Whats the matte finish inside a keg?

[ParanoidAndroid]

I started on a keggle and got the top off. I noticed the inside has a matte finish that can scratch fairly easily. When its scratched, the finish wears off and the steel becomes shiny as stainless should.

1. Does anyone know what the finish is?
2. Is it harmful if it comes off while cleaning?
3. Does it ruin the inside of the keg if its scratched?

You can see it coming off inside the center circle.

 

[HDIr0n]

I believe it is just passivated stainless, basically it is a protective layer of oxidation. It will not harm anything, and it will be fine if it is scratched. Try not to scrub or scratch it with anything ferrous which can cause rusting.

 

[day_trippr]

I'd be a bit more leery. I have a crap ton of passivated stainless steel in my home, and none of it is "easily scratched" or has a "matte" appearance...

Cheers!

 

[ClaudiusB]

I'd be a bit more leery. I have a crap ton of passivated stainless steel in my home, and none of it is "easily scratched" or has a "matte" appearance...

Cheers!

Same here, all very shiny.
What about calcium oxalate deposits, also known as beerstone.

Cheers,
ClaudiusB

 

[ParanoidAndroid]

Hmm, weird.

It covers the whole inside of the keg too. Its not just where the old bud light was for a couple of years. If that was the case then the matte area would only cover 1/4 of the keg.

I might try and boil some water in there in the next couple of days to see if it does anything to it.

 

[wickman6]

Some hot water, pbw or oxyclean and a scotch brite sponge will rid the keg of that matte finish I'm thinking. My oldest corny kegs are nice and shiny on the inside and that's how they got that way.

My newest kegs also have a matte finish on the inside. I think its simply unpolished stainless. I've never had problems with it. Stainless is only really shiny if It's been polished or had some other abrasive treatment, in my experience.

 

[Homercidal]

All of my kegs look like that. It's just the surface of the SS. I wouldn't say it's *easily* scratched, unless you mean can I scratch it with light pressure from something like a screwdriver. Maybe not with my fingernail...

 

[WalterAtMarchPump]

It can also depend on what kind of passivation was done to it. Some process use a caustic soda as the first step to degrease and clean the part...then they get rinsed with water and put into a nitric acid bath, rinsed again and back to the caustic and then final rinse....most of the parts we send out for passivation turn out like this...
We also do some really basic passivation on some of our custom one-off pumps in-house and we use a citric acid bath...it gives stainless that type of finish and it will turn shiny if scratched like yours. (but the stainless we start with is not shiny or smooth to begin with. Machined surfaces will stay nice and shiny though)

And like it was mentioned above....passivation is just an oxidation layer....it can be scratched through...the whole point to it is to have the acid eat off any stray iron particles (that's what can cause stainless to start rusting)

 

[SpentGrains]

My newest kegs also have a matte finish on the inside. I think its simply unpolished stainless. I've never had problems with it. Stainless is only really shiny if It's been polished or had some other abrasive treatment, in my experience.

Right, most likely just unfinished stainless, kind of like aluminum foil has one "shiny" side and one matte side.

If you want to reassure yourself put a flame to the top you cut off- if it peels or burns off it is a coating, if it discolors or does nothing it's just stainless.

 

[ParanoidAndroid]

Maybe I shouldnt have said easily...but the scratch is from me cleaning it with a big keg brush. The end of the brush scrapped the inside of the keg. I cleaned it with the Free Version of OxiClean

 

[HDIr0n]

Bottom line, you are fine even of you have some scratches on it. Just don't go crazy with scrubbing it, or going at it with anything ferrous and rusty.