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Activated Carbon heavily pitting stainless steel

Q. My name is Jeff Spooner and I co-own a mechanical seal manufacturing and repair facility in Vermont. Most of the seal applications we see here are process fluids in centrifugal pumps in which a 300 series stainless steel holds up very well. Occasional tough applications require Hastelloy C or titanium but certainly not the norm. We recently began manufacturing a valve seal that works in powdered applications such as cement and 304 stainless steel has been the material of choice. Now this same seal has been installed into an activated carbon powder and the 304 stainless steel is being heavily pitted in 2 months or less. The pitting is concentrated under a lip seal where grease is present and this pitting is causing the lip seal to fail and then compromise a secondary mechanical seal and roller bearing. We are looking for a material to make this part from that will increase life to 12-18 months or longer without increasing cost substantially. A stainless steel is not necessary we could use a strong plastic, bronze maybe even carbon steel as we are mainly concerned with rusting at atmosphere and not overly concerned with product contamination. 2205 duplex stainless has been recommended without explanation and is also quite expensive compared to 304 stainless. Has anyone had similar problems with activated carbon or any suggestions on how to address our problem?

Jeff Spooner
Product Designer - Colchester, Vermont, USA
January 13, 2010

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A. Remember that activated carbon may contain residues of strong chemicals (acids) that are impregnated during its manufacture. Carbon has the highest galvanic potential of all conducting materials. In presence of humidity it will tend to corrode most ANY metallic surface. Look for a non-conductive and corrosion resistant material or coating for your valve, like plastic, or graphite itself. Guillermo Marrufo Monterrey, NL, Mexico January 18, 2010 A. You are more than likely getting galvanic corrosion between the carbon and the stainless. I can't honestly say that I have experience with this directly but I am used to working with carbon fibre. Titanium or Monels are commonly used in contact with carbon to prevent galvanic corrosion. You mentioned you already use titanium on some applications. That would be my first option if you are used to using it. Ciaron Murphy Aerospace - South Wales, UK January 19, 2010

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Can Activated Carbon cause corrosion in 316SS

Q. We are observing corrosion in 316 SS vessel that is used to mix activated carbon and acetone ⇦this on eBay or Amazon [affil links] Warning! highly Flammable! . I expect trace levels of water (<0.3%) in the acetone and the activated carbon will have trace (<.1 ppm) chlorides. The corrosion appears to be only in the bottom dish of the vessel and not the sides. Any idea on root cause? Could it be a galvanic phenomena?

Jim Makuc
engineer - Billerica, Massachusetts, USA
November 6, 2015