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  1. #1
    Join Date
    Mar 2010
    Posts
    10

    Default Determining Penetration Profile

    I am trying to determine which machine settings, gun travel, etc. will give me the best penetration on a T joint fillet weld between a 1/2" and 1/4" steel plate. I have welded a few coupons and cut them in half to view the penetration profile. The problem I have is that I cannot determine where the weld ends and the steel begins. Also, the parting line between the 1/2" vertical member and 1/4" horizontal piece disappears after it's been cut. Is there an inexpensive process to visualize these parameters? Dye penetrant? I am basically looking for something that will look like the pictures in some of the welding books I've been reading.

  2. #2
    Join Date
    Jun 2006
    Location
    Maine
    Posts
    732

    Default

    spray a little muriatic (HCL) acid on the saw cut... it will etch the steel so you can see the penetration...

    please use all standard precautions for hcl...
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  3. #3
    Join Date
    Nov 2008
    Location
    Atl, Ga
    Posts
    371

    Default

    The following procedure is how I etch my welds and will give you a "textbook" picture of how much penetration you're getting:
    -Bandsaw cut sample to a manageable size
    -Polish cut on belt sander or with 60 grit flap disc on an angle grinder. 60 grit is near bare minimum. Finer sandpaper grits/finishes will take more work, but give better contrast.
    -Submerge sample in tuppermare container of acid *etchant and let develop for about ten minutes
    -Remove and spray with ammonia base cleaner to neutralize acid (I use Windex)
    -Rinse with plain water
    -Dry sample

    *For my etchant I use Ferric Chloride printed circuit board etchant diluted about 50% with water ("PCB Etchant" from Radio Shack is Ferric Chloride). Diluted muriatic acid works too. There's a lot of recipes on the web - basically all are weak acids. Ferric chloride gives a nice grain contrast and is relatively easy to get, which is why I use it. It's neat to see each individual weld pass on a multi pass weld. If you want the sample to stay nice looking, give it a shot of semi-gloss clear lacquer or it will rust from humidity.

    CAUTION!
    Be safe always wear PPE, gloves and goggles. Also always remember to "add acid" when diluting. Adding water to a strong acid can cause it to boil rapidly and "explode". Working with acids can be dangerous - don't get stupid and don't get complacent.

    Not the best pic, but to give you an idea-
    Last edited by MR.57; 03-29-2010 at 07:07 AM. Reason: Pic added
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  4. #4
    Join Date
    Feb 2008
    Posts
    838

    Default

    The pictures in welding textbooks were prepared by machining flat, polishing to a mirror finish, cleaning with alcohol, and etching for a few minutes with nital etchant (2-6% nitric acid, balance methanol or ethanol). The surface is flushed with alcohol and photographed. It will rust in minutes, so to preserve the specimen, the etch area is oiled.

    In some instances, picral etchant (few percent picric acid in alcohol) is used. Depends on what metal is being welded. But for mild steel, the textbooks show a nital etch.

    Different acids selectively attack different components. Some metals are etched with ammonia solutions...

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  5. #5
    Join Date
    Mar 2010
    Posts
    10

    Default

    Thanks for all the info.

  6. #6
    Join Date
    Mar 2010
    Posts
    10

    Default

    Went out and tried to locate some of the chemicals recommended and had little luck. Best I could do was 1/2 gallon of muritic acid for etching concrete. Seemed like a waste to get 1/2 gallon when I'll only need a few tablespoons. On a whim, I decided to try a rust removal product I had sitting around in my garage called Picklex 20. I like this product for removing rust and keeping it off by providing a temporary barrier before painting. You can paint right over it and also use it as a weld primer. It etched the welds really nice. My camera was acting up, but I'll post pictures later. I have some questions on the profile and what concerns I may have.

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