Bolt Design Stresses - ASME B31.3
Bolt Design Stresses - ASME B31.3
(OP)
Alright, somebody please correct me if I am wrong here.
ASME B31.3 302.3.1 states "The allowable stresses defined...shall be used in design calculations unless modified by other provisions of this code." It then goes on to state that the design stresses for bolting materials are as per Table A-2.
For A193-B7 studs at room temperature, Table A-2 lists a design stress of 25,000 psi. This is much lower than "industry standard" bolt stresses used when bolting up flanges.
For example, ASME PCC-1-2000 "Guidelines for Pressure Boundary Bolted Flange Joint Assembly" Table 1 "Target Torque Values for Low-Alloy Steel Bolting" contains a general note stating that the values shown are for a target prestress of 50,000 psi (root area). I haven't looked at why they have used the root area rather than the tensile stress area, but for a 1/2" bolt 50,000 psi applied to root area corresponds to about 44,300 psi on the tensile stress area. This still substantially exceeds the 25,000 psi that ASME B31.3 would seem to permit for this bolt.
That is just one example, but my experience indicates that virtually all the owners and gasket manufacturers recommend/require bolt loads higher than the code design stresses. Is there a section of B31.3 that permits the use of these bolting materials at such "high" stresses?
Or does everyone just say it's easier to just crank up the torque on the bolt than to perform accurate calculations for every boltup out there, and ignore the code.
Maybe I'm way out to lunch here, but when I talk with some of our senior folks about the issue, I get a lot of blank stares...
ASME B31.3 302.3.1 states "The allowable stresses defined...shall be used in design calculations unless modified by other provisions of this code." It then goes on to state that the design stresses for bolting materials are as per Table A-2.
For A193-B7 studs at room temperature, Table A-2 lists a design stress of 25,000 psi. This is much lower than "industry standard" bolt stresses used when bolting up flanges.
For example, ASME PCC-1-2000 "Guidelines for Pressure Boundary Bolted Flange Joint Assembly" Table 1 "Target Torque Values for Low-Alloy Steel Bolting" contains a general note stating that the values shown are for a target prestress of 50,000 psi (root area). I haven't looked at why they have used the root area rather than the tensile stress area, but for a 1/2" bolt 50,000 psi applied to root area corresponds to about 44,300 psi on the tensile stress area. This still substantially exceeds the 25,000 psi that ASME B31.3 would seem to permit for this bolt.
That is just one example, but my experience indicates that virtually all the owners and gasket manufacturers recommend/require bolt loads higher than the code design stresses. Is there a section of B31.3 that permits the use of these bolting materials at such "high" stresses?
Or does everyone just say it's easier to just crank up the torque on the bolt than to perform accurate calculations for every boltup out there, and ignore the code.
Maybe I'm way out to lunch here, but when I talk with some of our senior folks about the issue, I get a lot of blank stares...





RE: Bolt Design Stresses - ASME B31.3
This has nothing to do with the stress the bolts are torqued up to during installation. This concept is described in Section VIII, Div 1, Appendix S.
If you search, you will find other threads on this topic.
RE: Bolt Design Stresses - ASME B31.3
RE: Bolt Design Stresses - ASME B31.3
RE: Bolt Design Stresses - ASME B31.3
RE: Bolt Design Stresses - ASME B31.3
RE: Bolt Design Stresses - ASME B31.3
http://www.boltscience.com
Really intrested?
http://www.hexagon.de/dose/dose1e.htm
RE: Bolt Design Stresses - ASME B31.3
Based on experience, 25 ksi bolt stress is low if you are looking for a leak free joint using B7 studs, however how high do you go to ensure a leak free joint and not damage your equipment? Appendix S suggests that higher bolt stresses may be required at times.
A reasonable bolt stress limitation to consider is the flange stress calculated using Appendix 2 methods. What I have done extensively is substitute 90% of the amb. yield strength of the flange as the allowable material limit and backward calculate the corresponding bolt stress. You will find that the bolt stress for most B16.5 flanges will work out to be 30-45ksi using this method. I have witten bolting specs for entire petrochemical plants using this logic in conjuction with controlled bolting field practices. I rationalize using greater than ASME material allowable stress when examining the intent of Appendix S. Where this method trips up is when you try to calculate bolt stress using App. 2 methods on some of the alternative flanges, such as ASME B16.47B flanges. You will find that the bolt stress may be in the low 20 ksi range, which is intolerable to me.
ASME PCC applies across the board bolt stress values to a bolt size. This is unreasonable considering the gasket area to bolt area on B16.5 flanges is all over the map. Gasket manufacturers wind gaskets within a class to a similar density, which means that gaskets within the same class will seat at the same stress. The bolt stress to achieve that same gasket stress between any two flanges is different, which is why ASME PCC fails for me ginving target stress by bolt size with no consideration for gaskets or flange material strength.
Another thing to consider is bolting methods, and to me, the methods of bolt-up is as important as the stress.
Hope this creates some thought, Rick
RE: Bolt Design Stresses - ASME B31.3
First the codes are design codes not assembly codes perse. therefore the stress values stated are for for design purposes.
However between design and the real world lies many considerations. I strongly suggest a read on this book http://
In it Dr. Bickford discusses the situation quite clearly. The bottom line is bolt-up stresses are not the same as design stresses and may be quite higher in nature.
Regards,
XHPIPE
RE: Bolt Design Stresses - ASME B31.3
Q: What load should be used in FEA, calculated bolting load from the code or the bolting pre-load?
RE: Bolt Design Stresses - ASME B31.3