14

To:
Subject: Flange pressure rating

Question:

I am currently working on a project investigating the potential for increasing the pressure rating of an existing subsea riser on a North Sea platform. The current system rating is 222bar ( 3219 psi ). We want to increase this to 325bar ( 4713 psi ). Only one component in the system, a 3-inch ANSI class 1500 flange prevents this. Do we have some potential of achieving this if we install a RX pressure energized gasket (RX35) and ensure the required bolt loads for pressure containment do not cause flange or bolt stress to exceed allowable levels. Do you have any experience with this type of scenario and can you advise of any way to technically justify this?

Answer:

The ANSI flange you refer to corresponds in dimensions to an API 3-1/8" 5M flange. If by any chance you have documentation on the flange in question, and it has the properties API requires for weld neck flanges, 45K minimum yield ( assuming the flange does have a weld neck ), you may have a case for upgrading the flange to 5M ( 5,000 psi ) working pressure without doing any more than that. The choice of ring gasket type should not affect the pressure rating. You should make sure you have B7 or L7 bolts with 2H nuts. Don't forget to consider all the other interconnecting parts and piping that will contain or control this pressure.

Click here for another related Q & A

 

Information above, and in other parts of this Web Site, may help persons who really seek to know. If you have a question, and you think WOODCO USA may have the capacity to answer it, please use our link and give us a chance to help.

WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice.  Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use.