corrosion near burner zone of oxidation reactor

[pbrod]

We are facing severe corrosion problems on the wall of 5x5m vent gas duct before an oxidaton catalyst. In this duct one natural gas burner is installed to preheat the air going to the catalyst during startup. The material is HII steel welded on a structure made of metal beams. The sheets are serieusly deformed probably due to mechanical forces of thermal expansion.

More serious is the reduction in wall thickness in the zone around the burner. It looks like the steel suffers from the radiation of the gas flame. The temperatures of the gas is around 470°C during startup and 380°C during service.

Can anyone help with the corrosion mechanism? Is it because the carbon is burned out of the metal structure? Anyone suggestions for a good suitable material for repair?

Thanks in advance!!

 

[EdStainless]

Most likely a combination of oxidation and thermal fatigue. Every cycle causes spalling of the oxide which accelerates the metal loss.
You could slow this down using a high Cr steel (2.5%-5% Cr) or use some 304 SS sheet in these areas. They will still deform (you want that, otherwise something will tear) but greatly slow metal loss.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metengr]

Most likely exposure to radiant heat, similar to flame impingement, is causing excessive high temperature oxidation of the steel. I would use a ferritic stainless steel for the ductwork, like Type 439 to avoid excessive warpage.