Dear members,

ANSI DN500 #300 WN flange (SCH40) is to be connected to mating flange ANSI DN500 #300 WN(SCH 80). The only difference for two matching flanges is the schedule, so the inside diameter will vary by around 20mm.

Please advise if there is any leakage or installation issue when two flanges has different inside diameter.

Note that the flange will be experiencing high external forces. The calculation shows the hub stress and leakage are on border line, with schedule 40 flanges on both sides. I think schedule 80 will help on flage hub stress but wonder if there is issue on leakage or installation.

Regards
STC

If it is possible it might rather be more prudent to use identical flanges, Sch 80,on both ends, and make the following butt joint tapered as per code allowed detail.

Perhaps one of the WN flange Sch 40 might have been integral with some equipment to lead you to the fix. if not so, you may consider the approach cited above.

Best regards

Venugopal

Thanks for your reply. I know the best way is to use the same schedule. However, we are not allowed to replace the mating existing flange with schedule 40, but we want to specify new flange with schedule 80 to match the new pipe section.

Regards
STC