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Thread: Etching welds

  1. #51
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    Re: Etching welds

    This was posted on the aws forum a long time ago by Richard M. Beldyk.
    Gives some opinions on the process as well as suitable acids.


    GUIDELINE FOR ETCHING LOW-ALLOY STEEL

    1. Scope

    This document is an in-house guideline for both MICRO and MACRO Etching steel samples.

    2. Purpose

    The AWS Structural Steel and Bridge Welding Codes, AWS D1.1 and D1.5, respectfully, specifies that MacroEtching of weld samples is required for procedure and welder qualifications, yet does not provide details on how to complete these tests. This guideline fills the void that exists between the codes and practical applications of them with respect to "MacroEtching."

    3. Procedure

    Specimen Surfaces preparation

    Care must be taken to prevent overheating the specimen during polishing. Excessive pressure during polishing will form deep scratches and will increase the depth of disturbed metal on the surface of the specimen.

    Rough polishing

    This operation can be performed by means of different type sand paper. For rough polishing, a adhesive sand paper should be used as a covering for the rotating polishing wheels. During rough polishing the specimen is moved in a clockwise direction around the polishing wheel to insure equal metal removal from the entire surface by not allowing prolonged polishing in any one direction.

    Fine Polishing

    Fine polishing is often done using a water coolant and silicon carbide abrasive paper mounted on a rotating disc. The two-wheel unit in the laboratory can be equipped with rough polishing wheel and a final polishing wheel. Wheel speed for final polishing has to be set at a second position (about 1150 rpm). A small stream of water is directed at the center of the rotating wheel.


    Final Polishing

    Final polishing is very similar to that used for rough polishing. Aluminum oxide is the most popular final polishing abrasive for ferrous and non-ferrous materials. It is also possible to use chromium oxides for soft materials.

    The abrasive particles used in final polishing are generally carried on a napped or short pile cloth such as billiard cloth or "microcloth." Most polishing cloths can be obtained cut to size and coated with an adhesive backing. The adhesive back eliminates the need for mechanical clamping.

    CAUTION!
    Be sure that you supply the rotating wheel with continuous flowing water. This step is taken to insure cool surface during polishing.

    Etching of specimens

    Temperature - 160 to 180 F.

    Polished metal specimens usually show no structural characteristics. Etching of the metal surface is done to make visible the crystalline structure of the metal and to produce optical contrast between the various constituents. Etching is done by exposing the cleaned and polished specimen surface to suitable etching solution such as those described in Table 1. These etching reagents are powerful, hazard and must be handled with care.

    CAUTION!
    Do not forget: etchants are composed of organic and inorganic acids, alkalis or other complex substances.


    If the specimen is not sufficiently etched after the first application the etching process may be repeated.

    If the specimen is overetched it must be repolished prior to re-etching. Immediately following the etching the specimen should be washed in warm water to stop the etching, then immersed in alcohol and finally dried in a blast of warm air. Rapid drying is important to prevent water spots.

    Etching reveals structural characteristics by preferential etching. That means that some areas such as grain boundaries are more highly stressed than other areas and are more subject to chemical etching.


    Table 1
    Carbon and Low-Alloy Steel Etchants

    ETCHANT COMPOSITION TIME CHARACTERISTICS REVEALED

    Nital 1-5% Nitric Acid95%-99% Methanol 5-30 minutes Macroscopic examination - Carburization and decarburization, hardness penetration, cracks, segregation, weldd examination.- Average ground or polished surface.Microscopic Examination - Develops ferrite grain boundaries in low-carbon steel; produces maximum contrast between pearlite and a cementite or ferrite network; develop grain boundaries in 4% silicon steel; develops ferrite boundaries in structures consisting of martensite and ferrite; etches chromium-bearing low-alloy steels resistant to action of picral. Darkens pearlite. Polished surface.

    Picral 4 gram Picric Acid100 ml Methanol 3 - 5 hours Carbon and Low-Alloy Steels. Macroscopic examination - Carbon SegregationMicroscopic Examination - Reveal s maximum detail in pearlite, untempered and tempered martensite, and bainite; reveals undissolved carbide particles in martensite; differentiates ferrite, martensite, and massive carbide by coloration; differentiates bainite and fine pearlite; reveals carbide particles in grain boundaries of low-carbon steel and wrought iron - Polished surface.

    Iodine Tincture, USP 15 to 60 minutes Macroscopic Examination - works better with steel is 180 to 200 F. Slow but available from Pharmacy

    1 part HCL Hydrochorlic Acid (Muriatic Acid) - 1 part Distilled Water 15 to 60 minutes Macroscopic Examination - Segregation, porosity, hardness penetration, cracks, inclusions, dendrites, flow lines, soft spots, structures, weld examination. - Sa-cut, machined or average ground surface.



    4. Acceptance

    For acceptable qualification, the test specimen, when inspected visually, shall conform to the following requirements:
    Fillet Welds. Fillet welds shall have the following:
    1. No cracks
    2. Thorough fusion between adjacent layers of weld metals and between weld metal and base metal
    3. Weld profiles conforming to intended detail, but with none of the variations prohibited in AWS D1.5 3.6
    4. No undercut exceeding 1 mm.
    5. Fusion to the root of the joint but not necessarily beyond.
    6. Leg sizes equal to or greater than the specified leg size.

    5. Principal MacroEtch Observations to be Recorded

    Identification to use on Photograph Description Location
    A Cracks Surface or Subsurface
    B Seams or Laps Surface or Subsurface
    C Decarburization Surface or Subsurface
    D Pinhole Surface or Subsurface
    E Segregations Surface or Subsurface
    a Pipe Center or Central Area
    b Porosity Center or Central Area
    c Bursts Center or Central Area
    d Segregations Center or Central Area
    " Flakes or Cooling Cracks General
    $ Dendritic Pattern General
    ( Ingot Pattern General
    * Grain Boundaries General


    6. Reporting Requirements

    A digital photograph shall be taken of the macro/micro etched specimen for inclusion in any report or PQR. Indications on the photograph shall be marked as listed above.

  2. #52
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    Re: Etching welds

    Here is one I did. This is aluminum, I cut and polished. Then I warmed the metal up and used easy-off oven cleaner










    Sent from my iPhone using Tapatalk Pro

  3. #53
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    Re: Etching welds

    That's some nice penetration Dave. Did u use a helium mix?

  4. #54
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    Re: Etching welds

    The oven cleaner makes a pretty good mess

  5. #55
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    Re: Etching welds

    No helium mix on that. In fact that's using my HTP propulse 200 mig machine.

    As far as the mess goes, what I should have done, and now do in the future, is I spray the oven cleaner into a little cup and use a q-tip swab spread on the weld.




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  6. #56
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    Re: Etching welds

    Nice. I can tell that's good penetration. That's a good idea. I usually try and shield with a rag and not get to trigger happy like u got lol

  7. #57
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    Re: Etching welds

    Nice. I can tell that's good penetration. That's a good idea. I usually try and shield with a rag and not get to trigger happy like u got lol

  8. #58
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    Re: Etching welds

    Thank you for posting that Pete.S. that is a lot of information to absorb. I think I will have to read it several times for all of it to sink in.

    Quote Originally Posted by motolife313 View Post
    Looks Like u got well passed the root. Nice job. Now how about some aluminum?
    Sure send some Aluminum my way, I'll run all the tests you want

    Quote Originally Posted by shortfuse View Post
    Yes, I got a successful etch from a polished weld. No pictures though. Used Naval Jelly. The etch was faint but clearly outlined the penetration. I need to get some more concentrated phosphoric acid, but it would be a thousand years before I used one of the pint or gallon jugs!!!!!
    Pics or it never happened :P

    Nice pen Smartdave. Looks like oven cleaner works good on Aluminum thank you for sharing.


    Last nite I ran more beads at different wfs and was experiencing what I think was arc blow. The wire was wondering. I have seen this a couple times now. First few times I saw this I thought I was experiencing feeding issues but now I think it is arc blow. I also experienced a lot of porosity in the puddle when this was happening. The 1/2" plate I am Welding on is magnetised from welding and I think this is part to blame for the arc blow.

    CEP thank you for all the info and links you shared
    Last edited by N2 Welding; 05-17-2017 at 11:48 AM.
    Lincoln, ESAB, Thermal Dynamics, Victor, Miller, Dewalt, Makita, Kalamzoo. Hand tools, power tools, welding and cutting tools.

  9. #59
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    Re: Etching welds

    a little late to the party, I understand but jody - welding tips and tricks - does this lots on his youtube channel. Tells you all about it

  10. #60
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    Re: Etching welds

    I tried the lock tight naval jelly recommended by Jody with no luck. I will try it again using more than a thin coat and let it sit for at least 5 minutes. I am just too impatient to wait 5 min. What sucks about this is the buffing wheels are not cheap just for testing but when I think about it compared to having a weld fail The testing is cheap.
    Last edited by N2 Welding; 05-17-2017 at 10:51 AM.
    Lincoln, ESAB, Thermal Dynamics, Victor, Miller, Dewalt, Makita, Kalamzoo. Hand tools, power tools, welding and cutting tools.

  11. #61
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    Re: Etching welds

    tag - etching
    "Where's Stick man????????" - 7A749
    "SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55
    "I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding
    "Stick-man"

  12. #62
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    Re: Etching welds

    Hey CEP are you using the phosphoric acid full strength or are you diluting it with another liquid?
    Lincoln, ESAB, Thermal Dynamics, Victor, Miller, Dewalt, Makita, Kalamzoo. Hand tools, power tools, welding and cutting tools.

  13. #63
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    Re: Etching welds

    Right out of the bottle. Just use a small paint brush. The little foam ones work good.
    Dont pay any attention to me
    Im just a hobbyist!

    Carl

    Dynasty 300
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  14. #64
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    Re: Etching welds

    Quote Originally Posted by CEP View Post
    Right out of the bottle. Just use a small paint brush. The little foam ones work good.
    Thank you turns out the reagent you linked is only sold to schools and businesses. It looks like I can get the technical grade on ebay no problem.
    Lincoln, ESAB, Thermal Dynamics, Victor, Miller, Dewalt, Makita, Kalamzoo. Hand tools, power tools, welding and cutting tools.

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