Etching welds
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Thread: Etching welds

  1. #1
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    Etching welds

    OK, I've searched the forum for quite a while for info on etching weld cross sections, remembering seeing somewhere what solutions to use...but just can't find the posts. Searched "etching", "penetration", "weld penetration", and some more.

    I cut and polished some sections of welds on 1/8" and 3/16" (T's, laps and butts) and want to etch them to check for penetration.

    First, there are no chem supply houses within 75 miles, so nitric acid is out. Pharmacies don't have it.

    Second, I tried muriatic (HCl) acid with poor results. I used dilute (10%) and full strength pool stuff (35%), both on cold steel and heated steel. I let the acid work for about 10 minutes and saw no action...no difference in the base metal and weldment.

    Third, I found some circuit board echtant at Radio Shack, but the stuff was about $10 for a small bottle and passed on that, not being sure if it would work ($$).

    Vinegar is only 5% acetic acid, so I wouldn't think it would be strong enough to show contrast.

    Any suggestions on what to use? Do LWS's normally carry something like that?

  2. #2
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    Re: Etching welds

    .



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  3. #3
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    Re: Etching welds

    Quote Originally Posted by DSW View Post
    DSW...thanks!! I had found the first one, but not the second one. Bookmarked that one for sure!

    I think my mistakes were (1) not heating the test piece and (2) not doing it enough times.

    Seems that it takes more than just one application, that being on warm steel. The second post you gave really cleared up the process for me. One good point he made was that you need to be quick to document the etching before it degrades. It also looks like he used acid straight from the bottle, which was one method I tried, but just not long enough.

    I also noticed the use of a heat gun. That would be a more controllable heat than using a propane torch or O/A.

  4. #4
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    Re: Etching welds

    I don't know what we use at school to test our welds, but it works instantly... I'll have to ask around.
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  5. #5
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    Re: Etching welds

    So I don't know anything about etching, but I get curious easily. I found this page on artistic etching, that included some info about chemicals:

    http://www.wikihow.com/Acid-Etch-Steel

    They made the interesting comment, to me, that using a chemical that forms an acid in water is typically a better choice than using an acid directly. For mild steel they recommended copper sulfate, with some table salt added to keep it from copper plating your sample. It will start out blue and turn colorless. It's used as an algacide, might find it at a pool chemicals place... It's also used for printmaking, etching printed circuit boards, etc., so it's probably available other places. It ships as a powder so it's easily available online.

  6. #6
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    Re: Etching welds

    Quote Originally Posted by keithwins View Post
    So I don't know anything about etching, but I get curious easily. I found this page on artistic etching, that included some info about chemicals:

    http://www.wikihow.com/Acid-Etch-Steel

    They made the interesting comment, to me, that using a chemical that forms an acid in water is typically a better choice than using an acid directly. For mild steel they recommended copper sulfate, with some table salt added to keep it from copper plating your sample. It will start out blue and turn colorless. It's used as an algacide, might find it at a pool chemicals place... It's also used for printmaking, etching printed circuit boards, etc., so it's probably available other places. It ships as a powder so it's easily available online.
    Interesting info. I'll have to check it out further if the HCl doesn't work well. Thanks.

  7. #7
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    Re: Etching welds

    I found exposure of a polished steel cross section to Naval Jelly (phosphoric acid) for about 5 minutes darkens the weld metal very nicely. See my avatar

    NJ is available cash OTC just about anywhere, no need to purchase nitric acid. If you really wanted some without raising eyebrows you could easily make it yourself from fertilizer and battery acid
    Last edited by wirehead; 11-22-2012 at 03:55 PM.
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  8. #8
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    Re: Etching welds

    Quote Originally Posted by wirehead View Post
    I found exposure of a polished steel cross section to Naval Jelly (phosphoric acid) for about 5 minutes darkens the weld metal very nicely. See my avatar

    NJ is available cash OTC just about anywhere, no need to purchase nitric acid. If you really wanted some without raising eyebrows you could easily make it yourself from fertilizer and battery acid
    Hey, I'll give the Naval Jelly a try. Planning a trip to the hardware store tomorrow and will get some. Thanks.

  9. #9
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    Re: Etching welds

    I used muriatic acid for etching. Left it in the acid for few hours until the pattern is visible.

    Tried to buy nitric acid but because it can be used to make explosives, its sale is controlled.
    Last edited by karu; 11-22-2012 at 06:34 PM.

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    Re: Etching welds

    Nitric acid is available here, but you have to have a company letterhead to document the sale.

    http://www.sciencecompany.com/Nitric...0ml-P6387.aspx
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  11. #11
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    Re: Etching welds

    Quote Originally Posted by wirehead View Post
    I found exposure of a polished steel cross section to Naval Jelly (phosphoric acid) for about 5 minutes darkens the weld metal very nicely. See my avatar
    Can you post a bigger picture of your avatar, or another example? I can't really see what's going on there, except for a couple very nicely laid beads...

  12. #12
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    Re: Etching welds

    I know you want etch your welds, but why? Are you having a problem with lack of fusion? I think doing some destructive testing might be less of a hassle and maybe more telling of issues.

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    Re: Etching welds

    Quote Originally Posted by Jay O View Post
    I know you want etch your welds, but why? Are you having a problem with lack of fusion? I think doing some destructive testing might be less of a hassle and maybe more telling of issues.
    I am not having a problem with a lack of fusion. Have you ever been just curious about something?

    A lot of welds look OK from the surface. Destructive testing basically tells you if the weld is sufficient and will hold up. I've done destructive testing but it does not give you a visual picture of the inside of the weld joint. I would like to see the depth of penetration, where the penetration is really going (like in a T-joint) or if there really IS any significant penetration.

  14. #14
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    Re: Etching welds

    If the welds look ok/good and pass DT there is no need to look further. How long have you been welding? I think the amount of depth of penetration is going to depend on your skill/experience. Usually more experienced welders will weld at hotter settings then newer welders resulting in more inter mixing of filler metal and parent metal. Maybe in etching you samples you should see about pushing your limits as a welder and do samples at different settings.

  15. #15
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    Re: Etching welds

    Quote Originally Posted by Jay O View Post
    If the welds look ok/good and pass DT there is no need to look further. How long have you been welding? I think the amount of depth of penetration is going to depend on your skill/experience. Usually more experienced welders will weld at hotter settings then newer welders resulting in more inter mixing of filler metal and parent metal. Maybe in etching you samples you should see about pushing your limits as a welder and do samples at different settings.
    If you will go back and read my OP, it had nothing to do with destructive testing, rods, current settings or experience or anything else except: what to use for etching in order to see the cross section of a weld....

    What would YOU use if you did etching on a weld section? Some others have posted some really good suggestions and I'm trying them all to find the best.

  16. #16
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    Re: Etching welds

    Quote Originally Posted by Jay O
    If the welds look ok/good and pass DT there is no need to look further.
    I disagree. Different analysis techniques reveal different potential "defects". Different jobs have different requirements.

    By way of example, I encountered early in school short tracks of very minute pinholes INSIDE my welds of this type. These would never would have been revealed using, say, a bender or simple BFH test (the bender in school had been "bent" by somebody who is not me so I couldn't have used that method anyway). These "defects" would have been obvious to an xray (our "test"). So practice, weld, cut, etch, analyse, practice, ..., practice. Since making cert plates was no small amount of hard hot work out here, I wanted to be sure my plate was as good as I could possibly produce, both externally AND internally, before being xrayed. I passed.

    Keith, you're in luck, I just happen to have saved the original photo I used for my avatar.



    You can get some idea of degree of "penetration" over four passes from root toward, especially, the cap at the boundaries of the original V-groove. I never took pictures of my other "etchings" and this was my last 3G attempt before my "test"
    Last edited by wirehead; 11-23-2012 at 05:22 PM.
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  17. #17
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    Re: Etching welds

    For what you're trying to do, the dilute muriatic acid is probably the best thing available. it's going to take a while to get some results you can see with the naked eye at room temperature.

    You won't see much unless you've really done an excellent job polishing first. You need to polish the surface to be etched with at least 800 grit; which means using 120,.240, 400, and 600 grits first to progressively remove scratches. For better detail, you need to wet polish with even finer grit. 1000, or up to 2000 grit with water will produce a good mirror polish that etching can show lots of details on.

    Best technique I know for this on the cheap is to use a sheet of window glass as a flat surface to place your abrasive on, and then use running water while rubbing your weld on the abrasive sheet. The glass will give you a very flat surface to work on. Use light pressure and go in a single direction until all the scratches are in the same direction. Wash your weld in clean water, change to a finer grit, and repeat. Turn the weld 90° each time you move to a finer grit, and polish until the scratches in the previous direction are all gone. If you carry grit from a coarse sheet to the finer sheet you'll just put more scratches into the weld surface than you can remove.

    If you're going to look at these welds under a microscope, then you need to go even further, using expensive diamond pastes and ultra fine silica as a polishing media. The most sophisticated etching processes use all of these, and then electro-polish the sample.

    This website has a good reference page on etchants and metallography techniques.

    http://www.metallographic.com/Etchants/Etchants.htm

    Most of what they recommend is beyond the budget for the average person and is only available to universities, specialized labs, and big companies.

    The one thing you could do beyond more polishing is to etch using boiling HCL acid solution. But this is very dangerous, as the fumes created are very toxic. Unless you've got access to a fume hood and proper safety gear, I don't recommend you try this. I've seen this done on forged parts to look for macro - defects, and it works well. It's much faster than room temperature etching. But it's not safe, even with the best gear.
    Last edited by A_DAB_will_do; 11-23-2012 at 05:25 PM.
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  18. #18
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    Re: Etching welds

    Quote Originally Posted by wirehead View Post
    I disagree. Different analysis techniques reveal different potential "defects". Different jobs have different requirements.

    By way of example, I encountered early in school short tracks of very minute pinholes INSIDE my welds of this type. These would never would have been revealed using, say, a bender or simple BFH test (the bender in school had been "bent" by somebody who is not me so I couldn't have used that method anyway). These "defects" would have been obvious to an xray (our "test"). So practice, weld, cut, etch, analyse, practice, ..., practice. Since making cert plates was no small amount of hard hot work out here, I wanted to be sure my plate was as good as I could possibly produce, both externally AND internally, before being xrayed. I passed.

    Keith, you're in luck, I just happen to have saved the original photo I used for my avatar.



    You can get some idea of degree of "penetration" over four passes from root toward, especially, the cap at the boundaries of the original V-groove. I never took pictures of my other "etchings" and this was my last 3G attempt before my "test"
    How did you find those very minute pinholes? You found them by doing some DT as you state "practice, weld, cut, etch, analyse, practice..." You found thoughs discontinuities and worked on your technique to improve. I'm just saying that the etching part isn't neccessary and alot is still learned without it. If someone does ok/good looking welds that pass VT along with sound technique and continually pass DT, they will have a very high chance of passing RT.

  19. #19
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    Re: Etching welds

    Quote Originally Posted by Jay O View Post
    How did you find those very minute pinholes? You found them by doing some DT as you state "practice, weld, cut, etch, analyse, practice..." You found thoughs discontinuities and worked on your technique to improve. I'm just saying that the etching part isn't neccessary and alot is still learned without it. If someone does ok/good looking welds that pass VT along with sound technique and continually pass DT, they will have a very high chance of passing RT.
    JayO...I really don't think you are getting the message here. It's not IF ETCHING IS NECESSARY...it just happens to be (1) another tool to improve anyone's welding technique and most importantly (2) it just happens to be something I want to try. You having a problem with that???

    Gad...this is turning out to be as bad as a frickin' trailer welding thread

    "A_DAB_will do" and "wirehead"...(and others) thanks for the constructive comments and suggestions

    So far, I think the best advise other than the type of etchant is to polish better and let the etchant soak longer.

    I THINK I'M DONE WITH THIS THREAD!! Thanks to all for your constructive advise. Gonna start etchin' some stuff.

  20. #20
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    Re: Etching welds

    Post up how things work for you along with some picts.
    .



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  21. #21
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    Re: Etching welds

    Quote Originally Posted by DSW View Post
    Post up how things work for you along with some picts.
    Will do...

  22. #22
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    Re: Etching welds

    In the UK you can Buy Nitric acid, theres some for sale on ebay, not sure of the US, so check there,

    as described you need to polish up the cut test piece as best you can and then apply a small blob of the acid, which has been diluted 10% acid to 90% water

    Wait a few minutes and then you'll see the fusion/penetration, heres some i did earlier
    Attached Images Attached Images     


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    Re: Etching welds

    Taken from API 1104 code book.

    "For each macro-section test specimen, at least one face should be ground to at least a 600 grit finish and etched with a suitable etchant, such as ammonium persulfate or dilute hydrochloric acid, to give a clear definition of the weld structure. "

    Hope this helps.

  24. #24
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    Re: Etching welds

    This etching process is only noted in Appendix B-In-Service welding on live pipelines. In all other sections of the code states VT, DT, RT, and UT.

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    Re: Etching welds

    Quote Originally Posted by Jay O View Post
    Taken from API 1104 code book.

    "For each macro-section test specimen, at least one face should be ground to at least a 600 grit finish and etched with a suitable etchant, such as ammonium persulfate or dilute hydrochloric acid, to give a clear definition of the weld structure. "

    Hope this helps.
    It does, thanks.

    As others have pointed out as well, the polish needs to go further than I have carried it. I just buffed down to 400 grit. I'll go with finer grits. Also, I believe a bit of heat will help. The shop is in the 30's and 40's and, of course, acid reacts much better when warm. Will get out the heat gun or propane torch. One poster had a pic of a heat gun, which should be easier to control.

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