Cathodic protection for 316ss in ~3% wt sodium chloride? 1

[kcramp]

Hello!

I have been lurking for quite some time and wanted to talk about some pitting attack that I am seeing inside 316ss vessels...

Operating conditions are solutions containing a plethora of chemicals, but with ~3% sodium chloride at temperatures of 40-85C, agitated (albeit slowly), atmospheric, pH of 5-7, and is a batch process with rinses/cleaning in between. The entire floor of the vessel (and some of the walls) are seeing significant pitting.

Passivation is completed on an annual basis, which I may seek to increase to 6 months based on the severity of pitting I am seeing. Additionally, our passivation process utilizes a citric acid solution followed by a rinse. To promote passive layer formation, I was going to implement a wash of 500ppm paracetic acid as an oxidizer following the citric wash/rinse.

Coating is not an option, and I believe that duplex 2205 would be a good application for this process -- however that is still a ways away on the timeline for funding.

Admittedly I have not done as much research as I should on cathodic protection, but does this seem like a feasible option for these process conditions? Anyone have any thoughts?

Thanks!

 

[EdStainless]

Passivation will not help unless you are getting a significant amount of iron on the surface.
Keeping the surface clean will help. Any fouling or deposits must be removed as soon as possible.
The bottom line is that you have the wrong alloy.
An impressed current cathodic protection system might help, but if you get any fouling it will still pit underneath.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube