Flange API 6A Design 2

[ASMS81]

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.

 

[yudhichen]

Dear ASMS81,

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

 

[ricklts]

I'm not sure why you are checking bolt stress on a 6A flange. Current edition specifies bolt loads as 55% Ys applied. Will you be going higher? Changing bolting materials or flange materials?

Rick

 

[Gilmiril]

One important point is that the current 20th Edition of API 6A is also ISO 10423:2009 (Modified). That 'modified' is important because differences between API 6A and ISO 10423 are not identified in the body of the spec. Instead, if you are working to API 6A, you must apply all changes that are detailed in Annex O. Note also that Annex O is updated with each release of new addenda and errata; so far, there have been Errata 1, 2, 3, 4, and 5 as well as Addenda 1, 2, and 3, so you must make sure you're using the latest Annex O.

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.

 

[Duwe6]

"Bolting stresses, based on the minimum cross-sectional area. . . "
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.

 

[Gilmiril]

I agree that it would be the root area (with your noted exception), but my point is that if one is quoting from a standard, it's important to quote the correct wording. API 6A can be confusing because people often forget to check Annex O. In this case, there's no harm done, but in other cases, there could be.