316L Reboiler Tube Temperature Discoloration

[rustbuster]

Hello all,
I have some 316L reboiler tubes suffering preferential attack at the baffle locations in an MEA solution. There is also a distinct dis-coloration that appears to be a temperature gradiant in these locations (blue - grey0. Does anyone have an idea of what temperature range this may occur at. Operating at about 300F.

Best Regards. L. Davies

 

[unclesyd]

There are books on MEA/CO2 system corrosion.
Some questions to start with.

Are the baffles S/S?
Could the attack be wear from vibration?
Are the reboilers, separate from the liquid/liquid heat exchangers, fouling?

Get back with this information and there maybe some help.

 

[rustbuster]

unclesyd,

Yes, the baffles are 316. There is evidence of fouling, supspect an under-deposit attack in the crevices. Both tube and baffles corroding with failures after 7 months.

I believe the major issue to be degraded solution however temperature definetly contributes. My question is primarily regarding the temperature range where discoloration is observed. Thanks for your time.

 

[unclesyd]

You are making me think so I may ramble.
We had similar problems in two low pressure Girbatol H2 plants with MEA scrubbing systems. Anywhere we had deposits we had corrosion on the HEs. The corrodent was never identified, but we eliminated this type corrosion to the heat exchangers by the installation of Carbon towers into the system. The carbon was an SGL material. It was installed as a side stream system with a pretty good flow. I don’t remember at what point it was located. I’ll try to find out.

We had the color you mention, variegated blue to purple, on nearly every thing. If I remember it was very intense on the HEs. We never attempted to analyze it as it was deemed harmless.

Our biggest problem was fouling of the Liquid/Liquid exchangers and reboilers very quickly after installation.
The carbon towers helped but didn’t resolve this problem. We were constantly rebuilding these tube bundles in our shop due complete plugging caused by the close tube spacing and the triangular pitch. The man in tube shop and myself solved this problem by sneaking, (midnight plant test) in an tube bundle with 25% less tubes and on a square pitch. The square pitch was for cleaning if necessary.
When both plants were decommissioned 3 years later all exchangers were of this design.

Is the corrosion between the tube and baffle or adjacent to it?
Is this a clean CO2 stream? We used 316S/S or 304 S/S.

 

[rustbuster]

unclesyd,

We are treating an H2S/CO2 gas stream. The corrosion occured between the tube and baffle and may be partially due to movement. More likely acid concentration at the crevice / deposits.

We do have carbon beds in service as well.

 

[unclesyd]

tubI'll have to defer to one of the H2S experts for more insight on that aspect of the corrosion.

If there is any movement in the baffle area it can and will accelerate corrosion by removing any protective film. We had tube bundles where vibration was a problem and had to roll the tubes at the baffles.

Looking at some very old notes there was mention of some problems with the carbon towers. There was a change in carbon type/brand an it resulted in a shorter life of the beds, changing back to the original corrected this problem. The other had to do with operation of towers. No idea of what, but probably not switching them.

If you can give the material specifications for thees, baffles, and shell.