Bolt tension as a function of tensile strength
Bolt tension as a function of tensile strength
(OP)
For determining bolt torque values, is there a thumb rule to use such as "50% of tensile strength?"
My application would mainly be flange bolts (B7).
My application would mainly be flange bolts (B7).





RE: Bolt tension as a function of tensile strength
CODE
http://www.clevelandvibrator.com/NewPDF/BOLT%20TORQUE%202%20pages.pdf
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Feeling frisky.........
www.tailofthedragon.com
RE: Bolt tension as a function of tensile strength
Understand your joint.
Determine what pre-load your joint requires, and how much variation in pre-load you can tolerate.
Determine if torque control can attain that level of tolerance, or select a better method of pre-load control.
Select fasteners.
RE: Bolt tension as a function of tensile strength
My experience with bolted joints shows many rules-of-thumb:
90% of yield
90% of proof
75% of tensile
etc.
Rules of thumb really aren't useful.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolt tension as a function of tensile strength
RE: Bolt tension as a function of tensile strength
RE: Bolt tension as a function of tensile strength
RE: Bolt tension as a function of tensile strength
The zerofast website article by Joe Greenslade shows values based on 75% of the YIELD strength, not 75% of the tensile strength.
RE: Bolt tension as a function of tensile strength
RE: Bolt tension as a function of tensile strength
Mint julep has it right, attack things in this order and you'll be OK
RE: Bolt tension as a function of tensile strength
Also, what is the feeling on bolt preload tension for a self-energizing gasket such as an o-ring? For this type of flange design, I feel a bolt preload tension greater than the bolt design allowable at temperature would suffice. i.e. use a 30 ksi preload tension for SA-193 B8M Cl,2 bolts with an allowable of 22 ksi at 250 deg F. Any feedback would be greatly appreciated.
RE: Bolt tension as a function of tensile strength
Excellent response. I get the same question as you all the time and feel the same frustration. We have shown that over 100 variables effect the end clamp load in a joint and customers expect us to be able to give them a torque recommendation when they cannot even provide us with a target clamp load!
In fastening, the rules of thumb have caused many major failures becuae they fail to take into account any individual considerations present in a particular situation.
Tighter is better, but only until it causes embedment, joint collapse and flange bending......
Dick
RE: Bolt tension as a function of tensile strength
This post is dating back a bit and understand your frustration. I infact am guilty of asking our bolt manufacturer to help determine proper bolt torque tightening for each fastener we purchase from them.
Using T=KFD, we should be able to calculate all we need. However how do we know what target clamp load we want?
RE: Bolt tension as a function of tensile strength
The target clamp load should be sufficient to resist the forces applied to the joint (tension, shear, bending, torsion, etc.). Do you know what forces are applied to your joint(s)?