Tapping a SS coupling on a keg

A few days ago, I posted a thread indicating a TIG welding job gone bad. The threads inside the coupling have been damaged and it's now impossible for me to screw on the 1/2" fitting like I had hoped to do. A trip to the hardware store looking for a 1/2" tap was not a success as the 1/2" tapping bit seems way to small to clean up the threads in my 1/2" coupling. I'm sure that there is something that I'm not catching. Does anybody know what size I should be looking for, exactly?

Thanks kindly!

marc

1/2" NPT (national pipe thread) tap is what you need.

Try non big box stores or order online. I know harbor freight and northerntool carry them.

What types of tools do you have available to you?

I am terrible at explaining things but try to picture this:

For male fittings:

Find a pair of dikes, or klines, (use for cutting metal) and pot them in the grooves towards the back of the fitting.

Squeeze with enough pressure like you were going to dent in but not crush a beer can (just checked it's perfect pressure).

keeping constant pressure turn counter-clockwise until you have gotten to the end.

For Female fittings:

A pice of welders tungsten is ideal but a small scratch awl will work and do the same.

also for female try threading a long bolt through the other end of the fitting.


For both:
heating with a torch first will help.



just remember: If it's already broke you don't need to worry about eFin it up!

Run the tap in just enough to clean the threads. NPT are tapered slightly to form an interference fit. If you run the tap in too far, the fitting will bottom before it gets tight.

I found out the hard way that stainless steel requires an anti-seize grease. When working with food you need to find a food grade version of anti-seize. I didn't have any so I used the next best thing "Crisco" shortening. Not sure about its ability to keep the stainless steel from galling, but it worked for me the one time I used it.

You will need to run tap into coupling about 3/4 length of the threads on tap to clean up the threads, as in previous post use "Crisco" or other vegetable oil for a lube on tap. When the tap reaches the point that it starts to cut the existing threads deeper it will get pretty hard to turn, usually a 1/2 turn past that point is deep enough.

I had this problem yesterday, I screwed a fitting into the coupling and used the wrench for a half turn and it ceased. and I messed up the fitting and coupling getting it out.

I bought some grease and just plan to boil and scrub them later.

I still notice that the fittings don't screw all the way in, is that normal?

A normal fit up is 3 turns by hand then approximately 2 by wrench for national pipe threads which are tapered. Watch out with stainless steel fittings, even a hand tight fitup can gall up and wreck the threads.

I read an article on galling, I believe that's the problem.

I can turn them in say three or four turns then maybe one revolution with a wrench.