316L corrosion rate as chlorides increase

[jvs3]

I have a brine concentrator and am evaluating an increase in the chloride concentration by a change in operation. Specifically I am trying to quantify what increase in corrosion to expect.

The brine is brackish water with 2200 ppm chlorides at 100 degrees C.

Existing materials include titanium (which I'm not real concerned about), 316l welded with 317l filler, 316l welded with 316l filler and plain 316 welded with 316.

We have experienced SCC of the 316l stainless and pitting attack on the sub 317l filler welds.

I'm interested in the how the general corrosion rate of the different metals increases as I increase the chlorides to around 11,000 ppm. Using that information I'll determine the maximum acceptable chloride level versus corrosion rate and operate there.

Any online references would be preferred but any references at all appreciated.

 

[Metalguy]

Cl attacks 316/317 SS via local corr. (pitting), not by general corr. (wastage), and by SCC. At 100 deg C, it doesn't take much Cl-far lower than what you have. 317 is only slightly better.

 

[jvs3]

I don't have a choice of materials here as the material is existing.

I'm trying to determine material life expectancy given an increase in the chlorides. Everything is a tradeoff...I need to determine how fast my equipment gets eaten up by processing worse brine. The decision to process the higher chlorides brine has already been made but I can determine how much. Make sense?

 

[Metalguy]

I'm not sure you can quantify this issue. If you had pitting before, you can expect more.

Perhaps you can change the operation-it's the stagnant periods where Cl pits the SS. If you can minimize that you'll get less pitting. Crevices are extremely bad too.

 

[mcguire]

Go to the Nidi.com website and look for the work by Alan Haynes or others. There are well-established relationships between the influence of external variables such as pH, chloride concentration and temperature on pitting. You can also determine the influence of material variables.
I put some stuff in an FAQ above, but it needs undating. In general, the influence of chloride level and temperature are exponential, so look out. You will not find adequate information on materials anywhere. The state of knowledge on pitting is really pretty poor and there is a lot of B.S. in print.