More likely it is Zn either from rust preventative coatings or oils and grease used in assembly. I can't see a mechanism for solective de-alloying of brass in oil.

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I would start with a call to the fluid maker as they will have far more experience with their own product. Then I would place a handful of brass into a heated glass bottle of stirred fluid with samples sent for analysis of the fluid before introducing the zinc and then every few days for a week.

My guess, if it was leaching just zinc the brass would shift to majority copper on the surface and become obviously copper colored.

Note that manufacturers only test for what people are interested in; we've had occasion to have had issues with boron contamination of stainless steel, and no manufacturer tests for it, or is even aware that there is boron in their steel at all.

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Hydraulic oil normally contains 1000+ ppm zinc. You mention fhari, is this an oil or water based lubricant? Brass and zinc plated fittings have been a concern in systems in the past but only if fluid had a high sulfur content.

EdStainless (Materials)4 Oct 20 18:05
More likely it is Zn either from rust preventative coatings or oils and grease used in assembly. I can't see a mechanism for solective de-alloying of brass in oil.

About the rust coating it is a CuAl based system, so no zinc plated items on it for exemple. I will check the possibility of grease or oils, but the sysyem was already flushed and got the good classification of the oil.

3DDave (Aerospace)4 Oct 20 20:42
I would start with a call to the fluid maker as they will have far more experience with their own product. Then I would place a handful of brass into a heated glass bottle of stirred fluid with samples sent for analysis of the fluid before introducing the zinc and then every few days for a week.

My guess, if it was leaching just zinc the brass would shift to majority copper on the surface and become obviously copper colored.

We hope to not open the circuit, but when we have too we are going to check for the connectors if there is any color chance....

TugboatEng (Marine/Ocean)4 Oct 20 23:22
Hydraulic oil normally contains 1000+ ppm zinc. You mention fhari, is this an oil or water based lubricant? Brass and zinc plated fittings have been a concern in systems in the past but only if fluid had a high sulfur content.

More details about the oil: houghto safe 200x oil


Thanks you all!

From the SDS, one compound present is a solvent (oxydiethanol) and the other is an emulsifier (dibutylamine) so it seems a small amount of oil contamination could be easily dispersed into the system if there were contamination.

Um, Houghto-Safe 200 is not even an oil, it's a water-glycol mix more akin to radiator coolants. It may have used up whatever buffer they provide it with as a corrosion inhibitor (if it had any to start with), at which point, yes it will start to pick up zinc from the fittings. As glycol ages, it oxidizes to glycolic acid (just like ethanol oxidizes to acetic acid or vinegar) and becomes even more aggressive. I'd suggest you talk to the vendor who sold you this fluid and ask about corrosion inhibitors. One thing to do with glycol mixtures is to check the pH (should be quite basic, near 8-10 when new from the container) on a regular basis and replace it or replenish the corrosion inhibitor/buffer when it starts dropping below about 8 or so. If you must run a glycol/water mix, you should look into getting all the fittings in stainless steel or similar corrosion resistant materials (e.g. no brass or galvanized steel). It sounds like you don't have any known brass fittings, but do you know if any of the circuit controls (valves, regulators) contain brass? Do you see any increase in iron (indicating corrosion of typical spool valve materials)?

Guess you have already checked that there are no galvanized items in the system.

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