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  • #16
    Originally posted by diamondback View Post
    there are calibration blocks that are "shot" to tell you what a specific thickness looks like. The reader then compares the thickness with the test specimen.

    There are different test blocks for the different densities of metals. It is fun to set up and run but reading them is a whole other skill set.
    Finally a difinative answer!I stand corrected Thanks for the information.
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    • #17
      Originally posted by 1428turbo View Post
      Finally a difinative answer!I stand corrected Thanks for the information.

      Every set of film has a built in gage, it's the pipe wall. Comparisons of deposit thickness are made against the parent metal (pipe wall).
      On an API production weld, concave stringers are generally acceptable as long as the weld deposit is as thick as the thinnest adjacent pipe wall.
      This stuff is easier to understand when you look at films.

      JTMcC.
      Some days you eat the bear. And some days the bear eats you.

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      • #18
        JTMcC,
        I agree that when you have an unburnt edge then you will have a well pronounced contrast difference, with good resolution. But it is still just a contrast difference.
        In addition to using an arrangement of different thickness shims for calibration, the same principle is used in profile radiography. RT can be used to shoot a side view of a pipe to show wall thickness. This is used typically when you have a line that is covered in insulation, or are unable to perform UT for thickness. A series of steel ***** (various sizes of ball bearings) that are made to very tight tolerances (microns) are set on the pipe and shot. From measuring the diameter of the ***** you can calculate the pipe thickness.
        "Religion is regarded by the common people as true, by the wise as false, and by the rulers as useful."

        -- Seneca the Younger

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        • #19
          JTMcC,
          We are doing some power house work. the pipe we are working on is 18" 2" thick. They are shooting each weld 3 times. You tig the root, run 7018 to fill up to 1/3 and shoot it. Put in another 1/3 of the filler and shoot it. Then fill it out and cap it and the final shot. They told us when we started one bad shot and you are out. Guess they have too many welders waiting in line.

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          • #20
            Originally posted by hogan View Post
            JTMcC,
            I agree that when you have an unburnt edge then you will have a well pronounced contrast difference, with good resolution. But it is still just a contrast difference.
            In addition to using an arrangement of different thickness shims for calibration, the same principle is used in profile radiography. RT can be used to shoot a side view of a pipe to show wall thickness. This is used typically when you have a line that is covered in insulation, or are unable to perform UT for thickness. A series of steel ***** (various sizes of ball bearings) that are made to very tight tolerances (microns) are set on the pipe and shot. From measuring the diameter of the ***** you can calculate the pipe thickness.

            Yea we are in agreement, I just want to point out that a shoulder that's not been broken down is much more well defined than say a concave stringer bead. And I think a low cap or concave stringer shows up pretty well.
            But I agree with what you say.
            To me, film shows a very clear (usually) view of what's actually there, IP/IPD seems very obvious to me.
            Like I said I've not viewed a million films, but in repairs and tie ins I've seen a few. It always shows a pretty clear image of what has happened in the weld.
            Even when the film reader can't tell you just how deep the indication is, it's usually somewhat apparant, ie wagon tracks are under the (not so) hot pass, bead defects are all the way in there, LOF or porosity or cold lap tells you (to a point) how deep it is by how far off the centerline it is, etc. Of course a indication on the centerline isn't much help.
            Usually the repair welder will see the defect as he searches for it. Sometimes not. In that case you can end up taking out everything, not so bad on .250W, pretty bad on 1.000W

            JTMcC.
            Some days you eat the bear. And some days the bear eats you.

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            • #21
              Originally posted by Finney View Post
              JTMcC,
              We are doing some power house work. the pipe we are working on is 18" 2" thick. They are shooting each weld 3 times. You tig the root, run 7018 to fill up to 1/3 and shoot it. Put in another 1/3 of the filler and shoot it. Then fill it out and cap it and the final shot. They told us when we started one bad shot and you are out. Guess they have too many welders waiting in line.

              On those steamer main steam leads that run 8" thick, high chrome, they shoot the weld every day. And of course weld on them for several days.

              It'd would be a pain to weld out a 8" wall pipe to discover a defect 1/2" from the ID

              JTMcC.
              Some days you eat the bear. And some days the bear eats you.

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