Flange API 6A Design
Flange API 6A Design
(OP)
Dear all
I need to check an API 6A flange, so while verifying the bolt stress I am not sure about which area I should use. Normally ASME uses the bolt root area but I heard that by using API I should use another.
Any idea?
Thanks in advance.
I need to check an API 6A flange, so while verifying the bolt stress I am not sure about which area I should use. Normally ASME uses the bolt root area but I heard that by using API I should use another.
Any idea?
Thanks in advance.





RE: Flange API 6A Design
As i look at API6A (right now I'm using 20th edition), on sub-clause 4.3.3 it clearly mention that bolt stress are based on thread root area.
The thing that might be different area probably came from Annex D when you wanna calculate bolt torque.
Annex D said that the stress calculation (it belong to the formula stated on that section) are based on stress area, and not thread-root area as required for stress calculation in 4.3.4.
Hope this help.
Regards
Yudhi
RE: Flange API 6A Design
Rick
RE: Flange API 6A Design
That said, yes, subclause 4.3.4 (Closure Bolting) states, "Bolting stresses, based on the root area of the thread, shall not exceed the limit given in Equation (9):"
But Annex O instructs us to replace the above with, "Bolting stresses, based on the minimum cross-sectional area of the bolting, shall not exceed the limit given in Equation (9):"
So no, the root area is not necessarily the design requirement.
RE: Flange API 6A Design
Sounds like Thread Root to me. Unless the shank is greatly reduced in diameter from the major diameter of the threads, the minimum cross-section is the minor diameter; i.e. the thread root diameter.
Don't over-think the problem. Yes, quality bolts fail by the heads literally blowing off sky-high [and I know this from lab bolt testing]. BUT, API 6A wants you to be more conservative and use the thread root for allowable loading. Simple.
RE: Flange API 6A Design