brown scratches on stainless

[kondi]

I am using a BIABasket in my 304 SS brewing kettle and I realized that taking the basket in and out makes lot of scratches on the inner surfaces of the kettle. As I read, usually a few small scratches are OK, but I have a mark that is a bit deeper and it has a brownish tint. I am afraid it is rust, could it be? Or what else is it? Can I treat/fix it somehow?

On the attached photo you can see my (sadly) usual, longer vertical scratches, but in the middle, there are three marks that look suspicious. I think it was made by the legs of the basket.

 

[day_trippr]

Not only could it be "rust", it probably is. The scratch breached the chromium oxide layer exposing the amalgam of stainless and steel, and the latter has oxidized.

Looking at all those scratches I would definitely go through a passivation process using a weight-based 4-5% Citric acid solution. That will chew up all the exposed iron. Let it sit filled with the acid solution for 8 hours or so, then do the first rinse with low mineral water if possible (distilled preferred, RO is ok as well). Subsequent rinses can use tap water. Dry thoroughly and let sit, and the chromium with oxidize and hopefully seal up all those scratches...

Cheers!

 

[Gruel]

I don't think these kettles are an 'amalgam of stainless and steel'. Actually, I've never heard of such a thing.

Regardless, passivating after removing the corrosion is a good idea. These spots could be contact corrosion where the basket (also some type of stainless, I assume?) touched the kettle while in a weak acid (aka mash or wort). I would give those spots a good scrubbing with barkeepers friend to completely remove the discoloration before doing the citric acid treatment.

 

[day_trippr]

I'm not a freakin' metallurgist ffs. I should have said "alloy". Either way,
there are iron particles in stainless steel, and if exposed to air, they rust!
Sheesh...

 

[kondi]

Thank you for the answers!

Unfortunately, I can not get barkeepers friend in my country I can get easily TSP, sodium percarbonate (OxiClean), sodium carbonate, sodium bicarbonate, vinegar, "Grainfather High Performance Cleaner", starsan, various acids, bleach.

Regardless, passivating after removing the corrosion is a good idea.

How shall I remove the corrosion? I will passivate after with citric acid.

(also some type of stainless, I assume?)

It is supposed to be - but was ordered from China...

 

[Gruel]

Geez, didn't mean to annoy you, day_trippr (hope that's not too empathic for you...).

Stainless is usually a combination of mostly iron, some nickel and some chromium, plus very little of some other stuff. 304 is 18-20% chromium, 8-12% nickel, almost all the rest is iron. Normal 304 has up to 0.08% carbon, 304L up to 0.03%. (Important for heat sensitization; the less carbon, the less chromium carbide can form). 304/304L is mostly austenitic, with a small percentage of ferrite (depending on the exact percentages of nickel and chromium), which is a good thing, since the ferrite can absorb impurities (sulfur, phosphorus) when you melt and very rapidly cool the steel, for example in laser welding.
Now you know as much as I do about 304.

Barkeepers Friend is oxalic acid plus some other stuff.
I'd stay away from chlorine bleach, and mechanical abrasion with steel wool would be my last choice. Maybe just some non-metallic scouring pads? Or very fine sandpaper?

Ok, I just googled it: citric acid will remove rust. So maybe some scrubbing with citric acid on the rust spots (if that is what they are; worst case it's just some burnt-in sugar, and it will also come off...), and then the passivation. I'd passivate that basket as well.

 

[RPh_Guy]

Can you get citric acid?

This article provides comprehensive and accurate info about passivation:
https://***************.com/wiki/Passivation
There's no need to remove the rust beforehand. No BKF. No abrasive pads. No sandpaper. Using abrasive products just decreases the surface's corrosion resistance and makes it harder to clean.

 

[kondi]

Can you get citric acid?

There's no need to remove the rust beforehand. No BKF. No abrasive pads. No sandpaper. Using abrasive products just decreases the surface's corrosion resistance and makes it harder to clean.

Yes, I can. That is what I will do. Thanks!

I will have my RO system ready in about a week, TDS in my tap water is 200 ppm. At some places, I read I should not rinse the acid, just dispose the solution and let it air dry. What do you think about this? I could either wait for RO or do it now, does time matter? If I do now, I can use tap water, skip rinsing, or buy expensive distilled water, which I would prefer to avoid...

This article provides comprehensive and accurate info about passivation:
https://***************.com/wiki/Passivation

Hmm, I see a familiar photo there

 

[day_trippr]

[...]
Now you know as much as I do about 304.

[...wait for it...]

Ok, I just googled it: citric acid will remove rust. [...]

 

[RPh_Guy]

I will have my RO system ready in about a week, TDS in my tap water is 200 ppm. At some places, I read I should not rinse the acid, just dispose the solution and let it air dry. What do you think about this? I could either wait for RO or do it now, does time matter? If I do now, I can use tap water, skip rinsing, or buy expensive distilled water, which I would prefer to avoid...

It should be rinsed after passivation. Ideally the water should have low chloride.
It's fine to wait if you want. As long as it's not moist the rusting won't get worse.

Hmm, I see a familiar photo there

Yes, thank you. I can add your name to it if you want.

Cheers

 

[moorejl57]

You can also use Star San (phosphoric acid based) at 4X normal strength, but the 4-10% citric acid solution will be less expensive. I use citric to descale my espresso machine and it is much more active when it is hot. So you can fill your brewing system with the solution and heat to mashing temp or so and let sit 20 min minimum.

 

[kondi]

You can also use Star San (phosphoric acid based) at 4X normal strength, but the 4-10% citric acid solution will be less expensive. I use citric to descale my espresso machine and it is much more active when it is hot. So you can fill your brewing system with the solution and heat to mashing temp or so and let sit 20 min minimum.

I will do a hot citric acid bath, for a few hours, rinse with low TDP water and let it air dry.

I know, I asked the question... But based on my further readings, I concluded the star san method is not effective for this. (Anyway, it's more expensive, as you wrote)

Yes, thank you. I can add your name to it if you want.

No need.

 

[jptweb64]

I've used full strength star sans before on scratches. Why full strength? Mainly to keep it in gel form so that it will stay on the vertical surface. Just a small dab on a rubber spatula and smeared over the scratches. It won't drip off. I usually leave it on for several hours and completely rinse off.

 

[RPh_Guy]

You can also use Star San (phosphoric acid based) at 4X normal strength

I've used full strength star sans before on scratches. Why full strength? Mainly to keep it in gel form so that it will stay on the vertical surface. Just a small dab on a rubber spatula and smeared over the scratches. It won't drip off. I usually leave it on for several hours and completely rinse off.

FYI Star San (phosphoric acid) does not passivate, and therefore it is not ideal for rust removal on brewing equipment.

 

[bracconiere]

just curious....i'm not concerned really with a scratch...but it's not going to cause me to get a rust hole is it? i've had my pot for like 18 years, don't want to lose it now, if all i would need to do is dump some citric acid in it once when i'm soaking it for a scrub.....

 

[Bilsch]

just curious....i'm not concerned really with a scratch...but it's not going to cause me to get a rust hole is it? i've had my pot for like 18 years, don't want to lose it now, if all i would need to do is dump some citric acid in it once when i'm soaking it for a scrub.....

Once the rust gets started in a spot, it just keeps going. And yes it can/will go right through. How long that will take is anyone's guess. For how and why to passivate.. best to read RPh_Guy's well written and researched article he posted a link for.

 

[bracconiere]

Once the rust gets started in a spot, it just keeps going. And yes it can/will go right through. How long that will take is anyone's guess. For how and why to passivate.. best to read RPh_Guy's well written and researched article he posted a link for.

guess i know what to do with that half a 5lb bag of citric acid i got left from either making homemade PBW, or dishwasher soap now.....


can i PBW it, AND add the citric while it's doing the PBW soak...i did see it's supposed to be low mineral water.....

 

[Bilsch]

guess i know what to do with that half a 5lb bag of citric acid i got left from either making homemade PBW, or dishwasher soap now.....


can i PBW it, AND add the citric while it's doing the PBW soak...i did see it's supposed to be low mineral water.....

No you don't want to add those two together because one is basic and the other acid. They will essentially cancel each other out.

 

[bracconiere]

for some reason i thought pbw acidic for a second....so it'd be like trying to make refrigerator pickles with baking soda for sodium, and vinegar for tartness......


edit: hmm, i think heard they use sodium acetate for potato chips though.....could be good on a burger!

 

[day_trippr]

The Star San/phosphoric acid passivation myth shall never die - there's clearly no wooden stake big enough or enough silver bullets to put it down.

Anyway...anyone mixing up a kettle's worth of citric acid should gather up any other SS gear that could use some cleaning up and either fit it in the same vessel or recover the mix in another vessel and reheat it for re-use (you can get extra mileage out of it). When I passivized my SS IC that got dinged up a bit while threading gap-forcing SS wire through the loops I used the same solution to clean up my 6x20" SS spider (which looked waay better than brand new afterwards)...

Cheers!

 

[bracconiere]

the only stainless i have is my pot, and my mash paddle.....guess i could toss it in, but the handle won't fit all the way down......(i think my bazooka tube is aluminum....)

 

[day_trippr]

I've never heard of an aluminum bazooka tube - even homemade ones?

Cheers! (That would be bad, mkay? )

 

[bracconiere]

hmm, it doesn't look very stainless like......just assumed...

 

[MikeCo]

My SS Brewtech brew bucket quick start guide recommends Starsan for initial passivation. I used citric acid because it's cheaper, but why do they recommend Starsan if it doesn't work?

 

[Jtvann]

My SS Brewtech brew bucket quick start guide recommends Starsan for initial passivation. I used citric acid because it's cheaper, but why do they recommend Starsan if it doesn't work?

Short answer, because they're wrong.

 

[kondi]

I have got the citric acid and RO filter will arrive tomorrow.
I was thinking, what if my BIABasket is actually not stainless? They claimed its 304, but if not, would not it ruined by the acid bath? Can I check it first on a small spot before? How can I validate it?

 

[moorejl57]

FYI Star San (phosphoric acid) does not passivate, and therefore it is not ideal for rust removal on brewing equipment.

Just read the article on passivation and pickling in the wiki, very informative and helpful. I am kind of stunned on how much misinformation there is out there on Youtube. Thanks for the education!

 

[RPh_Guy]

I have got the citric acid and RO filter will arrive tomorrow.
I was thinking, what if my BIABasket is actually not stainless? They claimed its 304, but if not, would not it ruined by the acid bath? Can I check it first on a small spot before? How can I validate it?

Well, stainless and aluminum look different.
The oxide layer on aluminum is dark/dull:

[...] my mash paddle.....guess i could toss it in, but the handle won't fit all the way down.

That's what I do.

 

[bracconiere]

That's what I do.

i still wish they had a puzzled reaction......i read that with a straight face a couple, times, then started laughing.....

 

[RPh_Guy]

i still wish they had a puzzled reaction......i read that with a straight face a couple, times, then started laughing.....

?? I meant I just passivate the part of my mash paddle that fits in the kettle. I only care about passivating the surfaces that come into contact with wort and beer anyway, so it's perfectly fine.

Cheers

 

[bracconiere]

?? I meant I just passivate the part of my mash paddle that fits in the kettle. I only care about passivating the surfaces that come into contact with wort and beer anyway, so it's perfectly fine.

Cheers

LOL, NVM....