Va/Na corrosion on SS 321 tubes

[Nagara]

Hello...I have a furnace that heats a stream of hydrogen, h2s,and heavy naphta from 320 to 380 °C. The tubes are made of 321 SS. The furnace is prepared to burn fuel oil. However our fuel oil contains now 200 ppm of V and 90 ppm of Na(originally, when the furnace was designed didnt contain V). The question is if vanadium/Na will corrode the ss of the tubes, or if it will affect the expected tube life.

 

[btrueblood]

A furnace (what kind?) with tubes - are these boiler tubes, i.e. arrayed above the fire, or air tubes (aka a home heating furnace), or the fuel lines coming to the burners?

 

[EdStainless]

If these are fired you will have trouble.
What is the ash content of the fuel?
With that Na the ash will stick like mad and the V will lead to serious attack risk.

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Plymouth Tube

 

[Guest102023]

At a high enough temperature (not that high actually), aggressive compounds will form that can flux the surface of many CRAs. A little googling should find you the fluxing temperatures of the various VxOy types, some of which are as low as the 1100'sF IIRC. The temperature of the outer skin of the tubes is the issue, not the internal fluid temperature, but based on fluid temperature of up to 380°C (716°F), I would say you may be headed for problems. Upgrading to something like Incoloy 800 won't buy you much either. You may want to thermocouple a couple of tubes nearest the burners to see what skin temperature you actually have. The proper amount of excess combustion air is also a factor.

A quick and dirty way I have used to diagnose vanadium poisoning is to point my PMI gun at it. If and when you examine tubes in service or after, take extra care with hygiene, because the corrosion products are toxic.