Tapping of Blind flanges 1

[wagnermj]

I need to tap a 4" 300# RFBF with a 2.375" bore and prep the bore to allow for a full penetration weld for a 2" NPT diptube that will be installed through the flange. I have noticed that all of the "tapped" blind flanges that I have seen, have an extra portion of reinforcement on the opposite side of the sealing surface, built into the flange. I have seen blinds that come from the manufacturer with this extra reinforcement without a tap.

1. Does anyone know what the name of the blinds are called ?
2. Do these type of blind flanges need to be used when performing a tapping operation as listed above ?

I'll be grateful for any feedback, Thanks

 

[moltenmetal]

This is called a hubbed blind or reducing flange. The former are somewhat hard to find, but every SW reducing flange is made from one.