Does Nitric Acid Expire? (Shelf Life)

B

barkranch

I am trying to determine if passivation chemicals expire. We were recently dinged in an audit because our procedure states to verify the shelf life has not expired for passivation solutions. I have performed extensive research trying to determine if nitric acid expires. One of the chemical companies we have purchased nitric acid from in the past provided us with a certificate of analysis which states the shelf life is 18 months. We have sense changed suppliers and our current supplier of nitric acid states there is not an expiration date. I realize that shelf life and expiration dates are two different things. Shelf life is for unopened product, expiration dates begin once the product is opened. Do other companies document their expiration dates for passivation solutions?

Any help is greatly appreciated!
:bonk:
 

Miner

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Re: Does Nitric Acid Expire?

I cannot answer your specific question pertaining to Nitric acid, but can comment on the expiration date. Many suppliers will add an arbitrary expiration date to their products simply to limit potential liability exposure and/or potential requests to return the product. This is done even when the product would theoretically last forever.

Having said that Nitric acid will have some shelf life. Light and temperature will cause nitric acid to decompose into Nitrogen oxide, water and oxygen resulting in a yellow coloration.
 

Mikishots

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I am trying to determine if passivation chemicals expire. We were recently dinged in an audit because our procedure states to verify the shelf life has not expired for passivation solutions. I have performed extensive research trying to determine if nitric acid expires. One of the chemical companies we have purchased nitric acid from in the past provided us with a certificate of analysis which states the shelf life is 18 months. We have sense changed suppliers and our current supplier of nitric acid states there is not an expiration date. I realize that shelf life and expiration dates are two different things. Shelf life is for unopened product, expiration dates begin once the product is opened. Do other companies document their expiration dates for passivation solutions?

I'm not in agreement with your definitions. Shelf life refers to quality, the latter to safety. A product that has passed its shelf life might still be safe, but quality is no longer guaranteed.

We also passivate steels in my workplace, but we go through a fair amount of solution; if you are in a position to be worrying about dates, you're carrying too much product.

There are many types of nitric acid; some change with exposure to air, some with temperature, etc. I titrate mine with a base solution to determine if it's within my required parameters - I couldn't care less about a date because that doesn't take into account ANYTHING other than time.

Your issue with the auditor came up because you said you were doing something that you weren't. My suggestion is to remove it from the procedure unless you are mandated to have it there (by regulation or law, for example).
 
B

barkranch

Thank you Mikishots. I totally agree with your comments. You're right, we were not doing what we said we were going to do. We are updating our spec. accordingly, but at the same time I would like to respond to our auditor and say that we have investigated the issue. I'm trying to determine if checking expiration dates are required by law. Since I have no idea how to titrate the solution, I would much rather have the manufacturer give me an idea of how long their product lasts. I have called two nitric acid manufacturers and one said the shelf life is 18 months, the other told me the product does not expire. Nothing lasts forever, so I'm scratching my head on this one.
 

Mikishots

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Thank you Mikishots. I totally agree with your comments. You're right, we were not doing what we said we were going to do. We are updating our spec. accordingly, but at the same time I would like to respond to our auditor and say that we have investigated the issue. I'm trying to determine if checking expiration dates are required by law. Since I have no idea how to titrate the solution, I would much rather have the manufacturer give me an idea of how long their product lasts. I have called two nitric acid manufacturers and one said the shelf life is 18 months, the other told me the product does not expire. Nothing lasts forever, so I'm scratching my head on this one.

Yes, but 18 months in what conditions? In my own experience, nitric acid won't be drifting out of spec for passivation use. We're using 42? B? at 200g/L. Time isn’t really a factor. Now, if I was doing analytical chemistry and I needed total control over the acid, I’d always titrate first.

I have never seen a legal requirement for checking expiration dates for nitric acid (used in a passivation process). It would be a complete shock to me if there was one.
 
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Mikishots

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Thank you Mikishots. We use 42 degree as well.

Yep, seems to be a good standard. On a side note, you can gauge effectiveness of the solution (including the other constituents like sodium dichromate) by the results of copper sulfate tests. If iron is not being effectively removed, it'll show up in about five minutes of applying the copper sulfate.
 
B

barkranch

Yes, we have tested parts using the copper sulfate test. Thanks!:agree1:
 

Mikishots

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Nitric acid is extremely caustic. Wouldn't it be tragic its shelf life is longer than its container.

If the packaging is from the manufacturer the acid is stored properly, it can be kept for a long time. Smaller quantities are typically shipped in brown glass bottles, while industrial amounts are kept in stainless steel kegs or barrels. It's always a bit of an event to watch the guys dump and replenish the deox and passivation tanks. Grab a sandwich and watch them through the glass for a bit of lunchtime entertainment!

Nitric acid is a weird beast, and even needs to be stored separately from other acids - it's an incredibly powerful oxidizer and reacts with just about everything. Kinda like that one kid we all knew in grade school.

EDIT: I suppose it would be worthwhile to talk about shelf life a bit more - it really is dependent on the concentration of the acid in question, and the temperature it's stored at. The stuff we're talking about in this thread is 42 Baume, or 67% Nitric Acid (the balance being distilled water). If we really wanted to slow decomposition (the yellowish tint cause by the formation of nitrogen dioxide), we'd keep it refrigerated. Warm it up and it'll decompose faster. 42 Baume will boil at 121 Celsius, causing rapid decomposition.
 
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