You are currently viewing: Q&A

---

---

• We didn’t expect severe corrosion issues in the carbon steel of our amine unit. What is causing it?

  Jun-2021

---

Answers

---

• rajkumar chate, sulzer chemtech Ltd, rajkumar.chate@sulzer.com

  Corrosion in the amine unit is very common. Most common reason for the corrosion is higher amine loading. Check the rich loadings. If it is >0.45 mol acid gas/mol amine then increase the circulation rate. This requires more energy for regeneration but if you are not limited by the lean end pinch then you can allow higher lean loading in lean amine.

   

  Jul-2021

• Celso Pajaro, Sulzer Chemtech, Celso.Pajaro@sulzer.com

  We will provide several potential explanations to the corrosion phenomenon:
  Amine appearance: one indication of corrosion is the increased presence of solids in the amine solution.  Allowing a high solid content in the amine accelerates erosion — corrosion problems as well as will increase fouling problems.  The refiner will need to operate the filters at the maximum flow rate.
  Check filters: take samples of the amine solution upstream and downstream of the filter to verify it is properly working, some filters have had problems with poor sealing that allows unfiltered amine to bypass the filtration element.
  Check the amine appearance of the rich and lean amine, if the rich amine is dirtier (darker) than the lean amine please check the amine quality for:
      -    High CO2 content in lean amine (for units treating streams with H2S and CO2) will keep iron carbonate in solution, and once it enters the amine absorber it will precipitate iron sulphide.  Increasing amine regenerator reboiler duty should reduce CO2 in the lean amine
      -    Another mechanism is the presence of amine degradation compounds that keeps iron soluble until it gets in contact with H2S in the absorber.  There are several public guidelines on the maximum amount of amine degradation products for each type of amine.
      -    o    Excessive acid gas loading in the rich amine.  High acid gas loading produces amine bisulphide that can penetrate the iron sulphide protective layer on the carbon steel and accelerate corrosion.
      -    o    High pipe velocities will produce an erosion-corrosion effect, amine solution velocity in carbon steel piping should be kept 6 ft/s maximum.
      -    o    Two phase flow can also accelerate corrosion in carbon steel piping.  
      Rich amine pipe located downstream of the rich/lean amine heat exchanger should be checked for two phase flow, the rich amine control valve that feeds the regenerator should be as closed as possible to the regenerator inlet.
  -        Rich amine pipe located downstream of the amine contactors control valve should also be checked for two phase flow, it is preferred to have the control valves as closed as possible of the amine flash drum.
      -    Equipment showing signs of corrosion due to wall thickness measurements or visual inspection
      -    o    Amine regenerator acid gas overhead drum.  The presence of ammonium bisulphide or cyanides can penetrate the iron sulphide layer and attack the steel.  An analysis of the reflux will help to determine if there are high concentrations of either component.  If this is a problem, a portion of the reflux should be diverted to a sour water stripper unit.
      -    o    Amine regenerator reboiler.  Poor amine regeneration can increase the acid gas content in the amine going to the reboiler.  Once amine reaches the reboiler it will be heated allowing the release of the acid gas which will produce corrosion.  Taking a sample of the amine before going to the reboiler will indicate if more regeneration is needed.
      -    o    Bottom of amine regenerator.  Poor amine regeneration and high momentum of the vapours (or vapour — liquid) coming from the reboiler can impinge on the vessel wall and remove the protective iron sulphide layer.
      -    o    Amine contactor can suffer from corrosion problems in the bottom due to feed high momentum that impinges on the vessel wall.
      -    o    Any equipment made of carbon steel will suffer from cracking problems if it is not properly processed using the right chemistry, welded properly, checked for hardness and, if required, post weld heat treated.

   

  Jun-2021