stainless steel grade and welding to carbon steel 1

[ranmoo]

I have a client in an industrial application that is looking to replace a 30 year old conveyor. The conveyor was originally and currently painted carbon steel. The purpose of the conveyor is to move and simultaneously cool portions of tires under their manufacturing process. The cooling is mostly handled by spraying water over the materials as they pass. The water is slightly acidic, and has caused slightly aggressive corrosion in the side and bottom plates and their joints of the conveyor support frame through the years. Annually, portions of the conveyor sides and bottom plates have been replaced or stiffened due to corrosion (with similar carbon steel plates).

The current objective is to replace a significant length of the conveyor. I have been asked to design new side plates and bottoms out of stainless steel, and the load carrying support channels out of painted carbon steel. Other components in the vicinity (catwalks, misc. equipment frames) will be carbon steel as before.

Questions (and I welcome feedback, please):

- what grade of stainless steel is recommended for this application as the side and bottom plates for a conveyor that is exposed to slightly acidic water spray (economics and availability will play a part in the decision as well)?

- The painted carbon steel support channels, other W-shapes in the vicinity, grating, etc. will not be exposed to the acidic water spray. How is the best way to weld carbon steel to the stainless steel plates and their recommended grade? Welding Electrode? Welding process? Are dissimilar metals a concern between the recommended SS grade and A36 carbon steel (that is planned on being painted)??

Thank you

 

[metengr]

What type of water is the client using for spraying? In other words, what is the source of the water? This information would help in evaluating specific materials.

The welding of dissimilar metal welds (CS and austenitic stainless steels) can be done using a 309 filler metal composition, and one of several welding processes - GMAW (MIG), SMAW and FCAW.

 

[ranmoo]

Thanks for the response and appropriate questions ... I contacted the Owner today and he informed me that the water is "Muratic acid and maintain the pH between 6.0 and 7.0".

Hope that helps?

 

[metengr]

Ok, this makes a big difference. Muriatic acid is diluted hydrochloric acid. Conventional austenitic and even duplex stainless steels should not be used, and are not recommended by literature. In this case, you might need stick with a good barrier coating on carbon steel, and forget about stainless steel in this application. I would be concerned with pitting in this intermittent wetting environment.

 

[ranmoo]

do you have some reference materials or websites that I could forward to the clinet, for they are pretty well set on stanless steel.

 

[metengr]

Go here, and find the corrosion tables;

http://www.outokumpu.com/applications/documents/start.asp

 

[EdStainless]

If the pH is clear up at 6 then I am not very concerned. I wouldn't use a 3XX series, but a duplex should be fine. This isn't as acidic as the mine applications or coal handlers.

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