Sodium Nitrate 304 Chlorides - Problems with SCC?

There is always a potential for chloride induced SCC with the Chlorides present. Your temperatures are ideal for SCC.
At times we had very high levels of the nitrate ion present due to process leaks into the CTW system. We never recognized any correlation between the nitrates and chlorides as measured by SCC.
We tried to maintain low levels of the nitrates due to extensive MIC corrasion problems. We deemed nitrates not very desirable from that point of view.

Uncledsyd,

Thanks for your reply.

Did the system you dealt with have 304 SS and operate under similar temperatures?

Is Nitrate possibly an inhibitor to chloride SCC by preventing chloride enetering ceivices sites of 304? I think I remeber seeing some paper that there are critical ratios which may possibly prevent chloride SCC with Nitrates.

If this is the case, could the nitrate at higher temperatures be a component which could result in SCC resulting to changes in protective oxide breakdown/pitting potentials?

Target nitrate levels for system are 1000 ppm and it ph is kept to 10.

As I stated we have never seen any correlation between the nitrates and chlorides at any temperature or nitrate concentration.
I have never seen an effective chemical inhibitor against chloride induced SCC. We had 5 cooling towers with a total of 21 cells with one tower we could isolate the tower and segments of process for testing with the system as a whole or one of several test installed test loops. I don’t have the data available but I’m sure nitrate levels were tested as far back as the mid 60's with chromates and later without chromates. As stated nitrates where almost an inherent part of the CTW system from leaks caused by SCC. Our worst offender, process wise which operated at 120°C-140°C.

I may get called on this one, but I never seen any practical solution at plant scale for the SCC problem other than keep as low as possible level of chlorides and if you have vertical HE keep the vents open. Other solutions are materials which is not always feasible.