Keggles & Welding/Cutting "Slag" Cleanup

[revco]

Hey all,

I don't know if I just got the short straw or what, but I received my kegs (now keggles) back from the welder today and the insides were covered in a brown, "slag" type material. It's almost like a spray of rough, brown, hard material that's stuck to nearly all sides of the keggles. I'm guessing it was a byproduct of the grinding or plasma cutting, whichever method was used. (I suspect a grinder.) I wasn't there for the process, so I don't know precisely what happened, but I haven't read anything about this.

I've spent the last hour+ scrubbing them down with bar keep's friend and a Scotchguard pad. I mean really going to town. For the most part, they're clean...but there's still residual "slag" left over that's proving difficult to remove. I'm reluctant to take steel wool to the inside of my brand new keggles. I'm sure it would do the trick, but I fear scratching the insides up of these (now) $300+ keggles something fierce. (Steel on steel = same hardness = scratch possibility)

Got a couple questions:

1. Is this normal? I wasn't expecting this condition. Should I be concerned? These are for a HLT and BK, respectively.
2. What would you recommend for thoroughly cleaning it off? Steel wool and barkeep's friend? A long, long double soak in oxy? What do you think?

I tried searching for my answer, which is how I usually roll, but the search failed me with everything I could think of. I don't ask many questions, but when I do, it means I'm really in need of an answer.

Thanks a million for all I've learned here!

 

[SpikeBrewing]

Hey all,

I don't know if I just got the short straw or what, but I received my kegs (now keggles) back from the welder today and the insides were covered in a brown, "slag" type material. It's almost like a spray of rough, brown, hard material that's stuck to nearly all sides of the keggles. I'm guessing it was a byproduct of the grinding or plasma cutting, whichever method was used. (I suspect a grinder.) I wasn't there for the process, so I don't know precisely what happened, but I haven't read anything about this.

I've spent the last hour+ scrubbing them down with bar keep's friend and a Scotchguard pad. I mean really going to town. For the most part, they're clean...but there's still residual "slag" left over that's proving difficult to remove. I'm reluctant to take steel wool to the inside of my brand new keggles. I'm sure it would do the trick, but I fear scratching the insides up of these (now) $300+ keggles something fierce. (Steel on steel = same hardness = scratch possibility)

Got a couple questions:

1. Is this normal? I wasn't expecting this condition. Should I be concerned? These are for a HLT and BK, respectively.
2. What would you recommend for thoroughly cleaning it off? Steel wool and barkeep's friend? A long, long double soak in oxy? What do you think?

I tried searching for my answer, which is how I usually roll, but the search failed me with everything I could think of. I don't ask many questions, but when I do, it means I'm really in need of an answer.

Thanks a million for all I've learned here!

***FIRST, DO NOT USE STEEL WOOL***

The iron in steel wool will impregnate the stainless steel keg and cause it to rust. Never use anything iron to clean a stainless piece. Also don't use a wire brush that has been used on steel because it can have the same affect.

What you're looking at is slag from when the welder cut them open with a plasma cutter. This stuff is an absolute ***** to get off (which you've found out). I used to cut kegs open with a plasma cutter but stopped due to the slag. I never found an easy way to get it off however. I used to use hot soapy water and A LOT of elbow grease.

I would recommend doing a boil in the keggle and then scrubbing it again. Hopefully someone chimes in that found the trick to getting rid of this.

 

[bad67z]

I have used a plasma cutter to cut open a number of stainless vessels. The dross (slag) left behind can be a bit challenging but is easily taken care of.

You can usually take another piece of stainless or mild steel (depending on the base material), slide it across the surface striking the dross on the back side.

I found this sales video, while I find it a cool tool you can to the same thing with a piece of flat sharpened scrap.



The difficulty with a keg is getting the correct angle since the material your attempting to remove is inside the lip. I can usually get the majority off by scraping, but I do the real finish work with a 4 1/2" aluminum oxide flap disk and my trusty grinder.

 

[revco]

Interesting. Thanks for the tips so far. I'm thinking that a grinder may be slightly dangerous to exposing rust risks on the stainless. Now that I know what this is (plasma cut slag), I was able to find more relevant search results.

I realize now I should have asked them to fill the kegs with water when cutting. Word to the wise!

I found a couple posts of the same thing:

https://www.homebrewtalk.com/f11/rust-spots-new-keggle-312132/index3.html

This person reported they were able to successfully use undiluted Starsan to get the slag off. (He says it was rust, but it looks like slag to me.)

https://www.homebrewtalk.com/f51/cleaning-plasma-cut-keggle-ideas-240926/

Here, BobbyM mentions using GatorGrit fine pads. May be more abrasive than what I want. A flap disc, as mentioned above, may also do the trick. Worst case, using a stainless chisel of some sort will force it off with shear brute force...but this may be tricky in some of the locations.

Is an aluminum oxide flap disc safe on the inside of a keggle? I know aluminum is a soft metal, so it should be OK, but I don't want these things to rust. Ever.

I think I'll try the methods discovered in order of least aggressive to most aggressive until they're as clean as I want.

Thanks all!

 

[dmfa200]

As long as you use a new grinding/sanding disk your equipment will be fine.
Don't use a chisel. If you can get your hands on a small piece of stainless plate you could make a scraper and use that.
I doubt you will remove every bit of it without resorting to a sanding disk.
Don't worry about damaging your kegs. Just use new abrasives.
I've been welding and working with stainless for the last 15 years in chemical plants and aerospace to various codes, if you have any doubts about my advice.

 

[Breck09]

I am having this same problem. I used steel wool though before finding out that I shouldn't. Is there any way to make sure I get it cleaned up so I don't have rust problem? Still trying to find out a way to get the slag off as well.

 

[SpikeBrewing]

I am having this same problem. I used steel wool though before finding out that I shouldn't. Is there any way to make sure I get it cleaned up so I don't have rust problem? Still trying to find out a way to get the slag off as well.

Since you used steel wool it may rust but it'll only be surface rust. Wiping it away with your finger will get rid of it. Bar Keepers Friend will be your best friend if you see any surface rust pop up.

 

[Breck09]

Since you used steel wool it may rust but it'll only be surface rust. Wiping it away with your finger will get rid of it. Bar Keepers Friend will be your best friend if you see any surface rust pop up.

That is good to know. When I was using the steel wool I thought in the back of my head I probably shouldn't be doing this but that slag was still pissing me off. Going to try the BKF paste to get it off. I guess if worse come to worse I read a sander could work. I don't have access to an angle grinder.

 

[sapper-nc]

If you have a small angle grinder or even a dremel tool or drill, you can find the gator grit style disc's (fiber material not metal) or sandpaper like discs at lowes , home depot has some but they have a different name. Its definitely fixable .. pop a couple beers and wear some gloves and goggles

 

[fork]

Chipping it off with another piece of stainless is a good idea. Also for the person who used steel wool, barkeepers friend or a bath in citric acid will dissolve the free iron the became imbbeded or exposed on the surface of the stainless. Be careful if you go the citric acid route though.

 

[revco]

OK, well I think we can safely scratch undiluted StarSan off the list. I didn't let it sit, but it did very little to the slag. What little it did do, I attribute to serious roughing with the pad.

I don't mind taking my angle grinder to the inside, but want to make sure I get the right pads. I'll try to find the fibered gator grit pads because that sounds preferable...like a Scotchguard pad, just running at 10,000 RPM. :rockin: Should I use a polishing compound with this at all?

If I'm forced into an aluminum oxide flap disc, what grit would you recommend? 60 grit appears to be a pretty common size but that seems a bit on the rough side to me? I really would rather not have a scratched up inside.

Breck - just as an FYI, I went to town with BKF and a scotchguard pad and was still having difficulty getting the more difficult slag off. It might be possible with hours and hours of tough labor, but I'm trying to avoid that. You might find yourself in the same boat as me.

 

[SpikeBrewing]

I used 40 grit aluminum oxide to do a rough clean up on top after I cut them off. The are really abrasive and will leave the inside of your kettle looking very rough. After a pass with the 40 grit aluminum oxide disc I used a 150 grit flap disc to get a smooth finish. For what you need I would recommend nothing rougher than a 220 grit.

 

[revco]

Perfect. That's along the lines I was thinking...essentially a super fine grit, since it's not that bad. I'll stop by Ace on my way home from work tonight to pick up a 220 AO flap disc. Should be able to bang this out tomorrow and will post my results.

 

[revco]

Quick update. I checked two hardware stores for a 220 AO flap disc. No can do in this town. So I found a product from 3M that is basically an industrial strength scotch guard pad attached to a bit that can be inserted into a drill. It's marketed as a paint stripper.

Got out my trusty DeWalt, made up a BKF paste and I'm making some progress. It's scratching the interior a bit and I'm definitely taking off metal, but it's not anything I can't live with. I have a few stubborn spots where the slag clearly fused with the SS and these are going to take more work. But, I think this method will work and will be safe. I've proven to myself, though, that a 100 years of scrubbing with a scotchguard pad and BKF would have never done it.

Now that I see how much work this is taking, had I to do it over again, I probably would have bit the bullet and gotten the rough GatorGrit fiber pads. They seemed too strong for my taste at the store, but now that I know how stubborn this slag is...it probably could use it!

I'll probably pick up some 220 grit AO sandpaper for finishing and then give it another coat of BKF with a scotchguard pad. What a pain in the rear!

Lesson learned: Fill the dang keg with water before you plasma cut. Simple solution to a problem that takes many hours to solve.

 

[Breck09]

Quick update. I checked two hardware stores for a 220 AO flap disc. No can do in this town. So I found a product from 3M that is basically an industrial strength scotch guard pad attached to a bit that can be inserted into a drill. It's marketed as a paint stripper.

Got out my trusty DeWalt, made up a BKF paste and I'm making some progress. It's scratching the interior a bit and I'm definitely taking off metal, but it's not anything I can't live with. I have a few stubborn spots where the slag clearly fused with the SS and these are going to take more work. But, I think this method will work and will be safe. I've proven to myself, though, that a 100 years of scrubbing with a scotchguard pad and BKF would have never done it.

Now that I see how much work this is taking, had I to do it over again, I probably would have bit the bullet and gotten the rough GatorGrit fiber pads. They seemed too strong for my taste at the store, but now that I know how stubborn this slag is...it probably could use it!

I'll probably pick up some 220 grit AO sandpaper for finishing and then give it another coat of BKF with a scotchguard pad. What a pain in the rear!

Lesson learned: Fill the dang keg with water before you plasma cut. Simple solution to a problem that takes many hours to solve.

You have a link to that 3M product you are taking about. Sounds like something I could use. Thanks in advance.

 

[revco]

Breck - you bet. It's a 3M paint & varnish remover. Part number 9413NA, purchased at Ace Hardware in the same section as all the grinder bits, sand paper and such. Not sure if it's at Home Depot or Lowes. They also make one of the same version that is designed to applied to a backing, but I didn't have that, so I went with the pre-made one. Here's a photo:

Just be careful not to drag the metal bits along the stainless. It's probably harmless, but easy to do. I got the hang of it within about 5 minutes. It does give the inside of the keggle a bit of a roughness, but I found that BKF and a scotchguard evens it out a bit. I've had to go through, clean it up, find spots I missed and then hit it again a few times. So far, good results though. Probably about an hour to hour and a half per keg, based on my amount of slag.

Hope that helps!

 

[revco]

Well, that's it...problem solved. That little scotchguard on a drill bit gadget did a good job, in my opinion. Probably spent three hours total, but I was particularly thorough and the second keg took less time once I knew what I was doing. After hitting it with a final coat of BKF and a pad, I don't even feel I need to hit it with sandpaper...the SS is smooth and free of all slag/dross. The inside of the keg is certainly not as pristine as it was new, but it's clean enough to cook in now.

I would say this method really wasn't that bad since I didn't have to progressively get finer with further grinding. It's a bit of elbow grease, but the drill was doing 99% of the work. It was also able to clean up the gas coloring from the welds like nobody's business, so now I have nice, shiny welds.

My little pad is about toast after two kegs...so if you're doing three kegs, you might need two pads. I'd say give it a whirl with one and buy two only if you need it. One pad cost me about $12.

Hope this helps others! Good luck, Breck! (This might even remove any concerns of your steel wool treatment! Here's to hoping!)

 

[Breck09]

Awesome to hear man. Going to go find me one tomorrow and work on my kegs this week while on vacation. Thanks for all the information.

 

[revco]

I found a link for this on Amazon:

http://www.amazon.com/3M-Scotch-Brite-Contour-Surface-9413NA/dp/B00004Z4DH/ref=sr_1_1?ie=UTF8&qid=1351378287&sr=8-1&keywords=9413na

A few bucks cheaper than I found it at the hardware store, in case you have trouble locating it. Worth it if you can wait for it.

 

[dmfa200]

Glad to here that all is well with your new keggles.
There are some on this forum that would tell you that you will ruin your equipment if you cleaned it with anything other than PBW and a feather duster.
Don't believe everything you hear.
If stainless steel wasn't as resilient as it actually is, it wouldn't be one of the most used alloys on the planet.
Use only virgin abrasives on stainless and once used, dedicate them to only stainless and everything will be alright.

 

[DaleP]

This advise is a little late for you, but might help others. If you fill your keg with water before cutting with the plasma, the slag won't stick, no clean-up needed.

 

[skipper1953]

I am having this same problem. I used steel wool though before finding out that I shouldn't. Is there any way to make sure I get it cleaned up so I don't have rust problem?

Try searching on "Passivating stainless steel". Google turns up lots of hits. Some can get pretty technical. I think you will find some useful information. You may learn more than you ever wanted to know about what makes stainless steel stainless and what makes it rust.

I think the oxalic acid in Bar Keeper's Friend acts as a passivating agent. That is why it is so good on stainless.

 

[bdjohns1]

I think the oxalic acid in Bar Keeper's Friend acts as a passivating agent. That is why it is so good on stainless.

Pretty much.

At work, we use high-strength nitric acid to passivate. It gets a decent contact time (circulating if we're passivating pipe welds), rinse thoroughly, then air dry.

 

[fork]

Nitric and citric acid will work for passivation. I think citric is easier to find and safer. Although I haven't really found a cheap source for either. I need like 4 pounds to do the inside of a keg I turned into a fermentor. 5 lbs is 20 dollars on amazon but id rather not pay 20 dollars to passivate one thing then dump it down the drain.

 

[graduate]

A good old fashion stainless steel pot scrubber will work.

 

[bdjohns1]

You could probably use less acid if you only put a gallon of solution in there and moved it around periodically (roll, tip, etc.). Since you're using it to ferment, I assume it can be sealed well.