I am specifying Stainless steel grade 304 for a product that will be used in harsh environment. I would like to passivate to improve corrosion protection. What "grade" of passivation should I specify on the engineering drawing? Are there actually grades of passivation? Just saying "Finish: Passivated" seems a bit general to me. There's lots of info out there, but I'm a bit confused. Can anyone offer some straightforward guidelines? Thanks in advance.
Aknotley , We made Stainless steel grade SUS304 for a stamping metal before, that be used in mobile telephone. It is required to exhibit a specified number of "hours to failures" in the salt spray test. For "grade" of passivation, you could use the salt spray test. The salt spray test include Neutral Salt Spray Test(NSS), ASS , CASS. Through the years, there have been some new twists added to better simulate special environmental conditions, but the most common procedure by far is the test as described in ASTM B 117 Standard Practice for Operating Salt Spray Apparatus. Hope it would be helpful for you.
AK, I made a biomass stove (i.e. one that uses partially and fully dried broken wooden twig and other combustible debris) many years ago, from SS304, for use in rural emerging markets (India/ Africa/ Philippines). I had the outside powder coated to give it a nice appearance and the innerwall was native cold rolled SS304 sheet. Within a few days, I noticed corrosion on the inner wall. At 600degC+ the bio mass were pushing out something toxic to man and material. Unfortunately we were far removed from a lab environment, both by geography and by funds/ resources, so we never got to find out why it happened. As a result we never progressed beyond the prototype. About that time BP released a fan based biomass stove, where they supplied processed pellets which burnt cleanly under forced air (from the fan). No corrosion issue there on a similar material, possibly with no passivation. I'd be interested in knowing what passivation processes you are using and if they can take high temperatures as well.
ASTM A967 05e2 (http://www.techstreet.com/standards/AST ... id=1680028) for commercial uses and AMS2700C or AMS-QQ-P-35 for aerospace demands. All reference sources go back to ASTM or SAE and charge for the specifications. Most "Plating Vendors" have copies so work with them to find or develop what will meet your specific needs. Also, consider 316 for these more harsh requirements. If applicable, the longer life you'll get from 316 will more than offset the cost delta.
First of all it depends on what kind of harsh environment, but generally you wouldnt use 304 stainless, you would use 316L and it would be electropolished. We use a company called Anapol (based in digbeth, Birmingham, www.anopol.co.uk). The electropolishing leaves the surface with a chromium rich content which is inert and therefore passive. Phone and ask for advice, but make sure you know the type of hazard in the environment. Any questions just ask! 2Dand3D
