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Thread: unscrewing metal dwv pipe (is it impossible?)

  1. #1
    DIY Member adrianmariano's Avatar
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    Default unscrewing metal dwv pipe (is it impossible?)

    I'm trying to unscrew a 1.5 inch metal drain pipe because the new pipe needs to be shorter to connect to the new sink. (Existing pipe is also about 50% blocked with crud as well.) I've pushed at it with my 14" pipe wrench, I've sprayed it with WD-40 and liquid wrench, and I've heated the fitting a bit with a torch. I can't get the pipe to budge. It did look rusted at the joint.

    Is there hope to get this unscrewed? If so, how?

    Or should I give up on getting this unscrewed and instead cut it short and use a banded coupler? The pipe has a rough coat of paint on it so I assume a banded coupler will require removing the paint to get a good seal?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    A bigger wrench! Problem is, if the vertical pipe is obstructed by that much, the rest of it might be worse. Maybe replacing more of it is in order. Wait for one of the pros' ideas.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Plumber plumber1's Avatar
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    Big wrench and try tightening, you might be surprised.

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    In the Trades kordts's Avatar
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    If you can bang on the hub with a hammer, you will get it loose. Keep banging around in a circular fashion.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by kordts
    Keep banging around in a circular fashion.
    ... while applying plenty of torque with a big wrench!

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    DIY Senior Member TedL's Avatar
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    A 3 foot length of pipe slipped over the handle might work as the "bigger wrench".

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    Plumber Cass's Avatar
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    Heat the fitting real good and it will come out. As hot as you can get it. Use map gas if you can.

  8. #8

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    PB blaster is better than either of those....spray it on....tap around the fitting...use a cheater bar for leverage....if it still won't break free...try tightening, then loosening....if that don't work....cuss, stomp around.....and then do like Cass said and break out the torch....just make sure you have a spray bottle of water handy..

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    Plumber Cass's Avatar
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    While PB blaster is great and the best on the market, in my NSHO, if the threads were doped I doubt it will penetrate the old dope but hey, the Patriots lost...anything is possible.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default pipe

    Few things are impossible, but since this is under a sink it could be, or at least very difficult. Do not tap on the hub very hard or you might crack it and then you WILL have to replace it. Use the biggest wrench you can get into the cabinet, and hit on the end of it fairly, or very, hard.

  11. #11
    Plumbing Contractor srdenny's Avatar
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    Cut the riser, clean the line, put on a Mission CP150 coupling and you're ready to go.

  12. #12
    DIY Member adrianmariano's Avatar
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    Thanks for all the suggestions.

    This is not a kitchen sink, but rather a utility sink, and right now there's no sink at all, so I'm not trying to work in a tight space. The only limitation I have is that I'm about 2" away from the cinderblock foundation wall and about 6" above the concrete floor.

    The pipe that I'm trying to remove, which is ~50% blocked, is horizontal. I hope that the vertical pipe it connects to is in better shape in terms of blockage. (The kitchen sink is the other thing on the same drain line (right above) and it drains at a reasonable speed. I've always thought the old utility sink was rather slow to drain.) I believe the vertical pipe is vented out the roof.

    Turns out I've been using PB Blaster, not liquid wrench. I think when I went to buy liquid wrench they sold me the PB blaster instead.

    Just how hot should I try to get the fitting? I already caught the paint (on the pipes and wall) on fire trying to heat it up with my mapp gas torch, and it hasn't moved. I mean, should I be trying to get it to start glowing? Am I risking cracking the fitting? Do I put the pipe wrench on while the fitting is still hot? (And what's the sprayer for?)

    Regarding a longer wrench, I am of course using the longest wrench I have on hand. I did a quick check of what they're selling at Home Depot and a 24" pipe wrench is pretty costly. Does it make sense to spring for the two foot pipe wrench or is the length of pipe on the handle likely to work about as well? (I only have plastic pipe on hand so one way or the other I gotta buy something.) I could get a longer pipe than pipe wrench.
    Last edited by adrianmariano; 01-22-2007 at 05:52 AM.

  13. #13

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    Quote Originally Posted by Cass
    While PB blaster is great and the best on the market, in my NSHO, if the threads were doped I doubt it will penetrate the old dope but hey, the Patriots lost...anything is possible.
    ....I guess I could just skip that and go straight into cuss/stomp around then.....actually I get a long enough cheater bar and I will break "something" loose......

  14. #14
    DIY Senior Member TedL's Avatar
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    The way HD prices black pipe, I'd buy a full 10' length of 1 inch and have them cut and thread a 2', a 3' and a 5'..you pay the single full length price.

    Pry bars like this also come in handy when you're doing the FWD axles on a car. 3/4 pipe may also slip over your wrench handle, but the price diff.....your call.

  15. #15
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by adrianmariano
    I only have plastic pipe on hand so one way or the other I gotta buy something.
    I have used 1-1/2" sch40 pvc to extend handles. That stuff is pretty tough. Also, I would be cautious about a lot of heat. Rather, a few cycles of heat-it-a-bit-and-let-it-cool might help a little better. Fire wrenches are great, but they can also be counterproductive! And since your pipe is horizontal, you might either have someone stand on the handle or maybe you can set up some leverage off the floor.

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