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Source of Corrosion on Cast 316 Stainless Steel Valve

Source of Corrosion on Cast 316 Stainless Steel Valve

Source of Corrosion on Cast 316 Stainless Steel Valve

We have a 10" rotary valve that handles a dry pharmaceutical solid.  The valve body is cast 316 SS and the rotor is 304 SS.  

We have seen surface corrosion on the interior surfaces of the valve inlet.  It almost looks as if that portion of valve body is carbon steel clad with 316 SS.  The rest of the valve body (rotor chamber, flanges and outlet interior surfaces) and the rotor itself are pristine. The 316 SS Equipment immediately upstream and downstream of the valve are also corrosion free.

What could be the reasons for this local corrosion?  Why would it not appear on other areas of the Valve? Is it possible that something went wrong during the casting of the valve?

RE: Source of Corrosion on Cast 316 Stainless Steel Valve

The casting may conform to CF8M grade,however while processing there can be contamination in the cleaning area,wrong use of welding rod grade to upgrade the casting or some steel shots dust getting lodged.

RE: Source of Corrosion on Cast 316 Stainless Steel Valve

Could you possibly post a picture of the area of concern?

We have better than a hundred rotary valves at our site and it has been our experience that the body castings haven't been the prettiest especially in the throat area near the flanges.
The problem is mainly shrinkage in this area and usually has the appearance of "mud cracking" This can be very light or in the form of canyons and rivers. The irony of this that one of the better operation rotary valves has the worst problem.  

RE: Source of Corrosion on Cast 316 Stainless Steel Valve

There are cases where casting 'issues' and decreased corrosion resistance go together.  There are also many cases where localized corrosion problems are not a result of casting problems.  Don't get too hung up on connecting the two.  You really need to analyze the corrosion.  It doesn't surprize me that the lines look fine.  The castings often have measurably lower corrosion resistance compared to wrought products.
Look into what else is different in that location. Little things such as temperature, moisture, airflow can really add up to change the local conditions.

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RE: Source of Corrosion on Cast 316 Stainless Steel Valve

Corrosion resistance of 300 series SS castings can be enhanced by proper heat treatment.  Maybe your part did not receive the proper heat treatment and the other parts did get the proper heat treatment.

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