Why does 304 stainless steel rust

Chloride ions are present during use, causing the surface to be damaged!!

All stainless steels will rust; it’s just a matter of how long it takes or the environmental conditions.

It might be iron ion contamination, caused by stainless steel and carbon steel being stored together.

In corrosive environments, any material will rust； Another reason is that nickel prices were very high in the previous two years; there were many substandard stainless steel products on the market with extremely low nickel content. Unfortunately, if a composition analysis is not conducted during testing, such issues cannot be detected.

Stainless steel 304 does not rust. In my opinion, rusting of stainless steel occurs when it comes into contact with water or steam containing iron ions; in fact, the rust forms on the surface of the stainless steel.

In the production process of stainless steel, this is caused by an excessive amount of ferrite, or it may result from mixing it with carbon steel materials.

There are many reasons why stainless steel rusts: for example, scratches caused by contact with carbon steel, which allow iron ions to accumulate in those scratches (such as during rolling of sheets or handling with forklifts)； Scalding of the stainless steel surface caused by metal spatter during plasma cutting or welding ； There’s also what the original poster mentioned above. The problem can be solved by polishing; pickling and passivation do not work well. In the future, when asking similar questions, please write a few more words to provide clarification. Example: Why do the stainless steel sheets purchased by our company develop issues such as local rusting, widespread rusting, or rusting at scratches (during storage, while being used in manufacturing equipment, after being used by customers, etc.), even though the material tests show they are of Qualified quality?

It may have been contaminated during storage or transportation; stainless steel requires a high level of cleanliness in its surrounding environment

In what environment is the stainless steel pipe used by the poster? Could you explain it in detail so that we can discuss it together! We specialize in stainless steel pipes, and we hope to be able to help you with your questions!

Is there some kind of contact with carbon steel?

Iron ion contamination: Stainless steel should be stored, transported, and manufactured in areas separate from carbon steel； At the same time, protective measures must be in place to prevent surface damage from destroying the protective layer. Most stainless steel equipment is pickled and passivated after being manufactured, and tested using the blue spot method

304 stainless steel can rust, mainly due to chloride corrosion; the resulting rust adheres to its surface

After being manufactured, stainless steel products need to undergo acid washing and passivation to form a layer on their surface that serves as a protective coating.

It’s probably because the surface hasn’t been passivated