Why passivation matters

[jcaudill]

This picture pretty much shows it all:


photo by brewerJP

It's really noticeable which pot has been passivated and which has not (can you tell? Hint: nickel comes to the front). I've never seen it with my own eyes before so it definitely was an eye opener when I did. Just thought I'd share this as a punch list item for those that weld on their pots or other stainless equipment before putting it to use. I couldn't even imagine having done so without it.

Just to preempt how I did this: I ran a closed loop. Filled the kettle with cold water and an appropriate amount of Leracid KMS and pumped it through my diaphraghm pump into my CIP lid that has a 360 spray nozzle (the one from McMaster). Let this run for 30-40 minutes then racked the solution over to the next kettle and did the same thing. After each run rinse very well and after all is said and done flush the pump, tubing and fittings with a lot of fresh water.

Hope this is useful to someone!

 

[ThreeDogsNE]

I have similar pots, but just the plain pots, without any nice triclover adornments or other fittings. They look good with a scrub with Barkeeper's Friend. Would this work after welding, for those without all the other nice hardware?

 

[dutchoven]

Bar Keepers Friend should work on your welds ... From what I've heard, repassivation happens pretty quickly after the acid is removed.

 

[jcaudill]

FWIW - The right pot represents a BKF scrubbed pot and the left is the Leracid. I think BKF is better than nothing - but if you look at the master brewer guidelines you need a pretty heavy concentration of acid (they say up to 50%!) and you have to run it for at least 30 minutes. In lieu of nitric acid they said you can use Citric acid which is a lot safer to handle.

I think BKF is probably great as a maintenance passivation but for the initial passivation not the answer.

 

[jcaudill]

Oh and to respond to the remark about fancy fittings: it's not just about the fittings. It's about changing the structure of the stainless to bring the nickel forward and prevent rusting. I'm guessing most pots are not passivated when you get them.

 

[Texan]

Oh and to respond to the remark about fancy fittings: it's not just about the fittings. It's about changing the structure of the stainless to bring the nickel forward and prevent rusting. I'm guessing most pots are not passivated when you get them.

As I understand passivation - It does not bring out or forward nickel to the surface. Stainless has chromium that helps inhibit the rusting. Passivation is the creation of a thin oxidized layer that prevents oxygen from contacting the iron on the surface of the stainless.

Passivation usally involves stainless surface areas being in contact with a % of acid concentration to form the barrier. This barrier can be scratch or worn down where you can repassivate as needed.

With bad welds sometimes you can not get in the micro areas to passivate resulting in rusting/corrosion.

Nickel alloy metals are normally used in applications where chemical reactivity is concerned.

 

[jcaudill]

It actually really depends on the composition of the metal phase of the stainless steel as to what that passive layer is actually compromised of but it's some combination of chromium, nickel and/or molybdenum which are all responsible for the anti-corrosion of the stainless. So it just depends on how you look at it but that layer is based on original composition and nothing just created out of thin air.

It should be noted that the passive layer created by acid is considered to be stronger than the natural passive layer which is why passivation is some form is important for both the equipment and quality of your beer.