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4 inch pipe tap

Dave StromanDave Stroman Member Posts: 759
I have a100+ year old steam boiler that I am working on.  There is a 4" nipple in the bottom of the boiler that is rotted out.  I know when I crank on it with my wrench it will crush an collapse, requiring me to chisle out the threads.  The problem is getting my hands on a 4" pipe tap.  They cost $600 or more on line.  Crap!  I need to chase these threads and will probably never use it again. 

Any one have a trade secret on cleaning up these threads without a tap?
Dave Stroman


  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    Unless it is January and

    there was no other choice I would just have the people budget for a new boiler. If I had to do it I would tighten the nipple first then try and loosen it. If it collapses I would score it three times 1 inch apart as deep as I could without marring the female threads and fold it in. If the threads are dirty I use a rotary wire brush to clean the threads.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • heatpro02920heatpro02920 Member Posts: 991
    I have seen 4" taps for under $400

    But that is still a lot to pay, and you will probably never use it again...

    I have up to 2" but no 4" {could have fedexed it back and forth}...

    I would explain it to the customer, that they should be ready to install a new boiler but you are going to do your best..

    The good news is I have done this a couple times and 4" pipe is very easy because its so large, and since the pipe is rotted that is actually another plus.. I would first soak it in some home made penetrating fluid {acetone and tranny fluid} and then try to twist it out. If it collapses then get down there and file her out.. I use a nice sharp hacksaw blade with the skinny handle cut it before the threads and hammer and chesel it apart on itself... then a dremel tool with a steel brush to clean up the threads, teflon tape and pipe dope should get her done....

    I know customers hate to replace old boilers, especially large ones... But when you explain its going to be $1000 to replace that pipe they start thinking about it a little more seriously...

    Another note, I had a 2" pipe I did in a boiler that was over 40 years old, and it leaked with a steel nipple, even after chasing it with the tap and doping the heck out of it.... I tried a brass nipple in place of the steel nipple and it never leaked again...
  • hot rodhot rod Member Posts: 7,059

    If you just need to clean a thread take a hack saw and saw some slots into a 4" nipple, it turns it into a tread cleaner, but will not cut new threads.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Dave StromanDave Stroman Member Posts: 759
    Thanks for the advice

    Thanks guys.  If anyone knows where I can get a $400 4" pipe tap, let me know.  I will try it without, but need to keep my options open.
    Dave Stroman
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