MEA corrosion

[tarojm]

We have recentely faced with a sever corrosion of Lean/ rich MEA exhanger tubes in our ammonia plant wich led us to shut down of the plant.corrosion of tubes were in rich side and in the area of tubes located in the tube sheet.Tube material was S/S 304.Any comments with respect to the mechnism of corrosion and the way to reduce it will be appreciated.
masoud

 

[EdStainless]

Was the rich MEA shell side or tube side?
Is the corrosion pitting or cracking?
Are the failures all throught the section in the tubesheet, or only at one end?
What material is the tubesheet?
This should get us started.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[tarojm]

Rich MEA is on the tube side and lean MEA in shell side.Corrosion was in the form of severe pitting.The condition of tubes were good in lean side and the corrosion in rich side confind to the area which the tubes are in tube sheets (in inlet and outlet tube sheet).Material of tubes and tubesheets are S/S 304 but shell is carbon steel.
we have two rich/lean exchangers in series A and B .They are two pass and floating head typ excahngers.The failure occured in the second exchanger espacially in the inlet and outlet side of second pass.Operating condition of them are as follow:
shell side tube side
inlet / outlet inlet / outlet
B PH \T(c) 7.3\104 8.4\86 \63 7.6\74
A PH \T(C) 5.9\128 7.3\104 7.6\74 6.7\100

masoud

 

[EdStainless]

Not where I was expecting it.
Oh well, what else is new?

Were both exchangers built and installed together? Were they built in the same shop? Do they have identical tubes (same mfg)?

Is all of the corrosion is the areas where the tubes were roller expanded into the tubesheet?

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

Here are few things that ate our lunch on an old Girbitol Mea Unit on Low Pressure H2 plant.
Small air leakage on pump seals can be a big problem.
We used a mechanical filter (Cuno)prior to the carbon towers.
You have to have carbon towers (twin) with the proper grade carbon (liquid/liquid). Using 3-way valves, one was always on line.
We used an antifoam, not a silicone. If I remember correctly it was an "Igepal".
All our exchangers were 316 SS shell and tubes.

The main thing that helped alleviate the corrosion problem and pluggage of the HE's was a midnight redesign project of the tube layout on one HE. The existing tube bundles were on a triangular pitch with all the possible tubes you could cram into a tubesheet. We built our own tube bundles and as we had gone through all the permutations of tube materials and sizes, etc. The problem was that with a triangular pitch which made it impossible to clean the bundles or them to stay clean for any length of time. Myself and the fab shop technician decided to build a square pitch bundle for one of the worst offenders. It was built and installed and after 6 months was pulled and no corrosion nor fouling, the tubes were shinny. We got caught during startup by a sharp process engineer who had been assigned to find out why one E-7 bundle on one train was working like a champ and the E-7 in an identical system wasn't doing well. What we lost in theoretical heat transfer, we more than gained in operational performance.
All of the troublesome bundles were changed to square pitch within 6 months and all ran for 2.5 years until the plants were replaced by a single H2 plant with a PSA purification system.

 

[tarojm]

Both exchangers were built and put in service more than nine years ago.They built in the same shop and have identical tubes.Be inform that that these exchanger tubes are in series and the one that have problem is the exchangr with higher rich MEA temperature.The corroded area is only confind to the inlet and outlet tube sheets.The other parts of the tubes are in good condition.

 

[EdStainless]

tarojm,
How long has this corrosion be going on? Was this noticed years ago and has slowly gotten worse? Or has this heat exchanger looked fine and then suddenly pitted?
Have the tubes ever been re-rolled to seal them better in the tubesheets?
I know that most likely no one knows, but this sure sounds like the tube sheet of that HX is running a lot hotter than it used to.
Pitting corrosion in 316 is fast. If there were defects from fabrication they should have failed in months, not years.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[tarojm]

EdStainless,
The faiuled exchanger has been in service in good condition scince one month ago.Ten days later the plant shut downed and the exchenger opened for inspection. During inspection we found that most of the tubes had corroded in inlet and outlet tubesheets.The tubes rolled and expanded in the tube sheet only during shop fabrication.The photoes of faiuled tubes are available and can be sent by e-mail.
masoud

 

[EdStainless]

There was a change in service conditions. You need to find out what it was. I am guessing that the exchanger began running hotter than it had been. Check the flows and temperatures.

Was this heat exchanger cleaned recently?

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[flames]

Check with a process engineer and understand the rich loading and if two phase flow is developing across the exchanger. It wouldn't be uncommon to develop two phase flow on the rich side of the exchanger as the amine is heating up and there is a typical pressure drop across the exchanger. The flashing could possibly lead to an erosion issue and the development of a gas phase (overall a volume gain) can increase your local velocities and flow patterns. The corrosion pattern should also reflect a slight flow tendency so if there is no indication of flow indication of the corrosion damage than this likely isn't the case. If it is you may want to check downstream piping especially around flow disruptions like welds, thermowells, downstream of a control valve, etc.