Where the
world gathers for metal finishing
Q&As since 1989


-----

Stainless is rusting in Maui condo complex

I am president of a 240 unit condo complex on Maui in Hawaii. Much of the hallway lighting consists of 6 inch white glass globes that at night send light in all directions including into the bedrooms. After much experimentation, we found some stainless steel salad bowls at Walmart, cut holes in the bottom of them, and turned them upside-down to act as shades. Their polished inside did a great job deflecting light downward on the walkways while keeping it out of the bedrooms, but their brushed exterior is rusting after a year. Some pitting of the inside that no doubt occurred during the hole cutting is also rusting. We thought stainless wouldn't rust. Someone told me the bowls exteriors were likely brushed with steel and it's that steel residue that's rusting, and that the bowls need to be "pickled" or "passivated" in a tank that a plater would have. This explanation doesn't account for the rust pits on the inside however. If anyone has anything to add to this diagnosis and proposed solution I'd appreciate it. Short of being able to fix this problem, I am thinking of getting some chromed plastic shades made but have no idea where to look. If anyone can steer me in the right direction there I'd also appreciate it. Incidentally, we need about 200 of the shades and they are 6 1/2 inches tall with a base that's 5 1/4 inches that has a 3 1/2 inch holes cut in it. Inside diameter is 11 inches.

Warren Woodward
President, condo association - Kihei, Hawaii, USA
2004

---

Aluminum reflectors are higher in reflectivity than either stainless or chrome, while not being subject to rust. I would suggest doing a search with terms like "aluminum luminaire reflector".

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

The bowl is probably a 400 series stainless. It lacks the nickel to retard corrosion. Try touching a magnet to it. If it sticks well, similar to steel, it's a 400 series. The advantages are a lower price, easier workability and, for some alloys, the ability to be heat treated. You need a higher grade bowl. A 300 series stainless may have some slight magnetic attraction but very slight. Some of the manufacturers may produce the bowls from any stainless that is available on the secondary market so you may find the 300 if you keep looking. You may be able to find something that would be comparable from a distributor of equipment for livestock. Most stainless used is a 300 series because of the corrosiveness of animal urine. One problem you will run into is that the 300 series work hardens rapidly. you may want to find a shop that can punch the holes rather than trying to drill them. It will dull the bits rapidly.

Patrick Records
Non ferrous service center - Cleveland, Ohio
2004

I agree with the aluminum idea but the other suggestion is incomplete. The salad bowls may very well be 304 stainless steel. However, they need to be at least 316SS to have a reasonable resistance to chloride attack. It is the molybdenum content that increases chloride resistance.

Mark Cook
- Springfield, Missouri
2004

Thanks so much for all responses; your help is greatly appreciated. I like the aluminum idea but am concerned it will oxidize and get chalky (we are across the street from the ocean--good for views, bad for metals). I have also had a hard time locating manufacturers that will reply. I tried a magnet on the stainless and it doesn't react. Nevertheless, I think the problem lies in the alloy. I would think that the right alloy really shouldn't rust. I intend to research getting some made in the correct alloy and also chromed plastic. I have chromed plastic speedo & tach housings on my parked-outside bike and it's holding up very well. If anyone has suggestions, I'd appreciate them.

Warren Woodward
condo association - Kihei, Hawaii, USA
2004

Don't be confused about aluminum, it will rust over time especially in the climate your located in. I have found this to happen on tractor trailers. You do have a problem with the grade of stainless, and you would have a problem drilling through a higher grade. I would consider either going to a higher grade or going to a polished aluminum only if your not using a high wattage bulb which will tarnish in the climate your in.

Jonathan Smith
polishing, metal fabrication - Eastman, Georgia
2004

Yes 400 series stainless will rust but 400 series is not used in making food containers. I am taking a guess but I bet that they are plated and not stainless. If you are getting a lot of the rust starting from the drilled hole I would tend to believe that is the case. 300 series stainless would last longer than alum or anything else I could think of. If you want to get replacements I would bring a magnet with you before buying.

Martin Borho
- Ticonderoga, New York
2004

---

2004

I am wondering about the possibility of having your existing bowls plated with molybdenum, nickel, or any other compatible plating material that is more resistant to the salt water air. Both of those alloys are very beautiful and salt-water resistant. Electroplating is a finer finish form of plating, but can be difficult on certain shapes, etc. A plater will know if you can have your bowls successfully pickled and plated. I am not familiar with the "electro-platability" of stainless because it is typically non-magnetic and thus may not be suitable for this process. It's worth looking into as an effective option that will save the investment you've already made in the existing bowls. I don't think passivation will be effective because your bowls are obviously a lower-grade alloy. A 316 or better (marine grade) alloy would be more suitable, but also more difficult to work with because the high nickel content,etc. makes them harder.

If you really want nice fixtures you could perhaps have a low-carbon version of marine grade stainless made into bowls through a process called "spinning". Be sure if you choose this option to use a contractor very familiar with salt water problems, because the type of tooling/environment during the spinning process will definitely effect the corrosion-resistant effectiveness. Also, check what other materials are touching the stainless steel bowls for conductivity which creates galvanic action and will make them rust more rapidly...especially a stainless steel alloy with a highly ferrous content...steel, copper and other alloys that are touching your bowls as part of the light fixture(look up a galvanic chart on the internet to understand this process/how it effects stainless steel) could contribute to your problem.

I am making educated guesses from my experience as a metal worker dealing with similar challenges in a salt water climate. Check with the experts to see if these suggestions are viable! Best of luck!

Sarah Parker
- Seattle, Washington, USA

---

2005

In case someone else stumbles upon this thread as I did, I thought I'd post my two-cents.

All of the other responses suggested ideas that seemed like they'd be quite costly. On a more frugal note, how about taking the bowls/lamp shades down, cleaning them up with naval jelly [on eBay or Amazon] (or whatever rust-remover you prefer), then applying 3-4 coats of a protective, glossy clear-coat meant for metal? (I know Rustoleum makes this available in a spray paint-type can.)

I'd be interested in hearing some expert feedback on this idea.

K.K. Lambiotte
- Ventura, California, USA

A clear coat product may combust in proximity to the heat of a light bulb.

S. Martin
- Thomasville, North Carolina, USA
May 5, 2011