Problem With Corrosion Of Stainless Steel

[Martin DowingParticipant @martindowing58466]

Posted by Samsaranda on 10/03/2018 19:59:56:

Bob, you state that customer is a nuclear power station, one would assume that they know their metallurgy and would have specified accordingly, if they are of the opinion that 400 grade “stainless” is not going to rust then they are either deluded or have made a major error in specification. I have worked in companies who contract supply to nuclear customers and my experience is that they are meticulous in specifying materials and processes…

…..If this is an error on their part then one wonders how many other components, perhaps critical components, have also suffered from specification errors.

Dave W

Most of peoples who knew what they are doing are now retired.

Lets hope, nothing will go pop!

Martin

[Clive HartlandParticipant @clivehartland94829]

I think that the washing up liquid is thickened with salt? There must be a better de-greaser for that job?

Clive

[Bob RodgersonParticipant @bobrodgerson97362]

Hi all,

thanks for responding. I have heat treated 10 buttons tonight and will see if this improves their corrosion resistance.,

The same material has been used in the past for this application but nobody can tell us what surface treatment was used ,if any.

I should point out that I am not dealing directly with the power station but with a sub contractor who specified the material. I m trying my best to resolve the problem for him because it has cost him so much money with people being pulled off the job twice while the problem was investigated.

[Raymond AndersonParticipant @raymondanderson34407]

Bob, Would be best if the company involved in the Specs contacted AALCO or James Duva as they have specialist Nuclear / Power Generation materials divisions. and full traceability.

Cheers.

[Ian S CParticipant @iansc]

Perhaps steel(stainless or not) is not the correct metal in this case, nickle alloy as used in our 20C and 50C coins, and "silver" coins in other parts of the world are highly magnetic, but don't become magnetised, they don't corrode.

Ian S C

[SillyOldDufferModerator @sillyoldduffer]

Bearing in mind I know little about stainless I think the thread contains the answers. A few observations:

• The use of the disks in a Nuclear Power Station is a red-herring. They are not part of the nuclear installation.
• 'Stainless', 'Rustless' and 'Inox' are advertising blurb rather than material specifications. They indicate that an alloy is more-or-less resistant to corrosion.
• Stainless steel generally resists corrosion because of the presence of Chromium Oxide. This exists at surface and within the microstructure of the alloy where it protects the chemically active iron.
• Machining stainless is liable to damage the surface and, if HSS tooling was used, to leave scrapings of unprotected iron across and into the surface.
• A damaged and contaminated surface is much more vulnerable to corrosion. Once started this can eat into the iron creating unslightly stains and pin-holes.
• Many varieties of stainless do not resist Chloride ions – salt will attack them.

I think Bob is on the receiving end of unlucky circumstances. The discs:

• aren't made of the most suitable alloy
• have been machined twice, the second time to remove the pip.
• were fully de-greased removing any oily protection and leaving open pores in the metal
• but, the de-greaser contained salt that penetrated into the pores and surface scratches. (Salt is very difficult to remove by cleaning.)
• may not have been dried out sufficiently. And even if they were unrefined salt absorbs water from the air.

I'd suggest:

• skim off or sand-blast the corroded and contaminated layer.
• Polish to reduce scratches and close pores. (As the contaminated layer will be thin, skim-polish might well be the same operation.)
• degrease with degreasing fluid rather than a domestic detergent
• Possibly passivate the surface with an acid ( Citric?)
• Wipe off and dry carefully.
• Package in sealed plastic with anti-rust paper. The paper will deposit a protective layer on the surface and fill pores.

The politics of this may be more important than who was at fault. The customer won't be happy if a second batch goes rusty! If a long-term reputation is at stake might be better to bite the bullet and make a second set.

Dave

[pgk pgkParticipant @pgkpgk17461]

I had a dig about on the web and stumbled across this:

**LINK**

I havent read it all but It doesn't look promising as page 13 shows their best attempts lasted 250 days.

I'd suggest time to rethink the project – perhaps soemething as simple as embedding a magnet in plastic or painting the current items.

[John OlsenParticipant @johnolsen79199]

One thing that does not seem to have been mentioned is the effect of using tooling for stainless that has previously been used for ordinary steels. This can contaminate the surface of the stainless with the other steel, giving a place for corrosion to start. It is especially a problem with abrasives, eg grinders and linishers, where a separate wheel or belt should be kept for stainless work. Obviously cutting tools are less able to transfer contamination but ideally separate ones would still be used.

Incidentally if you visit the gents in places that do a lot of steel work, you will often find that the stainless steel urinal is pitted and streaked with rust. This is from particles of steel that have been carried through on clothing and dislodged onto the stainless. A particle of steel sitting on the surface is enough to initiate corrosion.

John

[Clive BParticipant @cliveb55652]

Bob,

I am sure that passivation will help. If you want to try it yourself, there is an easy to follow guide on passivating stainless steels using a citric acid/caustic soda (sodium hydroxide) three step process. I used this to passivate 303 stainless (another free machining grade containing sulphur) for some components for my home brew boiler/mash tun, Not seen any corrosion – although I know that doesn't prove anything!

Exposed sulphides in FM grades can act as initiation sites for corrosion (apparently, according to the article) and the citric acid must be removing the sulphur as you can smell it (hence the need for a final rinse in caustic).

https://www.cartech.com/en/alloy-techzone/technical-information/manufacturing-guides/how-to-passivate-stainless-steel-parts

Regards,

Clive

[CHARLES lipscombeParticipant @charleslipscombe16059]

This is not directly related to the previous postings but is related to the thread title

I make stainless motorcycle control levers etc from 303-grade in the obsolete patterns used by veteran and vintage m/c enthusiasts.

After polishing the levers the crevices etc usually contain unsightly deposits of polishing soap. I clean up the castings by placing them in a Lidl ultrasonic cleaner with warm water and a generous dose of washing up liquid which does the job nicely. I then rinse the parts in water, leave to dry, then bag up.

Is it fact or urban myth that washing up liquids contain salt? I have never seen or had reported a case of corrosion on my levers etc. I think it very unlikely that the washing up liquids available in Australia are different to those used in the rest of the world.

I have seen adverts for cleaning solutions for ultrasonic baths but does anyone know what these contain and weather they would cause an explosion/fire risk used in a (pretty basic!) Lidl bath?

Chas

[Clive HartlandParticipant @clivehartland94829]

You should not use volatiles in an Ultrasonic, but, you can use a smaller container for tiddly parts but make sure you do not contaminate the liquid.

At this time it is best to use Aqueous solutions and once again I will give you a name,' Micro' which is used by the US Nuclear industry and is only a 2% solution so it last ages.

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