CDU Overhead Condenser Corrosion

[ponderer]

We have a two stages overhead condensation design in our CDU.

The first stage inlet temperature is 150C and outlet temperature is 120C.

The second stage inlet temperature is 118C and outlet temperature is 60C.

The material for these condensers are Carbon Steel.

We encounter serious corrosion in the first stage condenser.

The chloride content in the second stage water boot is around 20~100ppm.

We inject corrosion inhibitor ahead of the first stage condenser and inject wash water/neutralized amine
/corrosion inhibitor ahead of the second stage condenser.

I would like to know any refinery has the same experience as us.

 

[MaNaTMoS]

Dear Ponderer,

there will always be "cold" (local) spots at the inlet of 1st stage condenser, where corrosion will take place, caused by high pH value of so called "first water droplet". To avoid this, continuous waterwash injection point should be moved to the inlet of 1st condenser, at reasonable distance.
Make sure you have good water distribution (nozzles); water direction should be countercurrent to overhead gas direction. If distribution is poor, most likely that you'll have premature corrosion/tube failures.
Consider the possibility to modify condensers construction materials.

From process side of view, you should maximize pumparound duties (circulating refluxes) and unload overhead condensers. Maintain good desalting practice (10ppm chlorides at desalter outlet) and regular reflux drum pH control, once a shift at least.

Best regards,
MaNaTMoS

 

[MaNaTMoS]

Sorry, there was a writing error in the previous post (about "first water dropplet"); I wanted to say - high acidity and LOW pH.

Maybe I just work too much.
)


Regards