Ok, what is Intergranular corrosion?
Intergranular corrosion is the preferential attack of the grain boundaries within the metal crystal structure. Why does it happen and how can we guard against it?
When stainless steels are heated for between 500 and 800 deg C for a period of time they can become sensitized. Carbon can start to precipitate and joins with chromium to cause chromium carbide precipitation. The net effect once the steel has cooled down is chromium depleted zones in the grain boundaries. This means at those zones the material has lower corrosion resistance. In the right enviroment corrosion can start and propogate through the grain boundries of the steel.
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This typically takes place when welding in the heat affected zones around the weld if the weld has been keep hot for too long.
How do we prevent intergranular corrosion?
By far the easiest method is to control the chemistry of the steel you are welding.
Standard 316 will take approximately one minute of heating into the critical zone to be susceptible to chromium carbide precipitation.
However if you specify 316L low carbon content stainless then it will take 10 minutes approximately to be susceptible chromium carbide precipitation. Since most welded stainless widgets are small and will not be welded for more than 1 or 2 mins selecting 316L is the easiest method to guard against intergranular corrosion.
However, as a consumer you do not control the material selection process.
What else can you do? Heat treatment of parts to redissolve the chromium is an option. But this is not cost effective for a one-off part,
You can follow your washdown/dry proceedure for these parts and do periodic inspection and replacement. If a part shows corrosion on or by a weld replace the part asap.