Chlorides corrosion in acetic acid solutions 3

[kbarratt]

We have linked 316L failures to stress corrosion cracking but we only appear to have low chloride levels.

What levels of chlorides could be expected to cause corrosion in 316L stainless steel containing 30% acetic acid solutions at around 40 degrees centigrade?

Could the Palintest for chlorides be failing to pick up the chlorides for any reason?

Thanks in advance for any advice anybody can offer.

 

[mcguire]

kbarratt
There is literature that calls stress corrosion cracking chloride cracking. This is a disservice that has arisen from different commercial and academic factions pushing their own theories and solutions to SCC. If the environment causes pitting then it is capable of causing SCC if stress is sufficient and the correct temperature exists. You have the acidty and temperature to get pitting with very small amounts of chloride in 316, say 1000ppm, so having SCC is not a surprise.
There are a number of controllable material variables within 316 which can mitigate this problem, but I think you have the correct problem identified.

 

[hacksaw]

SCC can occur at remarkably low chloride levels i.e. considerably less than 10 ppm in acidic environments.

where is the material being attacked and under what stress levels?

 

[mcguire]

I agree with hacksaw. If you wait long enough, lower levels of chloride than I cited could be sufficient for cracking.

 

[kbarratt]

Thankyou both for your responses - the levels we are detecting are around 20 ppm at most. Thanks for the confirmation that this is sufficient to cause the problem.

 

[Metalguy]

Kbarratt,

Is your SCC transgranular? If Cl is the cause you should find it via SEM/EDAX in the cracking.