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"Rusting on Passivated A304 Steel in Salt Spray Test"
AISI 304 STAINLESS STEEL WHEN TESTED FOR SALT SPRAY TEST FOR 96 HRS HAS RUSTING ON THE THREADS .
PL. ADVISE :
1. How many Hrs. 304 SS can withstand Salt Spray Test.
2. Is the test to be carried as per ASTM B117 [affil. link to spec at Techstreet] .
3. What is the proper process of Passivation with Nitric Acid for Stainless Steel 304 Threaded parts.
4. Can AISI 304 Stainless Steel be used as equivalent to DIN 17440 Grade 1.4301.Sunil Gupta
- Calcutta ( West Bengal) India
If your SS parts are showing red rust they are not Stainless, or they are not 304 stainless.
Stainless steel corrodes almost instantly, but it quickly builds an insulating layer of corrosion that insulates the underlying material. Passivation with Nitric Acid simply forms a very thin, very complete layer which is fairly durable and will protect the surface. As for your questions, here goes:
#1 The number of hours depends entirely on your definition of failure, ASTM B-117 does not define failure for you.
#2 What test? ASTM B-117 is simply a test method, it must be specified somewhere as "the" test method to be used, or it is simply another assumption.
#3 I've always used 20% Nitric Acid in water and about 30 seconds to five minutes immersion depending on the part. I'm sure there are better methods, most of which use citric acid nowadays.
#4 Don't know
Hope this helps, your best bet is to get an expert into your plant to help you set up a process that will work. Consultants are cheap compared to trial and error.
- Pearland, Texas