Corrosion Problem in Residue Hydrocracking Unit

znpyro

What was the pH in the overheads accumulator, Monel is susceptible to increase corrosion rates at elevated pH. Was the system fouled , i.e. evidence of under deposit corrosion or was this clean dissolution. Also has there been any significant change in the feed characteristics over the period of problems.

Overheads can be protected from corrosion by a combination of acid neutaliser amines and surface filming chemistries but it is important to identify and control extreme operational situations that can lead

Dear Ron55,

I have not information about the pH level. (I have only half informations, I am not in direct connection with RHCU guys.)

You could see few pictures from monel trays if follow the next link:

http://znpyro.uw.hu/cr4/CR4_picture.html

(sorry for the pop-up windows)

They used neutralizer and filming inhibitors (Nalco made) befor 2005, but our company made a money saver project in 2005 and stoped the adding of neutralizer chemical in RHCU. (And I am afraid of they worked lower dose of filming inhibitor.)

Do you have information where can I find more detail about monel400 alloy corrosion behavior?

Thanks your answer!

Best wihses,

Tibor Nagy

Inhibitors work well, but only when used in correct proportions. Reducing or increasing the amount of inhibitor in a system can drasticly increase corrosion rates.

Was the units grounding damaged? usually if you see a change from normal to destroyed the units earth ground has been damaged.

I think no, becouse only a part of the tower have been corroded. (on upper side of the tower).

From the pictures, I saw the corrosion occurred only to monel 400 trays, and the shell cladded with the same monel 400 have no corrosion. If both the trays and shell cladding have the same material, I think the same corrosion shall be happened for both.

May be :

1. There is a problem with the material of trays, may be out of specs.

2. There is a patch of crude oil with higher H₂S.

3. There is insufficient dose of inhibitor or there no dosing completely.

I made a lot of designs for distillation towers for oil refining cladded with Nickel-Copper Alloy ASME SB-127 (UNSN04400) and still in service up till now since 10^s of years.

Any high temperature excursions between the last inspection period and the failure? Believe Monel more prone to attack (at least by Cl) at elevated temperatures.