Flange Alignment--Two Hole ?
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  1. #1
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    Flange Alignment--Two Hole ?

    I was at a friend's shop the other day and he was showing me two sections of pipe, about2 feet in diameter. They were welded at 90 degrees with a flange on the downward section. I was asking how do you verify that the top pipe and the bottom of the flange are parallel? He started to explain and got as far as "standard two hole...", and got interrupted. I never remembered to ask what that meant....So..what was he going to say??

    Thanks
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  2. #2
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    Re: Flange Alignment--Two Hole ?

    Well, when we do flanges at work, we assemble the piping system with two bolts and gaskets in the flanges, then tack everything together, then remove it (access is usually too difficult to weld in place), complete the welds, then reinstall with all of the bolts. The beautiful thing about flanges is that they usually have some slop in the fit so you account for all of the misalignment in your system in the welds on the flanges.

    Or else, you assemble with two bolts and gaskets, weld in place, replace gaskets as they have been burned in the welding process, then tighten with all bolts.

    Of course... when you're doing pre-fab none of this works.
    Last edited by 76GMC1500; 01-31-2012 at 01:10 AM.

  3. #3
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    Re: Flange Alignment--Two Hole ?

    I'm not sure of your description but when welding a flange to a pipe it can be either 1 or 2 hole.

    2 hole would have the top 2 holes level with each other. Usually bolts or flange pins are put in even #holes and a level laid on the pins.
    Leo

  4. #4
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    Re: Flange Alignment--Two Hole ?

    You install a level across two holes in the pipe flange.
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  5. #5
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    Re: Flange Alignment--Two Hole ?

    Leveling across two holes is only part of the procedure. You also need to make the flange faces square with the pipe in all directions. Adjustable pipe stands, a level and a square make this easier. They also make fancy chain fixtures to hold flanges but no one uses them.

    Dan

  6. #6
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    Re: Flange Alignment--Two Hole ?

    Quote Originally Posted by Dualie View Post
    You install a level across two holes in the pipe flange.
    Ding Ding Ding!!!

    That is how it was explained to me by the guy wanting pipe welded the first time.

    David
    Real world weldin.

    When I grow up I want to be a tig weldor.

  7. #7
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    Re: Flange Alignment--Two Hole ?

    TWO HOLE is the standard procedure because most valves, strainers, and devices attached to flanges are manufactured TWO hole. HOWEVER some import stuff can be one hole.There are flange line up pins that help, but usually a couple of oversize bolts that fit TIGHT in holes that are for fit up only and too large for installation purposes.

    http://pipefitter.com/existing_php/Matheyflups.php

  8. #8
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    Re: Flange Alignment--Two Hole ?

    Two hole set up
    Disclaimer; "I am just an a$$hole welder, don't take it personally ."

  9. #9
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    Re: Flange Alignment--Two Hole ?

    Okay, that makes sense, now! I got it and appreciate the words and pics. This large piece of work was made and used only one time. Then it was discarded, and I was told, probably going to be used to make a cooker. Lotta work and time and effort to be used just once.

    Thanks again for the explanation.
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  10. #10
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    Re: Flange Alignment--Two Hole ?

    Prints usually stipulate bolt holes to straddle centerline, aka the "two hole".

    It's a standard practice in the industry, stuff happens sometimes and somebody doesn't get the memo though.

  11. #11

    Re: Flange Alignment--Two Hole ?

    I have several nozzles on the top of a tank. they are all located radial from the centerline of the tank. Does two-holing apply per centerline, or is the 'vertical' centerline on the drawing of the tank assumed to be the two-holing line? I had a fabricator use the radial lines and claim it was the industry standard, but that sounds weird.

    Thanks, Jay

  12. #12

    Re: Flange Alignment--Two Hole ?

    been told that when two holing you get a more accurate reading on level if you place pins further apart.I have been a pipe fitter for 30 years and have never heard this until the other day.What do you think?

  13. #13
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    Re: Flange Alignment--Two Hole ?

    More accurate sure because you have a bigger average sample of horizontal to measure., but you can only two hole the flat face of a flange that way, not its mating flange, or the neck side of the flange because the pipe gets in the way. We used to use the next size up bolts, 3/4" in place of 5/8" bolts for two hole bolts. Just hammer them through a junk flange once, then back out, then the fit snug in the holes for a 5/8" bolt. Then just set a torpedo level across the top and you are two holed!
    When I was in a new job that used a lot of flanged fittings, the guy that I was working with asked "Do you know how to two hole?", I replied, "Yes I do, but my wife doesn't like it, so I don't try it very often." He was floored.

  14. #14
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    Re: Flange Alignment--Two Hole ?

    Thanks Walker.

    Reading your post, i got to the end and spat my coffee.

    Now i have to clean the monitor.
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  15. #15
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    Re: Flange Alignment--Two Hole ?

    I've been a pipe fitter and welder for 20 yrs.from the oil fields to paper mills. 2 hole is the standard practice on all flanges, If you have to EVER 1 hole or as some call it hole and half then someone has screwed up big time. 2 hole flanges is so no matter who or what makes up prefab pipeing then it will fit any flange of same size and weight class anywhere everytime. just my humble experience.
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