coating for caustic storage tanks/pipes 1

[nuig]

Hello all,

Just a quick one I feel. I'm designing a caustic scrubber and I would some info on suitable coatings that's typically used to protect metals any other materials against caustic corrosion.

Thanking you in advance..

 

[kenvlach]

Forget about coatings (except for painting the exterior), only use compatible materials. Visit some scrubbers. You will see white deposits evrywhere -- caustic wicks through valve stems, up tank walls, from pipes, etc. It absorbs CO2 from air, then dries and becomes abrasive. Make everything so it can be hosed down periodically.

I have seen caustic scrubbers with up to 60 HP fans and every one was PVC or FRP for body and tanks. PVC pumps, piping, valves and nozzles. Except, cast iron drive pumps for really large units.

In the metal finishing business, mild steel tanks are used for hot caustic solutions. I think the traditional reason for not using sheet steel for scrubbers was that the caustic would eat through the paint, and when cleaned, rust. Maybe a contributing factor is that commercial caustic soda contains pretty much (0.5% NaCl). However, with better paints nowadays, a good epoxy paint should work.

304 SS is usually used for fasteners. Expensive stuff like Ti works great, too.

Don't even think about using non-ferrous Al, Cu, Mg, Zn or alloys thereof (including galvanize) anywhere. Massive corrosion.

If you don't have a good corrosion book, all of the pump manufacturers have chemical compatability charts. There is a decent one in the back of the Grainger catalog, and Harrington Plastics has one on-line but with less data:

http://www.harringtonplastics.com/

 

[MJCronin]

nuig,

There is information on material selection for caustic systems on the following:

http://www.hghouston.com/naoh_gph.html

http://www.hghouston.com/x/20.html

http://www.corrosionsource.com/technicallibrary/nidi/literature/literature9.htm

http://www.eng-tips.com/gviewthread.cfm/lev2/7/lev3/37/pid/135/qid/23683

Let us know how you make out......

Please post again with information of your final decision..

MJC

http://www.tipmaster.com/includes/refinfo.cfm?w=450&h=350')

 

[kenvlach]

To obtain literature from the CorrosionSource link above requires a paid subscription. You can get NiDI papers on corrosion for free by going directly to the source:

http://www.nidi.org/index.cfm/ci_id/6648/la_id/1.htm

 

[nuig]

Dear all,

FRP is my prefered option for tankage and storage. PVC for pipes.

Thanks for all the really helpful links.

 

[AUSLK]

nuig,
What convinced you to use FRP/PVC? Any technical data from vendors/manufacturers to support your decision that is available for others to reference?

Thanks