Weld necks on 6BX flanges
Can I order an API,
4-1/16 10K x 4"
XXH weldneck flange having the weld
neck end 4-1/2” O.D. and the bore the same as 4" XXH pipe? Does the flange meet
API Spec. 6A if forged from 4130,
75K material? I understand that you
can order any API 10,000 psi flange with an optional weld neck and bore,
as long as it's made from certain materials and you have a qualified
welding procedure to join the flange and pipe material.
I have someone asking me if it’s OK to weld
a flange with these dimensions to 4” XXH pipe, when they see the
published “Standard Dimensions” of a 4-1/16” 10K flange weld neck
and I.D. does not match 4" XXH pipe.
Operators often order 4-1/16" 10K
( 10M ) flanges with non-standard weld necks, sized to match standard
pipe sizes. Operators ordering such flanges
realize that their flange’s working pressure will not exceed that of the
matching pipe they have selected. These flanges usually cannot bear the
No matter what you do, the working
pressure of any system equals the working pressure of its lowest
pressure component. If the pipe won't stand the pressure, any attached
flange and welding procedure used to attach it will not increase the
strength of the pipe. Note also that 75K material exceeds that required
for 10,000 psi. working pressure flanges, so unless you have data on the
mechanical properties of the particular flange you have, you cannot count
on the material exceeding 60K.
When you vary from
dimensions and material requirements specified by recognized standards,
e.g. API Spec 6A, then you should seek competent engineering advice.
For more information
about joining flanges to pipe by welding see:
About Weld Neck
Weld Neck Flange Attachment.
Q & A 37 API Flange Weld Neck and Matching Pipe I.
Q & A 45 API Flange Weld Neck and Matching Pipe II.
here for a caution about 6BX weld neck flanges.