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  • Protection for Pitting Corrosion on Welded SS

    Discussion in 'Surface finishes' started by Wmech, May 1, 2013.

    1. Wmech

      Wmech Member

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      Hi, first, i want to say thank you for all the inputs and suggestions from all the professionals on this topic of the surface finishing process.

      Two pieces of 304L Stainless steel sheets are bent and weld together with 316L welding rod. Along the welding part, the Heat Affected Zone (HAZ or heat tint) shows on each part of the welding joints.

      The purpose of the tank is to contain fluids such as domestic water or antifreeze, and heat the fluids up to perform heat transfer as a burner. I understand that antifreeze is highly corrosive especially in high temperature. In our application, the tank reaches as high as 200 F.

      From the first visual inspection, outside surface and welds of the SS sheet metals are fine, when the tank is opened up, the pitting corrosion occurs everywhere along the heat tint. The situation only happens on one tank which is awkward to me.

      In any case, i have looked for some method of preventing pitting corrosion or corrosion in general. The followings suggestions are what i have found with questions:

      • Coating with porcelain or epoxy --> not sure if they can stick with SS at high temperature to prevent the corrosion at the welds
      • Cathode and Anode method --> One of the considerations, however, the life span of this method at high corrosive environment
      • Switch to 316L SS --> it's more expensive and it only last 6 months to 1 year longer than 304L
      • Cleaner welding shield and pickling paste --> not sure if that will restore the micro-structure of the heated SS. Besides, haven't seen any high temperature pickling paste

      That's pretty much it in terms of protection/prevention. I am pretty sure this is not something that is uncommon. Hopefully whoever has experience with this can give me a tip or a guideline. Once again, thank you for your input and support

      Best Regards
       
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    3. jarrjenn

      jarrjenn New Member

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      You did not mention if you were passivating this part after welding. Welding SS causes free iron to remain on the surface, especially on the HAZ as you put it (scaling), which leads to pitting corrosion. Refer to ASTM A380 and A967 for specifics on how to passivate stainless steels.

      JJ


       
    4. Wmech

      Wmech Member

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      Thanks for your reply. We didn't any passivation process on the stainless steel after welding. If that's what you suggest, i will look it up for those two references.

      How about the other alternative that I have mentioned?

      regards
       
    5. jarrjenn

      jarrjenn New Member

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      Passivation is the only method that will return the heat affected area back to its' original level of corrosion protection. I strongly suggest you do this before doing any other method.

       
    6. Wmech

      Wmech Member

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      Thank you for your input and suggestion. I will look up more about the passivation procedure.
       

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