304 Stainless Steel Rusting

We did have a case recently where stainless steel washers from an overseas manufacturer were showing signs of rust. The fault was traced back to the stamping machine which had a worn head, leaving steel particles imbedded in the washers which rusted. This is the only instance I am aware of that would cause stainless steel to exibit signs of rust (wrong material composition seems unlikely to me).

I work for a fabricator that makes only stainless steel equipment, primarily for the pharmaceutical industry. We treat all ss (304 or 316) with at least a bath in a strong nitric acid to remove traces of "free iron". The pharmaceutical industry requires in their project specifications that all tools be proven to not contain any standard carbon steel, and they inspect at times for this. That is indeed a major source of rust on austenitic steels.

Like the previous posts, cross-contamination from tools used on carbon steels is most likely the cause.

All stainless steel is protected by a chromium oxide layer that forms on the surface.If the surface is scratched, and the film does not have time to heal before exposure to certain corrosives, the metal will corrode.I have seen holes in stainless piping due to corrosion when the inside surface was scratched by solids in the pipe while carrying acids and/or caustics.However, I have not see brownish rust streaks except from iron contamination from tooling, etc.

304 stainless steel is subject to pitting corrosion caused by bacteria http://www.nace.org/nacestore/assets/CJAbstracts/04070658.pdf

greetings - 304 is not a particularly good grade of s/steel - 316 would be the go.

If you place a magnet next to 304 there will be some attraction, whereas with 316 there will be no attraction.

We often find 304 rusts in the food industry - we always stipulate 316 for tough areas

Stainless steel are rolled/machined to semi raw material and cross containmination (free iron implemented) take place as mentioned. Free iron is removed and Chromium oxide surface formed when SS surface is passivated thru electropolish. I think this is the root cause. So, engage electropolish supplier for further advice.

We treat all SS with Bradford DeRustIt to remove any tramp steel particals. You can rub a nail on SS and it will rust through at that spot. Galvanic action of two metals. Salt water will speed up the process.

32% Hydrochloric acid will attack SS (any grade including 304) causing it to "rust". Maybe the exposure to salty sea elements is the cause.

Stainless steel doesn't rust under normal conditions. Stainless gets its non corrosive properties from the chromium in the alloy. The chromium atoms combines with oxygen and forms a passive surface film over the base steel very much like the paint protects your car. Once this layer is removed the base metal is exposed to the moisture in the atmosphere and rust forms. Chlorine in any form combines with the chromium and removes this protective layer and exposes the base metal and rust will occur. NEVER use any chemicals that contain chlorine near any stainless. This includes any cleaners, acids to clean quarry tile or brick, and some detergents. Even the vapors can attack stainless steel. The only inorganic acid that is friendly to stainless is nitric and it is used to remove any iron particles left on the surface from manufacturing or machining. Never use steel wool to clean stainless. Particles of the steel wool will get trapped in the grain of the stainless and these steel particles will rust.

I worked with a man for a number of years that would make stainless rust, it did not take long to figure out why our exspensive mics, calibers and pocket scales all made by Starrett of stainless would have finger prints corroded into the surface and some items would turn dark all over. We all quit letting him use our tools and the problem stopped at that point. I still have stainless that has been used for 20 years with his finger prints well defined. Would this be chemical or biological?

This was most likely caused by (imho) cross contamination of the free steel etc... particles transferred from the parts being dimensionally inspected to his skin and then to the measurement gage. Happens all the time in Phys D inspection processes...that is why it is important to keep the Mics and Calipers etc.. cleaned with alcohol and then wiped off and/or oiled after use....

we used 316ss at high temp for process. unfortunately the chlorides in the feed pitted the steel and eventually ate through. we could not change the chlorides but went to a higher grade ss, duplex ss. its been working well. chlorides ate through the nickel, i was told.

Why must the acid used for passivation be inorganic? We used citric acid to passivate the stainless steel sheets used for radiant heating panels as well as other electric heater sheaths. It was quite effective and environmentally "friendly" for health and disposal.

I have seen a chemical offered by Johnson Screens that cleans off the surface corrosion and also repassivates the stainless steel leaving the product looking new.

They can be contacted at 800-833-9473 x-117, they might be able to help.

DOES THE DISCOLORATION APPEAR IN THE HEAT AFFECTED ZONE OF WELDED PARTS?

304 ARE NON-MAGNETIC WHEN ANNEALED BUT CAN BECOME SLIGHTLY MAGNETIC WHEN COLD WORKED. WITH 304 YOU MAY HAVE PROBLEM WITH INTERGRANULAR CORROSION FOLLOWING STRESS RELIEVING OR COLD WORKING.

304L IS MY CHOICE DOES NOT EXHIBIT CORROSION PROBLEMS FOLLOWING STRESS RELIVING OR COLD WORKING.

316 IS MY CHOICE FOR ANY MARINE ATMOSPHERE AND MANY TYPES OF CORROSIVES?

316L IS MY CHOICE IF WELDING WITHOUT BEING ABLE TO ANNEAL THE MATERIAL

STOP SHOUTING!

please give me a call. have big problem with rust and would like to know your thoughtss. 208 354 4747,

thanks ,

steve carlson

304 stainless will indeed rust when exposed to high salt concentrations. We specify 316 stainless for handling salt.

If you have a high chlorine environment 304/316 will experience surface cracking. 400 stainless will be required.

Regards, Delmar Schmidt
Melfi Technologies Houston
www.melfitechnologies.com

Stainless steel corrode due to appling high temperature (550-850 C) and cause intergrauler corrosion due to carbide forming with Cr which lead to decrease the concentration of Cr less than the safety limit (12 %) and so lead to corrosion.

so I think Concern on

1-Service Temperature and time

2-Atmosphere which may be cotain chlorine

3-scrattching of surface

One common form of rust on stainless steel in marine locations is called "tea staining". The Australian Stainless Steel Development Association (ASSDA) has info in the following document: http://www.assda.asn.au/data/portal/00007704/content/61529001145508815004.pdf , and the website is an excellent source of SS info.

304 stainless stell material will rust but 304L will not. 316L the most superior and used for high grade requirement.