Xmas Tree - Limits for API 6A classes

[skizzato]

Hi everybody...
With reference to thread408-266082, I have a similar issue.
I am designing the surface facilities of a wellhead, with the tree itself out of my scope.
Design conditions provided by the Customer (who is Himself engineering the Xmas Tree) are 380barg @ 115 degC.
Therefore I am going inside my s.o.w. with ASME 2500#.
Now my issue.
The Customer is telling me that Tree flanges (which I should connect to) are API 5000#.
When I highlighted that given design conditions are outside the limit for this class, the Customer replied that the flanges are standard API 5000#, but tested and certified for API 6500#.
Does anyone know if this is acceptable for API 6A?
This because couter-flanges are in my scope and I do not know which corner i should bang my head against (to me flanges should be API 10000#).
Any help would be greatly appreciated!

 

[SPDL310]

I believe that you are correct the MAWP on the flange is above 5000 psig then it should be on a de-rated 10,000 psig class flange, therefore the seal ring bolt pattern ect. should be off of a 10k flange. The thread you referenced does stat that uprating is acceptable however it is not a recognized API class and will not have an API monogram. If the flange is approved by an agency such as DNV, ABS ect. it is safe to use. I would ask to see design clacs for the flange in order to verify safety and start your design.

 

[skizzato]

Dear SPDL310, thanks for prompt feedback. I did ask my Customer the drawings of the flanges on the Xmas Tree and received drawing are exactly matching API 5000# dimensions (bolting holes and flange thickness). What I was wondering is if API foresees the possibility (which I did not find in API 6A) to overtest a API 5000# flange in order to certify it for a pressure greater than the 34.5Mpa foreseen in API 6A.
If this is possible I would do exactly the same in my s.o.w with mating flange.
Thanks again!

 

[LittleInch]

I've seen this before where API 6A flanges can be certified for use at a higher MAWP by examination of material certificates, testing to a higher pressure and someone signing all this off.... I recall hearing you can test to 2 x the normal rating which when you then divide by the normal X 1.5 for hydrotest gets you close to the 6,500 psi limit quoted.

However it remains a #5000 flange, but approved to operate at 6500 psig.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Gilmiril]

API 6A used to specify the minimum hydrostatic test pressure as 2x the rated pressure for 2000-psi flanges (up to 13 5/8"), 3000-psi flanges (also up to 13 5/8"), and all 5000-psi flanges. For the 5000-psi flanges, this was revised downwards to 1.5x the rated pressure. So yes, 5000-psi flanges can be tested to 10,000 psi, which would be suitable as a hydrotest pressure for a rating up to 6667 psi (more typically rounded to 6650 psi).

But in order to actually rate such a 5000-psi flange to 6650 psi working pressure, it requires an engineering review to ensure suitability. And as previously mentioned by SPDL310, this would not be API monogrammable.

 

[yudhichen]

Based on your customer reply, looks like they use x-mas tree with (working) pressure rating 6,500PSI on the flange right to the boundary where you start to design the facilities.
They mention "flanges are standard API 5,000PSI, but tested and certified for API 6,500PSI",
means those flange was designed by using API 6A 5,000PSI dimensions.
hence, you can use this information for designing the mating flange as the boundary of your equipment facilites.

please remind if there's a note if you want to mate API flange and ASME flange.
you can check on this:

http://www.woodcousa.com/flg_cross_ref_main.htm

The recognized working pressure (WP) based on API6A are 2k, 3k, 5k, 10k, 15k, and 20ksi.
If tree manufacturer design it with those WP, then the they can monogrammed the tree.

For this particular case, 6,500PSI is not mention on API6A, as per SPDL310 said, its not monogrammed.
But still, tree manufacturer can produce 6,5k WP rating based on customer demand provided they can verify their design can fit for purpose.
(verification consist of pressure test, calculation, etc).

Hope this helps.

 

[skizzato]

Thanks to everybody for the very useful info.
I will look what should be done practically for the approval to operate @ 6500 PSI.
Last doubt remains the responsibilies in case of failure and major accident as I am now operating outside the code.
In principle it would be like taking a carbon steel flange ASME #150, test it @ 45 barg and, if it does not fail, state that it is suitable to work @ 30 barg. ASME B 16.5 gives me much lower figures, therefore I would be working outside the code and in a big mess in case of failure....
Thanks again!

 

[LittleInch]

That's why you need a copy of the certification your client has!

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way