Black marks on stainless

[Red Raven Brewery]

Hi all.

Last night I got my gear ready to brew this morning and as far as I could see everything was fine and clean etc.

I prepped my water and additions (phosphoric, calcium carbonate and sodium metabisulphate) and left it all ready for this morning.

When I've started to mash in I noticed a strange blackish blotch on top of the malt pipe (see picture). Then I noticed a few specks of the same on the inside of the malt pipe.

Any thoughts? I've carried on with the brew since I had already mashed in half my ingredients so figured what the hell

Any thoughts on this one will be greatly appreciated. And it should go without saying on the future I'll be doing a double and triple check before starting

Cheers all.

 

[crowcrow]

If is doesn't easily rub off I'd assume it is salt pitting in the steal - nothing to worry about - will clean off with vinegar or Barkeepers Friend.

If it rubs off it could be mildew, but guessing it isn't.

 

[Red Raven Brewery]

If is doesn't easily rub off I'd assume it is salt pitting in the steal - nothing to worry about - will clean off with vinegar are Barkeepers Friend.

If it rubs off it could be mildew, but guessing it isn't.

That's what it looked like after I rubbed it off.

I hope it's not pitting. Only got the kit a few months ago

 

[gyurmaember]

Did you use bleach on it?

 

[Red Raven Brewery]

Did you use bleach on it?

No. I use the un-scented stain remover sometimes. Could that have done it?

 

[Brewelder]

That's what it looked like after I rubbed it off.

I hope it's not pitting. Only got the kit a few months ago

If it’s fairly new then it isn’t pitting, stainless doesn’t pit easily anyway.

A damp cloth dipped in some table salt then rubbed on the offending marks should remove them.

 

[Red Raven Brewery]

Here are some more images. With light directly on the spots they look more whitish. Only on the inside and higher up.

 

[Red Raven Brewery]

If it’s fairly new then it isn’t pitting, stainless doesn’t pit easily anyway.

A damp cloth dipped in some table salt then rubbed on the offending marks should remove them.

Sadly the damp cloth and salt didn't work!

 

[Jim Brewster]

Looks to be mostly around where the weld is?

 

[Red Raven Brewery]

Looks to be mostly around where the weld is?

The mark on the top of the malt pipe is over the weld line but the rest isn't on the weld and some of it isn't all that close really.

 

[crowcrow]

Sadly the damp cloth and salt didn't work!

Make sure you wipe the salt off fully or you may get more pitting.

 

[crowcrow]

When I had similar on my ooni pizza oven, Barkeepers Friend got a lot off, but in the end I gave up. I'll have a look at my Klarstein tomorrow, but I've never noticed any like that, but I can believe it looks similar. I try not to add my water additives until brew day (other than a campden tablet)

 

[Red Raven Brewery]

When I had similar on my ooni pizza oven, Barkeepers Friend got a lot off, but in the end I gave up. I'll have a look at my Klarstein tomorrow, but I've never noticed any like that, but I can believe it looks similar. I try not to add my water additives until brew day (other than a campden tablet)

I'm starting to think that was my error. I think I saw something about calcium carbonate being quite bad for it all so perhaps leaving that overnight hasn't done my gear any favours
I'm thinking I need to get bar keepers friend tomorrow and see where that gets me.

I'll be gutted if it's knackered.

 

[Jim Brewster]

If all else fails, wet sanding with a fine grit paper will probably get it off unless the pitting is very deep. Scrub in the direction of the brushed finish and it shouldn't look too bad.

 

[The Baron]

Deffo looks like a chemical reaction, do a search to see what reacts with SS and see if any of it looks similar

 

[crowcrow]

Deffo looks like a chemical reaction, do a search to see what reacts with SS and see if any of it looks similar

As my first post - the chemicals he mentioned are all salts (assuming he meant phosphate, but phosphoric acid will also form a salt) , and salts of all kinds can cause pitting in stainless steel. Even table salt.



Best bet it to polish it out with something like Barkeepers Friend, but ultimately it won't ruin anything or cause issues, it just doesn't look nice.

 

[peebee]

Hmm ... a story?

The lid of my stainless-steel fermenter developed stains and black spots. I cleaned them off easily with Barkeepers Freind (it contains Oxalic Acid BTW). I was careful not to use anything like wire-wool or it may make the problem worse. Used the fermenter and removing the lid showed the marks were back! I tackled the marks a little more severely ... with 81% Phosphoric Acid ("pH Down")! That got rid of them, but the spots merged and took on a dull gray appearance. A few days later the whole area turned black! This was 10mm thick stainless-steel plate (it's a big fermenter!), so I attacked it even more severely with the acid.

Acid won't damage stainless-steel (alkaline will), but it will attack iron. And that is what the acid is attacking, the same way as so-called "Passivation". Passivation occurs spontaneously by oxidising after the rubbish (like iron) has been purged by acid or the like. Stainless-steel contains Chromium which is not worried by the acid, and it is left behind to oxidise and form a protective barrier making the rest of the iron in the steel resilient to corrosion; hence "stainless-steel" (Passivation (chemistry) - Wikipedia ). End of metallurgy lesson (I wish someone would give me one!).

Want to see some "pitting"?

Don't try this on thin sheet stainless-steel! It is only illustrative. The gray pits are where the acid has etched unprotected iron.

Lots of things can damage stainless-steel (destroy the protective chromium content); Alkali, as has been mentioned, for one, bad welding (it's what the likes of "TIG welding" should avoid). Electricity! As I've found: The pitting in that picture is the result of a badly placed "return" electrode clamp following a recent welded upgrade (those marks parallel to the weld lines in the OP look suspicious). But also, not having the chromium in place in the first instance; i.e. badly made stainless-steel.

I'd think those marks in the OP were already there waiting to make an appearance much later? I'd be moaning like mad at whoever sold it me.

Oh aye ... the "black marks"? ... Rust!



[Edit: Minor omissions ... like the strength of acid used.]

 

[Red Raven Brewery]

@peebee that's a great response. Thank you. I did email the supplier and they suggested, like most others, trying bar keepers friend.
I have a feeling regardless of how much I moan the blame will fall on me as I have no real way of arguing about Sus welds etc.

I did however get some bar keepers friend and have used that and the marks now just look like permanent water marks, so that's something.
I'll also be looking at passivating the stainless when I get a chance.

 

[Goldthirst]

Citric acid is good for stainless steel passivation. It works well for removing rust on tools too. I forgot the mix ratio to water but you can find it on Google.