Minimum Cl for pitting of 316 stainless steel?

[CdotS]

What is the minimum chlorine or chloride ion content in ppm in solution to make 316 stainless steel to corrode (especially by pitting) at around 100degree C? Where can I get such information?
Thanks in advance.

 

[stanier]

check out the

http://www.nidi.org

site and go from there. Sharing knowledge is a way to immortality

 

[ijzer]

See e.g. data published by Sandvic and other stainless steel suppliers.
For 316 at 100 Deg. C even 0.5 ppm CL- would be sufficient to create pitting.

 

[Metalguy]

I have see published papers which indicate that ~60 PPM Cl will pit 316 at 100 deg. C, and ~30 PPM for 304.

 

[rolledalloy]

Other concern for any 300 series stainless with even low chlorides and temperatures of 100C is chloride stress corrosion cracking. A duplex such as 2205 might be considered instead, since it is a little better for pitting and is much more resistant to stress corrosion cracking.

 

[bngreene]

I think you may be asking only half a question.

Temperature and initial chloride content are important. However, you must also consider velocity of the process fluid, likelihood of fouling or other deposits to be present, potential for crevice corrosion, possible mechanisms to concentrate chloride ions, and pH.

All of these factors could affect your decision to use 316SS.

 

[NickelMet]

Besides the NiDI site, you can also check out the NACE website for information:

http://www.NACE.org

I can't disagree with what everyone has said previously, especially with BNGREEENE. There are several factors beyond temperature and ppm that are REALLY important, especially those that lead to chloride concentrations within localized corrosion cells. The factors I usually consider: stream chemistry, stream operation (flow), temperature, pH, chloride content, stress, and oxygen presence. All are important and you must consider trends, mins and maxs, etc. when looking at the problem. (We typically try to stay <50ppm for water services at my plant.)

There are different methods to use for prevention and mitigation, depending whether or not your equipment is running or idled. Sources at the NACE and NiDI website are very informative. Above it was mentioned about converting to Duplex 2205. The key word to remember is that duplex is MORE RESISTANT to chlorides, but it is not IMMUNE. Choose your materials wisely as chlorides can attack seemingly (first glance that is) immune alloys. Steels with 8-12% nickel are attacked pretty quickly, while nickel-based alloys with nickel content >45% should be nearly immune. (But, carbon, low alloy, and 400-series stainless steels tend to not be susceptible.)

Sorry for the dissertation, it just happens to be a hot topic here at my plant from time to time. Enjoy, and good luck with your metal.

~NiM

 

[CdotS]

Many thanks for your contribution. Very useful info.