Code values Wm1, Wm2, W and use for the gasket load to be produced by the bolting the gasket manufacturers recommended stress times the gross seated area.

The torque values would follow from there. The use of plastic flanges is going to really complicate the problem, I believe.

Regards,

Mike

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