[mdkbrew]

Hi All,

I recently noticed that I have a moderately deep scratch about a half inch long in the interior of my stainless steel fermenter.  I'm concerned about the potential for bacteria/dirt/etc. to camp out in there and would like to find a way to grind it away or something similiar.  Has anyone attempted to fix a similar problem?  If so, what tools did you use?  How did you best smooth the surface so as not to make the problem worse with additional scratches in the metal?

Thanks in advance for your help and ideas.

Matt

[Thirsty_Monk]

You need to use NON metallic abrasive.
Something like appropriate grid sandpaper or emery cloth.

[capozzoli]

If the scratch is really deep and you have a grinder you may use a flap disc with a 80-100 grit. Just hit it lightly each pass one direction then turn the grinder 90 degrees and hit it again in order to "cross hatch" the scratch pattern. repeat this till you have taken out the scratch.  

Then take a scotch- brite pad to it to blend it in.

If the scratch isnt that deep you can get away with using only scotch brite or a combination of Emery cloth and scotch brite.

Home Depot usually carries a few different grits of scotch brite. Try starting with one that is more aggressive.  

[euge]

After all this does it need to be passivated again?

[denny]

After all this does it need to be passivated again?

Seems like that would be the safe thing to do.

[capozzoli]

Personally I dont think it needs to be passivated. Passivization is done  mainly to remove any iron deposits that machining or working  may have left behind. If this iron is on the surface it is not a problem and will wash away using water. However if they are driven into the crystalline structure of the surface, or included in a weld or something you can get rust in that spot. For that reason the passivization step becomes very important as a pre-welding preparation wherever "sanitary" welding is required. It will remove any iron particulate that may be present, otherwise it could become an 'inclusion' and make that weld rust.

This is unlikely if you have used flap discs or finishing materials that are not made of iron.

The other reason is to accelerate the formation of the thin invisible oxide layer "passive film" that forms on the surface of the SS spontaneously. You can do that with plain water. Or better yet salt water. Even if you leave it alone for a few days the oxide will form.

But, it for sure wont hurt. Oxalic acid works great for this. That is what Barkeepers Friend is made of and it will both help in removing any residual iron deposits as well as speed along the formation of the passive surface.  

[FlynDutchman]

If the scratch is really deep and you have a grinder you may use a flap disc with a 80-100 grit. Just hit it lightly each pass one direction then turn the grinder 90 degrees and hit it again in order to "cross hatch" the scratch pattern. repeat this till you have taken out the scratch.  

Then take a scotch- brite pad to it to blend it in.

If the scratch isnt that deep you can get away with using only scotch brite or a combination of Emery cloth and scotch brite.

Home Depot usually carries a few different grits of scotch brite. Try starting with one that is more aggressive.  

I would use something more like a 220 or 320 grit flapper wheel. I was a SS Fabricator and used to buff SS for Food and milk lines. Milk lines are realy easy to get contamination so had to have a good finish and was inspected by FDA. After the flapper wheel use Scotch brite pad to polish. Hpoe this helps.

[capozzoli]

Oh yeah, I have heard that the milk stuff is extra strict. Did you ever use one of those blending discs that looks like a big round rubber sex toy?

Defiantly use a finer grit if you can get a hold of them cheap enough.

Welcome to the forum there, FlynDutchman.

[FlynDutchman]

Oh yeah, I have heard that the milk stuff is extra strict. Did you ever use one of those blending discs that looks like a big round rubber sex toy?

Defiantly use a finer grit if you can get a hold of them cheap enough.

Welcome to the forum there, FlynDutchman.

I have used them but not on the milk lines we didn't have to go that fine. I finished up with the scotch brite. They make a pad to go on a angle grinder also. I know when i do my lines they  will all be purged "for those who dont know that is when you weld the inside from the outside".

[capozzoli]

Yeah,Im gonna post some pics of kettles and fermenters im welding up that are back purged.

So, you must have quite a set up,no?

No electropolishing on that milk stuff huh? When ever I sis it it all looks supper polished.

[hopfenundmalz]

Oh yeah, I have heard that the milk stuff is extra strict.

I don't know much about the quality standards for the welds, but this came to mind.  When touring Bell's Comstock production facility, they pointed out that most breweries have dairy quality welds in the piping. Since Kalamazoo was a pharmaceutical center, and there are welding companies that dealt with firms like Upjohn, Bell's has pharmaceutical grade welds throughout the breweries piping.  Impressed me for some reason.

[capozzoli]

No milk welds on what I did today. Oh god Ill tell ya,I assed this guys kettle up today. I dont think it is salvageable. It was my fault. I didnt have anything to do a test weld so I went right into it. I made a couple of mistakes but the real reason I think is that the kettle is so thin. It is one of those really cheap ones I think.

Its melting away before I have even made a mark on the fitting. Im using a gas lens, and I am getting the tungsten tip right in there close trying to keep all of the heat on the fitting. But it is tough.

Finally had to move up from thin filler rod to 3/32 just to get some metal in there before the kettle wall fell away. I dont know, maybe I am doing something wrong.

I hate to pass the buck but I think the kettle needs to be thicker.

What I did wrong though was fill the entire kettle with back purge gas instead of a direct back flow on the weld.

With the wall getting so hot and the fitting drinking up all the heat there is not enough shielding the back is crystallized in at least two spots.

I never have any trouble with keggles but those cheap pots are a b****, unless there is a trick.

Now I am putting off calling the guy to tell him.  Thankfully it is a cheapo.