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a7992 (Industrial) (OP)
11 Mar 09 12:16
We have had some cracking issues (SCC) after we've cleaned our 316SS heat exchanger in the past.  We are looking at cleaning it next week as it is fouled.  Does anyone have any suggestions on caustic to use or not use with 316SS??    
EdStainless (Materials)
11 Mar 09 14:59
Do you have any idea if your cracking was from chlorides or caustic?
I doubt that it was caustic cracking unless these units were poorly washed and then run very hot.
My hunch is that it is trace levels of chlorides that are causing the problems.  Watch out for chlorides in all of the solutions that you use.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

strider6 (Materials)
12 Mar 09 2:42
i agree with Ed about chlorides but depending on concentration and temperature (approx > 80°C) also SS can suffer from caustic stress.

Selection of stainless steels for handling sodium hydroxide (NaOH)
http://www.bssa.org.uk/topics.php?article=34

S

Corrosion Prevention & Corrosion Control
 

tomwalz (Materials)
12 Mar 09 9:14
Use a commercial prep with a heavy rinse agent component.  

 

Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.    

unclesyd (Materials)
12 Mar 09 13:03
tomwalz is on the right track about using a commercial caustic product as they contain all the others need to make and effective caustic cleaner. On thing additional I would check on is the Cl content of any cleaner used as some carry high levels of Cl, comes from the NaOH used.

Could you give a little more information about your process as there are somethings you can do to greatly enhance the cleaning ability of caustic cleaners?

Also there are acidic cleaners that work on some soils and are quite safe on SS.  
EdStainless (Materials)
13 Mar 09 14:28
And check the Cl level on your rinse water.  I am a big fan of less than 2ppm.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

unclesyd (Materials)
13 Mar 09 16:35
EdStainless,

I'm a charter member of that club.  
MikeMet (Chemical)
13 Mar 09 19:34
Depending on the pH of the caustic you can tolerate a lot of chlorides.  I think I have attached a graph that showing results of chloride limits to prevent ClSCC in caustic.   Depending on concentration of caustic and temperatures you can get caustic SCC.   I agree with others that you also have to watch for chlorides in the rinse waters.  A failure characterization would be most helpful in determining if the problem is caustic or chlorides

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