Cutting threads in stainless

[burlybeer]

I have a 1/2 stainless NPT fitting that I need to recut to a tapered NPTF to fit these tanks I have. I have the right tap and have tested it on a brass fitting with success but I am concerned about corrosion issues since the tap is not stainless. If I cut the threads and then passivate with nitric acid, will I be ok? What is typically used to cut threads in SS?

Thanks

Chris

[Moonlight]

I expect you will be just fine. The tap should be hard enough to remove the stainless yet not leave any bits of itself behind. As always, keep the tap well-oiled.
Yes, that is what is used to cut stainless threads.

[gitchegumee]

You should be fine. Hardened tool steel is nearly universally used to cut threads in stainless steel. That being said, the best (external) threads aren't cut, they're rolled. Most times threads wouldn't be tolerated on sanitary tanks except where an o-ring seals the sanitary space. Or on things like manway tighteners where a brass insert is used to keep the stainless shaft from galling against a stainless nut. And NPTF dryseal threads aren't made to be repeatedly dismantled and reassembled. Keep an eye on microbiological activity around the threads. Keep your tap oiled & good luck!