Corrosion in Galvanized Piping with glycol

[cmn8226]

Hello All,

One of our compressors that is going offshore has galvanized piping for the coolant lines(compressor manufacturers called it "hoses are carbon steel which are zinc plated with a clear passivate.")

They have stated that they have used monopropylene glycol and Ethylene glycol (ethanediol) without any problems.

Our operational temperatures is hot and humid (generally 40C at 90-100% humidity)

My question is, is it safe to use this type of glycol-water mix (generally thinking 50-50)? I have heard and read that the glycol reacts with the Zinc in the threads and pipe and cause corrosion.

If not, maybe water with corrosion inhibitor would be safe? (since the lowest temps we might see is 16C)

Thanks for the space!

 

[Metalguy]

Why not consider TSP to raise the pH, sodium sulfite to scavenge oxygen, and a biocide to kill any SRBs? Boilers kill bacteria with high temp, something you don't have.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[unclesyd]

I don't know how much information you can glean from the Evans Cooling. These materials do what they are supposed to do.

http://www.evanscooling.com/maintenance/

 

[btrueblood]

Any standard automotive-grade glycol (aka antifreeze) (ethylene or propylene) should be fine, having much the same inhibitors as metalguy suggests. Then again, this is a closed-loop cooling circuit, correct? Then, provided no path for air to contact the fluid, any corrosion will progress only until the dissolved oxygen in the fluid is consumed. But, yeah, I'd throw some chemicals in there to be safe, and the same ones as metalguy suggests would work with plain water as well.

 

[cmn8226]

Hey guys, thanks for the response.

It is a closed loop system, and as metalguy suggested to use the following:

1. TSP - raises the PH level
2. Sodium sulfite to scavenge oxygen
3. biocide to kill any SRBs

Question is I am not familiar with TSP (Trisodium Phosphate?) - unfortunately my area is mostly mechanical. What would raising the PH do in terms of corrosion?

I found information on the other 2. Is there a on-the-shelf chemical that I can purchase and supply and add to water that contains these?

If I am not concerned with biocide, would be great to get the sulfite/TSP in one additive.

Thanks again!

 

[unclesyd]

I strongly recommend that you purchase a specific product for your system or an inhibitor package for your system. I don't think this is a place for mixing your own as there are too many ramifications involved.

 

[Metalguy]

Raising the pH does little for carbon steel until you get up to ~10.5. At that point the corrosion rate drops dramatically. The downside is that unless you use soft water (very low in calcium), you may precipitate hard calcium carbonate scale if oxygen is present.

If your system doesn't require a lot of coolant, consider using demin. water. You'd then need very little TSP to raise the pH.

Using treated water instead of a glycol mix allows better heat transfer, if that's a concern.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[strider6]

Here are some data on corrosion of galvanized steel in contact with chemicals:

http://www.galvanizeit.org/images/uploads/pdfs/corrosion_organic.pdf

You can also contact the Galvanizeit.org and ask for more data:

"If you would like assistance in determining the reactivity of zinc when exposed to a particular chemical, or if you are interested in a chemical that is not listed in these charts, please contact us online, or call our toll-free technical support at 1.800.468.7732."

http://www.galvanizeit.org/aga/abou.../how-long-does-hdg-last/in-chemical-solutions

hope this help

S.

Corrosion Control

 

[cmn8226]

Thanks for the heads up and the references.

I am going to spec out a pre-mixed additive and just add it to water. I am not sure what kind of water they have available on the off shore rig, but I am positive they have potable water.

I was reading on some good closed loop corrosion inhibitors and came across this:

http://www.amsolv.com/coo-clos.htm

Was looking at this and see some additives I MIGHT be able to use. I'm waiting for the compressor manufacturer to get some input on this. If you guys have any thoughts that would be great.