"Oxidation of 316 SS"

Question:

"I would like to better understand the effects of temperature and reduced pressure on oxidation of 316 SS (an other grades of stainless). The process in question involves heating and pulling /forming pyrex glass tubes over a 316SS mandrel. Heating is accomplished by an external resistive heating coil surrounding the outside of the glass. The process is performed at 1500 degrees F at 1x10^-2 Torr. Please detail the extent of oxidation of 316SS at reduced pressure and temperature. The glass is actually in contact with the metal. Will the stainless steel produce an oxide film on the glass? How much will oxidation be reduced by further reducing oxygen concentration (lowering pressure to 10^-4 torr)? What about 10^-6? Should we consider using a different grade given these conditions? What do you recommend. The manufacturer reported a brownnish, film forming on glass which, upon cooling, would harden and flake off. I am faily sure the reported film is carbon soot from a hydrocarbon based lubricant they are using to lubricate the mandrel. The glass requires a cleaning step after the process which they would like to eliminate. They wish to due away with the lubricant and we all would like to better understand how oxidation of stainless steel may be controlled by temperature and reduced pressure (reduced oxygen concentration)."

Answer:

1500F is about the upper limit for type 136SS exposed based on high-temperature oxidation. As the pressure is reduced (increasing vacuum) the oxidation potential should become less, based on reduced availablity of oxygen. Unfortunately, we cannot help quantify the extent of oxidation at different vacuum levels as all the available oxidation data that we have access to is based on exposure to atmospheric pressure.

 

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