High temperature service performance of sacrificial anodes

[Chadarchie]

I am looking for any information (e.g. life expectancy, measured potentials) about operating sacrificial anodes (galvalum I, galvalum III, Magnesium H-1 Alloy) at elevated temperatures - up to 200C (392F). Any experience/information/references especially with galvalum III over 100C (212F) would be helpful.

 

[unclesyd]

Come back with more details of the enviroment and conditions that you are considering.

Just remember that for an anode to work it has to dissolve form metallic salts that have to go somewhere.

 

[Chadarchie]

We are protecting internally coated tanks which will contain an oilfield produced water phase. Resistivities averaging 100 ohm-cm, but vary from 10 ohm-cm to 500ohm-cm. Do you have any experience at these temperatures?

 

[unclesyd]

I just check this morning and the highest temperature we have used Galvalum III is 65°C.

We did test some higher temperature services using different type anodes. Presently I don't have access to the results information. My recollection is that we experienced some very high anode dissolution rates.

I would check with CPT or Corrpro

http://www.cpt.net

http://www.corrpro.com

 

[Chadarchie]

I've tried Corrpro. They sent me a brochure on Galvalum, which has data up to about 100 C. I know dissolution will be higher, but I'm trying to quantify/approximate how much higher. I know that resistivy goes down with temperature, which may confuse some people into thinking some other mechanisms are involved. Results seem to flatline for performance above that temperature. This makes sense because I've read the corrosion reaction actually decreases slightly above 90 or 100.

Anybody else have any data?

 

[stanweld]

I have had experience using sacrifical Galvalum anodes up to about 325 F in similar applications. One of the principal problems initially encountered was rapid wastage of the anode and subsequent cathodic disbondment of the internal coating and corrosion of the carbon steel base metal. Initial solution involved limiting the surface area of the anode exposed to the environment by encapsulating nearly 90% of the anode surface. Even so, some disbondment of coating immediately adjacent to the anode attachment location occurred. Type 316L stainless steel cladding was eventually selected for equipment exposed to similar environments.

 

[Metalguy]

I've seen a comment somewhere (long ago) that zinc anodes become cathodic to steel above some temp. The temp wasn't all that high--IIRC it was a home hot water heater.