Tapping in Blind Flange

I doubt that anything greater than 1" female pipe thread would be useful, and I bet that 1/2" fpt would be plenty.

Try with lesser to max diameter taps which decrease the machining(tapping) load which is easy for tapping more depth

I have seen sets of progressive taps used for this purpose. The first one taps in and bottoms....clean it out, next one and the final one that cuts to the bottom of the hole. I believe you need to clean often. A machinery handbook should deal with this. You may need a locknut, cotter or wire for securing it.

I prefer to use half coupling with NPS 1" socket welded or NPT (threaded) to be welded into the blind flange, and try to avoid threading directly into blind flange.

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Thanks to all for their valuable reply.

Actually we had tapped 1" hole in 1" blind flange, i know thats is quite unusual. Fuhrer we had used a BOSS for reinforcement (pls refer para 6.12.1 ASME B16.5 for reinforcement requirement of threads).

I was wondering if someone had the similar experience ?????

Thanks.