Amine Tower Corrosion

[1906]

We have amine(DEA) tower(Random Packing) in our hydrocracker unit operated around 180 Kg/cm2 and some thickness loss was found at the bottom line of this tower during our T/A period dated July 2005. So,we had changed some demaged part of the bottom rich amine line during T/A and started again. At that time we thought high amine operating temp.(around 85'C) and high H2S load(0.5 ~ 0.6 mol/mol) were among the reason of the corrosion problem. With this regards, we decreased operating temp. to around 70'C and H2S load to 0.4 mol/mol after start-up.
But, after start-up still we have found metal loss in our amine tower bottom elbow area, especially weldseam connecting tower shell to elbow and shell weldseam (above liquid level and below gas inlet line).
WE WONDER WHY STILL CORROSION IS NOT SOLVED IN OUR AMINE TOWER DESPITE OF LOWERING H2S LOAD AND TEMP. IF ANY BODY HAVE COMMENT, PLEASE LET ME INFORMED.

 

[visangio]

Dear Sir,
I think that the most probable reason for corrosion is flashing of H2S. That is typical in absorber bottom and rich line exchanger.
In any case the operating temperature seems to me too high. Normally amine temperature should not excedd 38 °C, in order to optimize abosrption. Gas temperature should be 5 °C lower to minimize the risk of condensation of hydrocarbons.
DEA units should be operated with a maximum H2S load of 0.5 mol/mol, so the new load seems to be OK.
Additionally I recommend to implement the utilization of a proper corrosion inhibitor. Please contact me for further information (vincenzo.sangiorgio@ge.com)
Best regards

Vincenzo Sangiorgio

http://www.gewater.com

 

[0707]

Weld seams of your bottom elbow connecting to tower shell have been PWHT (Post weld heat treated)? Is your elbow material Carbon steel? If so, is your material HIC resistant? Are your Amine filters performing well? Does your operating windows have been modified only by feeling thoughts or through real research? What kind of inhibitor corrosion treatment do you have in your Amine plant? Is it reliable? Did you discuss these matters with your unit licensor?
Try to ask these questions and maybe you will find the answer for your corrosion problem
Regards
Luis Marques

 

[rzrbk]

For the corrosion in the bottom elbow, check the liquid velocity. Rich amine in a carbon steel line should be below ~6 ft/sec.

Not sure on the area above the liquid. I have seen blistering in a carbon steel vessel of this type in that area, but am unsure why it would have more corrosion that the submerged part.

 

[1906]

Re the rzrbk's comment, some paper says 3 ft/sec for amine in carbon steel.
Is there any special reason keeping amine velocity below
6 ft/sec in carbon steel line ?

 

[bspooner]

In our experience 6ft/s is the maximum for rich piping, 3ft/s is the max in certain types of exchanger tubes.

Ben Spooner, P. Eng
Process Engineer
Amine Experts Inc
Calgary, Alberta