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Rust prevention on Stainless Steel Misting Nozzles and Refurbishment after clogging

July 1, 2011

I have questions on 2 related topics -

1. I am using 303 Stainless Steel misting nozzles in a water based application. I am using these nozzles to avoid rust, which can cause clogging of the nozzle. What I find is that I am still getting rust problems. The manufacturer says it is caused by specks of carbon steel tooling that end up on the part and that an extra passivation treatment is required to completely avoid rust. However, the nozzles are fairly expensive already and I am not purchasing them in large enough quantities to justify the additional expense. Are there any small scale "do-it-yourself" treatments that can be performed to prevent this type of rusting problem?

2. Another common clogging problem with nozzles is residue from solids found in the water after it evaporates. The passage ways in the nozzles are very small - on the order of 0.1 mm. I have found that bathing the nozzles in a diluted mixture of muriatic acid for a short period of time (less than 3 minutes) typically clears up the clog. However, I see posting all over the Internet not to use hydrochloric acid on stainless steel. What are the negative ramifications of using muriatic acid on my parts? There is some discoloration and dulling of the stainless steel surface, but cosmetic appearance is not a problem for me. Are there any longer term problems I need to be aware of? Has the integrity of the surface been compromised, such that rust may occur after the treatment? How long will it take for the parts to rejuvenate its chromium-oxide passivation layer? Are there any other treatments you might be able to suggest for unclogging the nozzles?

Pete Sites
System Designer - Jacksonville, Florida, USA

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These nozzles can be passivated in bulk, so the process should be inexpensive.

Muriatic acid will attack and eventually destroy stainless steel, and in the meantime will promote rusting. Try using dilute (15-20%) phosphoric acid instead.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
First of two simultaneous responses -- July 1, 2011

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Second of two simultaneous responses -- July 4, 2011

I used to work in a very different line of business where we had to try and keep one product iron contaminant free during a mixing and bottle filling operation otherwise it would degrade.
To do this we made sure all the mixing equipment and filling lines were manufactured from 316 stainless and regularly re-passivated the filling lines.
We did this by passing nitric acid solutions through the mixers and filling lines. The time varied depending on the strength of the acid.
Typically the lines were left overnight with 8-10% nitric acid. The lines were then flushed with deionised water.

Ciaron Murphy
Aerospace - South Wales, UK

First, I would buy a second set. When you have a problem, replace that one or all of them. Take the used set and soak it in a 40% solution of nitric acid for 30 to 60 min at room temp.. This can be used several times before neutralization and disposal.

James Watts
- Navarre, Florida
July 5, 2011

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You can both passivate and remove the hard water deposits safely and easily using a citric acid based solution. Let us know if we can help.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

July 6, 2011

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August 25, 2011

We have found that using a mix of vegetable soap, sodium carbonate / washing soda [affil links], sodium metasilicate [affil links], and nitric acid works extremely well as a hard water (calcium and magnesium cleaner) water softener and rust protection (sodium metasilicate [affil links]).
Flush the entire system with this mix (with water)
Use a venturi to draw the product into the system and through the nozzles.
Your whole system will be cleaned and well maintained. We do this for Dupray steam machines, pressure washer [affil links], etc.

Darren Olson
- Toronto Canada