BIG companies, or their contractors, make mistakes all the time. Should I say, Especially BP? No, because then you might think I'm picking on BP only, when Shell was up there in the Arctic hauling around a drilling rig with no backup tugs. In fact I tend to think that the possibility of making mistakes increases with the size of the company, as does size of the mistake!

Many engineers outside the USA are not so familiar with the MMS pipeline high strength material specs. They tend to think only of plant piping and ASME B16.5
I doubt anyone did any calculations.

What they probably want is an A694 Grade 65 flange, then they said B16.5 instead of specifying MMS SP-44.
That mistake happens all the time. It is a tiny bit unusual for high strength steel to be actually needed for 6" diameter, but certainly might be under unusual circumstances.

Thanks for your reply, BigInch. I raise this question is because those F65 flanges supplied were approved by an authoritative Third-Party Inspection corporation appointed by the customer. To my astonishment, they just reviewed the MTR and checked some dimensions. My understanding is A694 material is only applicable to MSS SP 44 flanges with a size 12 and larger up to 900#. Your information is very helpful. Yes. we rarely do any calculation but manufacture to relative standards or Codes. Only for 1 or 2 times, a calculation and design work was required to take as per TAYLOR FORGE's "modern flange design bulletin 502" which is very painful....

Hebei Metals Industrial Limited
www.hbmetals.com

The use of A694 is common when mating flanges to higher grade pipes commonly seen in the pipeline world as opposed to the piping world.

Given that the flange dimensions are identical between 16.5 and MSS-SP-44, it is really only a material issue and the order maybe should have read dimensions to ANSI B 16.5.

However these flanges are so commonplace and used so frequently that it is not surprising that they are referred to as this.

Interestingly enough, I have a copy of BP flange specs from a few years ago for higher grade material which actually references ISO 15590 as its reference spec.....

X 65 6" is a little unusual, but might just be a tee or branch connection and not the main pipe itself.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

A694-F65 flanges are very common in sizes from 1" thru 12" for Offshore Production systems. I am not familiar with requests for supporting design calc's, I think because as Big Inch says, the dimensions are identical, and it's just an issue of using a higher strength material than is normally encountered. We are beginning to see requests for even higher strength materials to be accompany X70 and X75 tubulars.

It's true. I have noticed that higher pressures are seen more and more these days near the deeper wells, which can require more of the higher strength materials for the smaller diameters. Can't get much closer to those high pressures than at the offshore platforms.

"Given that the flange dimensions are identical between 16.5 and MSS-SP-44, it is really only a material issue and the order maybe should have read dimensions to ANSI B 16.5."

I used to think the same thing until recently trying to procure an odd-ball size 22" 600# flange per ASME B16.5. Turns out there is no such thing. 22" flange standards only exist under MSS SP44.

The wonderful world of industry standards....