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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
API Monogram.
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
Flanges.
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.
Click
here for a caution about 6BX weld neck flanges.
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