Stainless Steel containing NaCl solution

[mead]

Hello,

We have an application at our plant that calls for storage of a product solution that is 18% NaCl at temps up to 70 deg C. Our existing 304L and 316L storage Tanks are exhibiting alot of pitting corrosion. Any thoughts on a good stainless alloy to look at for this application, possibly a duplex? Any good reference sites for corrosion info with stainless would also be appreciated.

 

[mcguire]

This environment will call for the premium stainlesses. You can use either a super austenitic or a super duplex.
You need a PRE ( pitting resistance number) of more then 40 where PRE= %Chromium+ 3.3x%molybdenum + 16x%nitrogen.
The commercial duplex which satisfies this is 2507 ( uns S32750 ). A super austenitic which satisfies the criterion is AL6XN.
Contact Allegheny Ludlum or Avesta/Sheffield for tecnical help. They have interactive web sites.

 

[joeswoes]

Have you considered lining the tank with a plastic, either as a spray dispersion or solid fused lining ? Any plastic would be unaffected by this solution.

 

[Hush]

To add to joeswoes comment, a teflon based coating would also work well. Impreglon is one trade name that comes to mind.

 

[mead]

Does anyone have any practical experience lining an existing tank with teflon, etc.? ANy companies that do this kind of work? This tank is cooled and can go from 0-70 degrees C, any thoughts on if the teflon will expand contract with the tank? Thanks

 

[rustbuster1]

There is no need to specify a "teflon" coating material. Many, more conventional coatings - including epoxies, epoxy novolacs and polyurethanes - will provide the protection you need. These cost about $10/sq. ft. applied. Surface prep can be abrasive blasting to provide an anchor pattern to enhance adhesion. Heavier build trowelled linings are also worth considering - they typically cost about 18-20/ sq.ft. but are more mechanically rugged than thinner coatings. In light of your "thermal shock" possibility, 35 - 45 mils of a premium coating like Plasguard 4550S would be a good choice.
You could also consider cathodically protecting the tank - this is common in pulp and paper mills to prevent pitting and crevice corrosion of stainless steels.

 

[mead]

We are considering an epoxy coating but are a little hesistant because the products stored in the tank are food grade and kosher. That limits the selection of coatings we have been able to find. ANy suggestions would be appreciated.

 

[rustbuster1]

Several epoxy coatings have FDA approval. Contact Don Sampson at STONCOR which covers Plasite coatings. He is in their Maple Shade, NJ office. Try STONCOR on

http://www.google.com