Rusting Issue on Stainless Steel 316L Light

[Michael Lighting]

Hi all

We manufacturer a light which seem to have an issue of rusting at one site. The stainless steel code is 316L, which has never had a problem but at this site we do. We've had to replace 10 lights and will have to do so again as the client is not happy with our equipment. I feel that the issue could be to do with their water purification, they have told me that they use Bromie to bring up the pH levels and to clean the water.

I am not sure if they use 100 % Bromine, but I think there could be other chemicals included in their mixture, I've asked them to send me the Chemical Compound used in the water. Would this have any effect on our product and if so what can I do to prevent the oxidation happening to our lights at this site.

Also the Pole on the left you can see has got the issue as well above and below, but photos can't be seen on this. I think they are using 304 stainless steel, but could be wrong.

I would Appreciate the help to resolve this issue.

 

[jari001]

This post might fair better in the Metals and Metallurgy forum. If you don't get any input, mark the post with the "Report" button and ask for it to be moved.

 

[EdStainless]

Do these spend time partially submerged? Is the rusting at the water line?
Where is this location? Near the sea?

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[bcd]

Is it free iron embedded into the surface during the fabrication process? For example, carbon steel rollers or wire brushes? If so, passivization of the parts after fabrication will fix this.

 

[EdStainless]

I suspect that it is more likely debris or dried salts on the surface leading to this corrosion.
If it was a passivation issue then they would see it on any application in a humid environment.

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[IRstuff]

Salt and acid atmosphere are deleterious to steels in general. I live off the ocean, and unless the steel was protected or plated with nickel, it gets rusty PDQ. Over the course of decades, even the plated stuff can start to rust, presumably through pinholes in the plating.

It seems to me that you might want to clear coat your fixtures, at least, as a stopgap.

TTFN (ta ta for now)
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[EdStainless]

The worst place for SS is near the coast but under a roof. It gets coated with salt fog every night and there isn't rain washing it off. It takes a very high grade of SS to stand up to this service.
Question should include how salty is this water? What is the pH? And what what is the TDS?
That will tell us if 316 even has a chance.

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[Michael Lighting]

Hi All

I just want to say thanks for helping with this.

Location is Dubai Business Bay Area Opera House, the site itself is about 7.5 Kilometers away from the Cost line.

What I understand about the Site water system is that they clean it. No water content has been checked yet. There is Cover in the Area but does no cover our equipment, but further down where the water travels back to the pumps there is a cover, and if rain was to happen the water from the cover would fall into it.

The Lights do not get submerged completely. Typically the casing sits above the waterline, while the stand holding it upright is submerged in water. There have been cases over the last year where it has rained and the area starts to flood. The nut has got no indication of rust yet.

The Casing is done by lathing CNC Specifcations on the tool bit are

Model: WNMG080404
- Material: Carbide
- Size: 16.5 x 5mm(Width * Thickness)
- Inner diameter: 4.8mm
- Machining Process: finishing and semi-finishing
- Blade color: Gold


What Does TDS Stand for?

 

[springrise]

TDS = total dissolved solids in water, measured in a lab as mg/liter,
conductivity measurement is related and equally helpful information

 

[IRstuff]

The probably high humidity might allow the salt fog to go farther inland. Probably MIL-STD-810 salt fog testing every day of the year.

You might want to ask some local contractors how they deal with steel fixtures

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[EdStainless]

Do you acid clean these after they are manufactured?
Traditionally this is done in room temp nitric acid (25%) for about 15-30 min. An alternate is a product called CitriSurf, it is citric acid based. Less aggressive, safer to handle, but must be heated to work. When I tested it it think that we used 145F for 1 hr. This passivation process cleans the surface. It removes any free iron from handling and such it also will remove very small fragments of SS that would be prone to corrosion.

Being submerged is easy service, the wet/dry cycling is hard. When it drys out the remaining salt residue is concentrated. So these are getting coated in 26% salt every cycle.
A better surface finish would help, and a coating might help for a while, but in reality 316 will not cut it. You really need a very robust coating like this

https://www.uscoatings.com/blog/vsc...-coating-with-superior-long-term-performance/

Or to move to a higher grade of SS. Ever thought of 2205?

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[Michael Lighting]

Hey all

I had to do some digging and gets some answer from various people.

Springrise

The client was able to give us some data on the water content. Hope this helps

IRstuff The Area does produce a lot of fog during the winter season out here. I am not sure where to start to find out information about the fog salt content. With Regards to the local contractors, I have been in contact with them. They're having an issue with the drainage covers with rust. We can't seem to work out why this location and not others.

Ed Stainless

We don't do any acid treatment afterwords. We have lights in the field which are always underwater with no rusting to date, but this site alone is having that issue. We are unsure if it is because of the dry and wet environment that could cause this. We will have to test these lights in the same conditions to see what is going on.

 

[EdStainless]

That is not good water, and a $hitload of Br which is not good for 316SS.
Cyclic wet/dry makes it much worse.
In order to work here you will either need a better grade of SS or some special surface finish.
Perhaps in this case electropolish would help, but I sort of doubt that it would be enough.

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[IRstuff]

As mentioned above, cycling, particularly wet/dry is particularly bad. There's also a strong reason why MIL-STD-810 uses salt fog has the stressing environment for qualification of products that get exposed to a marine environment. A few hours of salt fog can be like years in salt water.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[chicopee]

Your situation about rust on stainless steel components is reminiscent of the problem that happened to stainless flat head screws for a plastic plate located inside of my above ground pool for the skimmer attachment. With my very first pool, none of the stainless steel flat head screws rusted and that pool lasted about 20 years. When I replaced it with an identical one, all of the flat head screws were showing rust stains within a few years eventho. the chemical treatment over the years had not changed.

 

[georgeverghese]

Hypobromite may be a more potent biocide compared to hypochlorite - with corresponding corrosion concerns. From memory, we used superduplex SS (25-27Cr) in similar applications. Else reduce hypo injection if possible.

 

[Michael Lighting]

Hi All

I just want to thank you all for the help with all of this, massively appreciate it.


Spoken to the client and they have been rather reasonable about the situation. I had to present them some finds on the internet to present them the case as to why it is happening. Thank you all for confirming to what it could have been.

The next step is to help them find an alternative way to keep the water bacteria-free and help prevent the rusting issue happens faster?

Any recommendations?

 

[TiCl4]

As an alternative to halogen salts, what about exploring BIT, CMIT, or MIT? I have no idea about the regulations around those biocides in your application, but they are not aggressive towards 304 or 316 SS.