Chloride level in carbon steel pipes 1

[pulkas]

Hello,

I'm working on a waste minimization project and I have a problem. We want to reuse wastewater in a cooling system. This cooling system is made of carbon steel and partly SS304. The chloride concentration is now at a maximum of 210 mg/l. Due to the reuse of water the chloride level will rise. My question is: what is an exceptable concentration of chloride for carbon steel pipes. (latest design: chloride conc. 350-500 mg/l, exceptable??)

I hope anyone can give me an indication.

Tymon

 

[mcguire]

Carbon steel does not form a passive film to protect it from corrosion. Therefore, the action of the chloride ion, which destabilizes passive films in stainless, is not very important to carbon steel. The rate of attack of carbon steel in both fresh water and tropical sea water is between 5 and 10 mils/year ( 2 and 4 mm/year).
The stainless will be ok at this level of salinity ( if at room temperature and neutral pH), but be cognizant of the risks to the carbon steel of galvanic corrosion and the build-up of Fe concentrations, which are deleterious to stainless.

 

[pulkas]

Thank you mcguire,

now the chloride level isn't a concern I can go on with the project.

Beside chloride the used waste stream contains a lot of other contaminants, but not in large quantities. It comes from a biological watertreatment facility, any possible problems known with that kind of water? I'm thinking of disolved oxygen, nitrogen containing compounds or microorganismes? Any tips or warnings?

regards

Tymon Vermeulen

 

[mcguire]

Let's focus on the more vulnerable carbon steel. It benefits from lower oxygen contents. Microorganisms which are sulfur producing are bad. Copper ions are bad.
Is the system closed enough to use corrosion inhibitors?
If not, any nitrates will inhibit corrosion.