Chloride Stress Corrosion Cracking and 316 Stainless Steel

[beh188]

I have been reading into Stress Corrosion Cracking (SCC) caused by chlorides, which I understand can be quite an issue.

Is there anything you can do to 316 stainless steel to make it acceptable for use in a chloride environment, or is it just recomended to avoid 316 stainless steel in this application? Perhaps solution annealing will help put the carbides into solution?

 

[EdStainless]

I has little to do with the carbides.
It has to so with the FCC crystal structure, 10% Ni, and applied stress.
If you keep the stress below about 10ksi (applied + residual) and the temp below 125F then it will not crack.
There is no Cl level low enough to prevent cracking if the temp and stress are high.
Virtually every piece of SS made has residual stress levels that are over 30ksi unless it has been process by special methods.
If SCC is a risk then use a duplex SS. They have significant resistance.
If you really must avoid it then use a ferritic SS. The nickle free BCC alloys will not chloride stress crack.

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Plymouth Tube

 

[SJones]

Some people believe that painting the material is an acceptable corrosion control measure for SCC. Another school of thought is that only thermal spray aluminium is acceptable as a coating. The conditions for SCC are known and if the material is to be exposed to those conditions, and cracking cannot be tolerated, change the material.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[moltenmetal]

Everything EdStainless said is true, and yet 316 SS and even 304SS are still widely used and give acceptable service life in all sorts of services containing chlorides and where temperatures exceed 60 C.

Much depends on whether the source of chloride is external or internal to the pipe. Much also depends on factors which would tend to concentrate chloride i.e. by evaporation. Dissolved oxygen content plays a role in fully immersed services.

 

[EdStainless]

Yes 300 SS is quite useful and is found in many applications where the risk of CSCC would appear to preclude its use.
However, there are many cases of CSCC failures. These range from kitchen appliances to bridges and buildings.

Cyclic heating is usually the worst situation. You can get concentration of chlorides as well as thermal stresses.

You must first have some corrosion before CSCC can happen, so if you are safe from crevice corrosion you should be safe from CSCC.

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Plymouth Tube

 

[blacksmith37]

The best way to prevent Cl SCC of 316 is to relpace it with Incoloy, Inconel, Monel , etc.

 

[EdStainless]

or a duplex SS (all of them are almost identical in SCC resistance), the next step up is a 6%Mo superaustenitic alloys.
Then you move to Ni based alloys.
Remember that Incoloys are just high alloy stainless alloys.
And not all high nickel alloy have good resistance.

Just to keep things in perspective, there are environments that will cause stress corrosion cracking in all alloy systems.

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Plymouth Tube