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Harford County Signs and Banners Blog

When It Comes to Outdoor Signs, Is Stainless Steel Just Stainless Steel?

Monday, October 31, 2011

Often you hear people refer to something being made out of stainless steel and it did not hold up or continue to look bright and shiny like they thought it should. There can be a number of reasons for this but 99% of the time it comes down to 2 things:

  1. Material Selection
  2. Contamination

(Sign) Material Selection:

There are numerous alloys that are considered stainless steels. The three basic classes are austenitic, ferritic and martensitic. The most common (most of what people see) are the austenitic stainless steels. These have for the main alloy components chromium and nickel. These are the nice bright stainless items you see like food tanks, tankers and process tanks for dairy and other food products. There are many grades but some of the characteristics we are familiar with are the shiny surface, non-magnetic and resistance to most daily corrosive environments. The austenitic steels have a minimum of 10.5% chromium which results in chromium oxides forming on the surface that creates the protective surface on the metal.

Contamination (of sign metals):

In an earlier post about appropriate sign materials we spoke about sign fasteners and how they had an impact on your sign. The same can be said about stainless steel. When people have said they saw a nice shiny stainless item that had rust on it, it is most often caused by the surface being contaminated by iron. A standard steel fastener or fitting is placed in against or has rubbed against the stainless surface and contaminated the oxide surface that protects the stainless with iron. This can be remedied by mechanically scrubbing the surface with stainless wire wheels or wool, and then passivating the surface with a solution of 10% nitric acid.

So now the real question: How does this relate to signs?

When you deal with dimensional letters they can go just about anywhere. If you are dealing with a location that is close to ocean, or has a large amount of industrial pollution, these factor can impact your choices of materials.

Let's consider being around the ocean. The salt air that we all enjoy contains large quantities of chlorides. These can have negative effects on materials like aluminum, especially if there are residual stresses in the sign from forming. So we would suggest stainless steel letters instead. But in most cases dimensional letters are formed into shape and then welded. This also can cause issues down the road in a salt rich environment. This is where material choices are nice within the stainless family. We have available letters and signs that are fabricated from 316 stainless as well as 304 stainless. In most cases 304 is a great choice but when it comes to a high chlorides (salt) environment, the additional alloying elements in 316 will keep your sign looking better longer than standard 304 stainless. There is a premium you pay for the addition of molybdenum (moly) in 316 as well as the availability, because 304 is much more common. But in the long run, it is "Pay me now or Pay me later" when it comes to these choices.
At Blue Water we know that the choice of sign materials can add lasting value to a sign installation. Making the right material choices early in your decision process can create a favorable impression with customers longer into the future.

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