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Up Topic Welding Industry / Inspection & Qualification / AWS D1.6 Fillet Qualification
- - By CC4846 (*) Date 01-14-2020 17:48
Good morning,

      We need to qualify a fillet procedure per AWS D1.6. We are welding AISI 8622 Stainless to A36 with E312-16 SMAW electrodes. We need to perform macroetch tests. I have 30% Nitric acid and 10% Ammonium Persulfate, I tried both etchants on two sample welds and they both did nothing. I am looking for advice for a good etchant for this weld, and where I will be able to purchase the etchant.

Thanks for your help.
Parent - - By 803056 (*****) Date 01-14-2020 21:17
Superimpose a little voltage.

I use a 9 volt battery to apply some voltage to aid the acid etch operation. One terminal (-) to the piece and the other (+) to a piece of stainless sheet metal placed close to the area being etched.

Parent - - By CC4846 (*) Date 01-15-2020 19:29 Edited 01-15-2020 19:44
No kidding, does that really work? I did try it with no success, although the 9 volt battery did get pretty hot. I'm not sure that I understand the part about the sheet metal. I connected one battery lead to one side of the weld and the other lead to the opposite side of the weld so that the current passed through the welded area to complete the circuit. I tried again with both the nitric acid and the ammonium persulfate and I still didn't get any results.
Thanks again.
Parent - - By Lawrence (*****) Date 01-15-2020 20:16
Ive had some improved macros by going slightly cave man style...  With carbon steel.

Just warming the metal a little has produced some good results for me when using ammonium persulfate...

Not hot...  still warm enough to hold in a bare hand.. but just...  Maybe 140F or so.

No steam, no smoke, no increase in fumes...   But a little faster result and nice etch.
Parent - - By jwright650 (*****) Date 01-15-2020 20:46
Probably goes without saying but I'll say it anyway...the better the polish, the better the resolution of the etched surface
Parent - - By 803056 (*****) Date 01-15-2020 21:01
Cut, grind, polish (I like to get it to 1200 grit for the final), etch.

When you polish, use coarse, medium, fine, final with 1200 grit. With each successive finer grit, turn 90 degrees so you are polishing perpendicular to the last polish.

Connect the negative terminal to the piece of stainless and the positive terminal to the piece of sheet metal. Submerge in the acid. You should see bubbles coming off the stainless and moving toward the piece of sheet metal. You can move the sheet metal closer to the stainless piece to "speed" things up.

It only takes a brief time to etch. If held too long, it will blacken. Use a fine stainless brush to remove the smut. Immerse the pieces in the acid for a brief few seconds or so.

If it is in the acid too long, you may have to polish the sample again and start over.

Parent - By CC4846 (*) Date 01-16-2020 20:14
Ok , that makes sense now. I wasn’t submerging the part, just swabbing it with a Q-tip. Your scenario is similar to the old cathodic rust removal with a battery charger trick, I get it now. I don’t know how fine of a grit I have been polishing with. I sanded down with a flapper wheel then went to a brown Scotchbrite disc and finally finished with a blue Scotchbrite disk. It is not a mirror finish. I will get some polishing disks ordered. I also ordered some of this Stainless Steel Weld Etch online, I’ll give it a try when it arrives.
     Lawrence, I have also had luck with warming the part some when using ammonium persulfate on carbon steels. I have had just the opposite experience with the nitric acid though, I seem to get better results if the coupon is dead cold. I run cold water over it for in the sink a few minutes and it seems to have a better definition.
Thank you for your help guys!
Up Topic Welding Industry / Inspection & Qualification / AWS D1.6 Fillet Qualification

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