I work for a Pharmaceutical company that will decontaminate its biofermentors with 0.78 Advance cleaning solution at 137 degrees Celsius. The Advance cleaning solution is about 39 % NaOH and there is a chelating agent present. After cleaning the top inside lid of the biofermentor is covered in a reddish rust or rust colored material. The biofermentor tank is 316L stainless steel and only the inside top lid is affected by this cleaning and is not in direct contact on a continues basis as is the rest of the tank which is submerged in the cleaning solution and experiences no rusting. Each time the rusting appears we send the fermentor lid out (the inside only) to be electro-polished. This has happened each time we clean the fermentor. We seem to be losing passivation of the 316L Can you please help us determine what might be causing the rusting?

Mr. Hendrix, here is the same message with additional information: I work for a Pharmaceutical company that will decontaminate its biofermentors with 0.78 Advance cleaning solution at 137 degrees Celsius. The Advance cleaning solution is about 39 % NaOH and there is a chelating agent present. After cleaning the top inside lid of the biofermentor is covered in a reddish rust or rust colored material. The biofermentor tank is 316L stainless steel and only the inside top lid is affected by this cleaning and is not in direct contact on a continues basis as is the rest of the tank which is submerged in the cleaning solution and experiences no rusting. Each time the rusting appears we send the fermentor lid out (the inside only) to be electro-polished. This has happened each time we clean the fermentor. Connected to the inside of the lid is a shaft that is about 3 feet long through which plant steam is used to heat the system (cleaning solution). The first 3/4' head of the shaft is a wider in diameter then the rest of the shaft. The head of the shaft is really two pieces held together with 316L bolts but the joint is a Tungsten and Graphite interface and it is at the interface that there seems to be depositing of rust on the rest of the inside lid. We seem to be losing passivation of the 316L Can you please help us determine what might be causing the rusting? Is there some kind of Galvanic corrosion happening between the 316L and Tungsten?