Corrosion on Alloy 400 quill

[rscosta1976]

Good morning,

Please share your experiences with Alloy 400 quill corrosion used to inject caustic upstream CDU charge heater. NACE publication 34101 (2001) refers in 10.4.3 that Alloy 400 may suffer from accelerated Sulfidation corrosion at this location. On the other hand, Nace publication 34019 (2009) refers that materials such as Alloy 400 or Alloy 625 have been successfully for injection quills used for caustic blending at high temperature - immediately upstream CDU charge heater (520F - 550F).

Regardless of the discussion about the location of caustic injection being proper or not (immediately downstream desalter vs immediately upstream charge heater), I would appreciate your thoughts and experiences with Alloy 400 quills sulfidation used for caustic injection at elevated temperatures.

Thanks

 

[cap1a79]

Note that NACE PAPER NO 34109 is not related to CDU charge heater. Referring to the title of the paper, it is NACE Publication 34109-2009, Crude Distillation Unit—Distillation "Tower Overhead" System Corrosion"

Generally, temperature at CDU Tower overhead is not more than 500F. Hence, it is outside of sulfidation.

Regarding your application of alloy 400 for caustic injection quill, I would raise up two points as below.

i) Note that any remaining amount of caustic(which does not react with acid) will possibly induce Caustic SCC for the downstream, especially around preheat & furnace. Check whether it can possibly belong to the zone of caustic SCC based on NACE soda chart for the down stream material (ex., CS, LAS and stainless steel). If yes, the injection point is recommended at CDU overhead, instead. Referring to API 571, process flow diagram, the caustic injection before atmospheric tower is given as "optional" due to the reason.

ii) Sulfidation issue for the injection quill - The resistance of sulfidation is governed by "Cr" contents of the material. Note that alloy 400 (N04400) is the one combined Ni(63% min) and copper(28-34%), Not Cr content mostly.




SiHyoung Lee