304L Corrosion

[timMechEng]

I have some air distribution nozzles constructed of 304L for a fluidized bed that have begun to show significant corrosion. We have seen a loss an average of 0.14" of material on a 1.31" OD nozzle. Metal losses come off in small flakes. The corrosion is fairly localized to a 2-3" band. This band happens to be where extra machining and wire-brushing has been performed, but also sees the most potential for higher temp and abrasion.

Could this much material loss be due to lack of passivation or a fabricator being unscrupulous in his use of carbon steel bits and wire brushes, or is it likely due to a different phenomenon? Thanks for the input.

 

[TVP]

Can you post a picture of the nozzles showing the problem area? It is difficult to ascertain whether or not this is corrosion, wear/abrasion, or a combination of both. If the nozzle part drawing does not specifically call out passivation, then I would assume it was not performed. What kind of temperature do you think this part is exposed to? 500 C? 800 C? Based on your description so far I am inclined to believe wear at elevated temperature is a problem, not necessarily corrosion.

 

[metengr]

As TVP pointed out a picture is worth more than words. What concerns me is that the flakes you are observing could indeed be oxide exfoliation. I have seen significant oxide exfoliation of 304 and 316 tube ID surfaces in elevated temperature service (normally service associated with large temperature gradients and a steam environment at 1100 deg F).

 

[Neubaten]

Sounds like the mix of fretting corrosion (corrosion increasing wear, wear increasing exposed surface and thus increasing further corrosion) and high temperature oxidation, but as others said, without a deeper view, it's just a work of guess.