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How to passify the rusting of a carbon steel flue gas channel?

How to passify the rusting of a carbon steel flue gas channel?

How to passify the rusting of a carbon steel flue gas channel?

(OP)
L.S.,

I am confronted with the problem that rust formation in a flue gas channel in a power plant sometimes results in emission of rust flakes. This is environmentally unacceptable. The flue gas temperature is 150 degrees Celcius in general. The flue gas channel is made of ordinary carbon steel. The rust formation mechanism differs from atmospheric rusting a bit, because the sulphurdioxid in the flue gas lets sulphur penetrate and diffundate through the rust layer to the channel wall. There it seems to perform some katalytic function.
In my urge to prevent this phenomenen coating or changing the channel wall material seem to be the only solutions. I wonder though whether there are no other solutions such as applying some rust inhibiting paint or layer, that slows down or even eliminates the rusting mechanism. I did find some materials like Hammerite and Rust-o-leum. They seem not to be able though to cope with the higher temperature in combination with the presence of sulphur dioxide.
By the way I can state that during normal operation the concentration of sulphuric dioxide is thus low that the dew point temperature is not higher than the flue gas temperature.

Through this thread I would like to find out whether there are industrially available paints or coatings that not only separate the flue gas atmosphere from the channel wall, but also actively passify the rust mechanism. I am thankfull for any suggestions.


With best regards,

Karel Postulart

Karel Postulart, The Netherlands
Nuon Power Generation

RE: How to passify the rusting of a carbon steel flue gas channel?

Consider internally coating with high temp epoxies (like FX-464 Novolac Epoxy)

Surfaces Blasted to SP-5 White Metal Finish
Coating Applied Before Any Rust Blumes
Work Area Free of Airborne Dust
Brush, Roller or Spray; 10 Mils per Coat
Mix Part A and Part B (50% each)
Apply 2 Coats

RE: How to passify the rusting of a carbon steel flue gas channel?

Karel,

Dew point corrosion caused by S02/SO3 is a big concern in any power plant. As explained earlier, use of Novolac epoxy is a cost efective option.Adherence of the epoxy will depend a lot on the orginal surface preparation, curing time. Thermal fluctuations during shut downn and start ups could cause flaking of the epoxies.Also the formation of crevices/corossion forming pits can not enitirely minimized with epoxies though could be minimized a lot.

The other option could be to switch to "weathering steels ", e.g corten and similar steels with enhenced resitance to acid gas dew point corrosion.
Some references on such products are as follows:-

- http://www.nssmc.com/en/tech/report/nsc/pdf/n9007....
-http://www.nssmc.com/product/catalog_download/pdf/...
-http://www.nssmc.com/en/tech/report/nsc/pdf/n8703....

Thanks

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299


RE: How to passify the rusting of a carbon steel flue gas channel?

Pradip makes a good point, changing materials would be prefered option.
Any paint coating system depends on the surface prep.

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