Stress corrosion in absence of oxygen? 3

[btrueblood]

I'm trying to find information regarding SCC in stainless steels; most of the data I find relates to salt-spray and similar atmospheric testing. I have an application where my part will be fully submerged in mostly de-oxygenated water, but possibly with Cl ions roaming around. Is this still a possible SCC environment, or do you need the combined air/salt environment?

Thanks,

Ben T.

 

[mcguire]

One researcher has a chart published in "Corrosion of Stainless Steel" which shows a "safe" area when O is less than 0.1ppm and chloride is less than 10ppm for grade 304.
Another cites failure in boiling MgCl2 is accelerated by oxygen, but still occurring when oxygen is removed.

 

[metengr]

Stress Corrosion Cracking (SCC) in austenitic stainless steels requires three conditions acting synergistically; susceptible material, an applied tensile stress and environment. Since you want to focus on the environment, the main environmental variables that affect susceptibility of austenitic stainless steels to SCC are temperature, dissolved oxygen and chloride content.

The attached technical paper may be of interest to you regarding SCC susceptibility of a molybdenum-bearing stainless steel for use in desalination plant equipment.

http://www.desline.com/articoli/4041.pdf

Although the authors did not specifically look at dissolved oxygen as one of the parameters directly affecting SCC, they do mention specifically in their paper that reduced oxygen content will reduce susceptibility to SCC. I would presume this same situation would apply for your specific application. However, you don't mention material or water temperature.


So, to answer your question in a round about way, austenitic stainless steels immersed in a de-oxygenated aqueous solution should have increased resistance to SCC.

 

[btrueblood]

metengr, mcguire,

Thanks, and a star to each of you. Your answers pretty much sum up my research.

 

[EdStainless]

bt, Just remember the relitive effect of each factor.
Stress, In any assembly that sees temperature cycling or mechanical loading some locations will be at over 75% YS. There is almost always 'enough' stress.
Cl content, Low O and S help offset this some, but data from nuclear power applications show that even with ppb levels of O and S, and <5ppm Cl you can get Cl stress cracking. A clean system helps though. Almost every case that I know of where there was cracking in 'clean' system there were areas that trapped impurities.
Temperature is the big driver. Even small increases in temperature can have a very big impact on CSCC. We all know tales of equipment that ran fine for years, but when the process temp was raised slightly it went to pieces.

If you are in a low Cl, low O, low temp environment it is reasonable to expect low risk of CSCC in a 300 series stainless. If you do experience CSCC don't expect envrionmental changes to move you into a safe region.


= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[SMF1964]

The nuclear industry has had some experience with SCC of 304 welds in high-purity, high temperature water.