letter 51622

Rusting Of Stainless Steel Railings

March 18, 2009

Dear Mr. Newton,

We are fabrication company, who is taking care of stainless steel fabrication and installation. one of our projects, the Aquarium Museum, we have installed Stainless Steel railing (just at the top of the fish tank) of 316 Grade as required by the client to use the stainless steel marine grade. Now the railings get rusted, and the client is telling us that this happened because we didn't use the marine grade 316L.Our understanding is the the marine grade is the 316 and not 316L, is that right? then the client is proposing another detail of the railings where he is going to use 316L, and we think that since United Arab Emirates (Dubai) is a severe corrosion environment, and since we are going to put the new railings at the top of the fish tank, then we think that the railings will rust also.

Please advice.

Thanks

Mohammad Shahrour
Metal Fabrications - Dubai, Dubai, United Arab Emirates

These days it seems like stainless railings, etc., won't hold out forever in any chloride environment (oceanic coastal areas, swimming pools), but with good passivation and periodic repassivation the onset of corrosion can be forestalled as long as possible. With citric acid based formulations, corrosion clean-up and repassivation can be done on site. Let us know if we can help.

Ray Kremer Stellar Solutions, Inc. McHenry, Illinois

Dear Mohammad,

There is no significant difference in corrosion resistance between AISI 316 and AISI 316L. Only in the welding zone, AISI 316L will perform slightly better.
It is normal that SS 316 or 316L is rusting in marine applications. The only known solution until now, to prevent AISI316 from rusting in marine (and most outdoor applications) is by electropolishing. In Belgium, this treatment is successfully used for all outdoor stainless steel applications. Most outdoor SS which is not electropolished starts rusting within a year - unless you clean often.
Kind regards,

Marc Quaghebeur
- Brugge, Belgium, Europe

For resistance to the chloride in marine environments, which 316 and similar old grades can't handle, go to a duplex such as 2205.

Bill Reynolds    consultant metallurgist Ballarat, Victoria, Australia

I couldn't agree more with you Marc,

Not only in Belgium, but also in the Netherlands, stainless steel which is used for outdoor (marine) applications is more and more electropolished. Besides that, over the last years we did some testing with all kinds of finishing and treatments of stainless steel in the United Arabic Emirates and the outcome of all those test pointed out that electropolishing is the best treatment for stainless steel used in outdoor applications.

Klaas de Boer
- Heerenveen, the Netherlands

As Klaas and Marc stated electropolishing is by far the best way to increase corrosion resistance of 316 or 304 used in marine environments. It should be used as the last step in the manufacturing process.
Concerning hand railings, its a unique challenge as a lot of railings are welded on-site. We usually tell our clients to electropolish as much of the railing in-house and then electropolish the welds on-site. Another inherent problem with hand rails are...they are exactly that...hand rails and will be touched, rubbed on scratched etc. This can create voids in the passive layer and lead to way-in-the-future corrosion. By the time the corrosion is visible usually the handrail is well-used and can be re-electropolished on-site. Do not use steel wool to clean stainless under any circumstances!

Cliff Kusch
electropolishing shop - North Vancouver, BC, Canada