[Cricket]

I am looking for something like cleaning liquid to clean up the discoloration on stainless after welding. The places are tight and I cannot get there with the swab. Is there some kind of liquid and I can simply submerge the piece and it will clean up? The pieces are small about the size of a golfball.
However. I do not want to leave any agressive residues in the tight places. The same applies to the blasting and tumbling media. I do not want anything left in the piece. So preferably the stuff shall be easily wahsable.

I thought about a simple battery acid bath and a followup bath with backing soda to neutralize. May be you know better way?

[NYWELDERJim]

We make a lot of 304 and 316 stainless steel parts for semiconductor processing applications, most parts placed inside ultrahigh vacuum chambers. Cleanliness of the stainless surfaces is super critical. Every part we weld is run through an electropolishing process which uses a mixture of glycolic acid, sulfuric acid and deionized water at a temperature of 120 degrees F. The part is connected to a positive voltage source with the negative side of the DC power supply connected to a lead electrode. We adjust the current density for the part so there is a cleaning and surface polishing action. When the current density and polishing time are right, the parts come out beautiful!! We have an electropolishing tank which is about 100 gallons, for large parts we use a local outfit which can handle parts up to 12 ft. long. This process is pretty simple but something you need to have the proper safety precautions setup. I have setup small version ( 2 -5 gallons) of this system for processing lots of small parts. I have seen the same process offered using a portable swap which holds a small amount ofthe electropolishing solution for local cleaning.

Jim

[Otto Nobedder]

Jim,

That's very interesting!

I have to perform to "oxygen clean" quite regularly, and I have to say, the standards aren't as stringent as you describe. I may try to pick your brain on this in the future...

Steve S

[GreinTime]

Steve,

Do you guys use BlueGold cleaner at your employer? I thought I remembered my dad saying that that was what they used for a similar process, albeit he used it to remove all of the oil (and some of the color) from a pair of denim coveralls that he had

[Cricket]

Thanks Jim. It is interesting.
If the piece touches something does it leave an untreated spot?

[Oscar]

We make a lot of 304 and 316 stainless steel parts for semiconductor processing applications, most parts placed inside ultrahigh vacuum chambers. Cleanliness of the stainless surfaces is super critical. Every part we weld is run through an electropolishing process which uses a mixture of glycolic acid, sulfuric acid and deionized water at a temperature of 120 degrees F. The part is connected to a positive voltage source with the negative side of the DC power supply connected to a lead electrode. We adjust the current density for the part so there is a cleaning and surface polishing action. When the current density and polishing time are right, the parts come out beautiful!! We have an electropolishing tank which is about 100 gallons, for large parts we use a local outfit which can handle parts up to 12 ft. long. This process is pretty simple but something you need to have the proper safety precautions setup. I have setup small version ( 2 -5 gallons) of this system for processing lots of small parts. I have seen the same process offered using a portable swap which holds a small amount ofthe electropolishing solution for local cleaning.

Jim

Very good info. Are you allowed to go into details for this process as far as the actual mixture percentages are concerned, voltages, current draw?

[Cricket]

I found this:
Glycolic acid 55%, sulfuric acid 30%, water 15%

You need a current source(not the voltage source) and the current probably will be in 2-5A/sq.in. of treated surface. The piece connected to the positive pole. Electrode to the negative.

[Cricket]

Another source:
Currents start at 20 A/Dm sq, which translates to 185 A/sq ft.

The Metal Finishing Magazine Guidebook & Directory gives a number of solutions. A typical one is 15% sulfuric, 63% phosphoric, remainder water, used at 80 - 175 F and 50 A / sq ft.

[Otto Nobedder]

Steve,

Do you guys use BlueGold cleaner at your employer? I thought I remembered my dad saying that that was what they used for a similar process, albeit he used it to remove all of the oil (and some of the color) from a pair of denim coveralls that he had

Yeah, we use BlueGold in a hot tank for oxygen-clean.

I've never had the denim effect, but I don't think I've ever splashed it full-strength. In the hot tank it's 100:1 (for measuring simplicity, I mix it more like 85-90:1

I also use it cold at 50:1 if I need to clean the inside of a vessel. I'm VERY carefull about tracking anything into a vessel, as I hate the cleaning process. Even "lint-free" cloths leave textile fibers behind, and then these have to be cleaned up to something like 25/sq meter. I use nylon brushes for the scrubbing, but I still have to mop up the detergent, and then the rinse.

I'm also the only qualified inner vessel inspector on site, so when I blacklight it, I overdo it. (QCing your own work lives in two extremes... Some will say, "screw it, good enough." Some (like me) will nit-pick it to death.

Steve S

[GreinTime]

Yeah, but if you are the only one that can inspect, you are twofold the only one liable if it fails no? I mean I guess you could blame Steve the Welder, but then they might try and put you in the loony bin!

Seriously though, I don't think being overzealous on inspecting your own work on a rolling missile is such a bad thing!

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[Otto Nobedder]

Yeah, but if you are the only one that can inspect, you are twofold the only one liable if it fails no? I mean I guess you could blame Steve the Welder, but then they might try and put you in the loony bin!

Seriously though, I don't think being overzealous on inspecting your own work on a rolling missile is such a bad thing!

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Well, at least in my case "oxygen clean" only really applies to trailers in oxygen service. Our cheif client (you know who they are) does not switch "to" oxygen service, the trailers are dedicated, and only switched "out" of oxygen service.

I've done work for comanies, however, that WILL switch a notrogen or argon trailer to oxygen, and the stress level goes up.

A hydrogen service trailer will never be used for anything else, and while the oxygen protocols apply, the inspection can be a bit more relaxed.

I currently have an oxygen service trailer in "hold" mode for some engineering, as it has major inner-vessel cracks at front support locations.

Steve S

[GreinTime]

Ahhh I gotcha. And what does hold mode entail on the engineering end? Redo FEA to try and figure out a better solution as far as why it cracked in the first place? Or they just have to figure out a WPS for that specific job?

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[Otto Nobedder]

Ahhh I gotcha. And what does hold mode entail on the engineering end? Redo FEA to try and figure out a better solution as far as why it cracked in the first place? Or they just have to figure out a WPS for that specific job?

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In this case, it's a rare bird... A Cryenco made of steel, rather than aluminum. There's a fix, and there's documentation for the fix. It's just a matter of finding all the relavent drawings, specs, and EMOCs for the fix. The "root cause" must be fixed with/before the cracks in the vessel. The cracks are in the head, as well, which makes the fix all the more complicated. X-rays and R-stamp are one thing. A fix on the curvature of a vessel head are another...

I'll likely have the front of the outer vessel off entirely to fix the inner. I've only done this once before, and it's a complicated procedure, to be kind about it.

Steve S