Blogs | Ethan Shorey

Built to rust

The new $4.3 million Conant Street Railroad Bridge in Pawtucket took 25 years to complete, so it only stands to reason that some city residents would inspect the structure with a critical eye.

After hearing from one of my trusty tipsters that a “little bird” informed him that the metal on the bridge is “totally rusty,” I thought a little explanation might be helpful.

For anyone concerned at the fact that the new bridge has rusted over just a month after it opened, fear no longer. This bridge is not due to be replaced again for another century. It turns out the span is built with the same type of weathering steel that covers the outside of the Barclays Center in Brooklyn. That building “already looks as if it has aged decades," according to a story in the Business Insider.

“The steel develops a layer of rust which protects the metal against moisture, and slows the corrosion process,” it states. “The result is a tawny hue that stains the concrete below orange as the steel drips - not exactly a passerby's dream.”

A Rhode Island Department of Transportation spokesperson told me last year that the weathering steel on the new Conant Street bridge allows it to rust over so as not to require as much maintenance going forward. In other words, it may not be the prettiest bridge ever, and is certainly no Pawtucket River Bridge with its arts-inspired lights, but there will be no need for paint jobs.

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Comments

"Tawny" sounds like a colorful euphemism concocted by the marketing department, while "post-apocalyptic" might be more on the mark. I was horrified the first time that I saw the enormous rusting, looming poles (presumably constructed of the same material) carrying high tension wires bound north at the east-west intersection of routes 6 and 295 in Johnston. (You can see them on google maps if not familiar with the image.) Surely they would not inspire confidence in any "gateway."

One detail about the material which bears watching is the following from http://www.corten.com/frequently-asked-questions.html

...
Climates NOT to use COR-TEN®:
COR-TEN® steel requires alternating wet and dry cycles to form a properly adhered protective layer. Areas that have salt laden air, high rainfall, humidity, or persistent fog are typically not the proper environment for COR-TEN®.
...

A wikipedia article about weathering steel (not well sourced, so it must be taken with a grain of salt) says:

...
COR-TEN was used in 1971 for an order of electric railcars built by the St. Louis Car Company for Illinois Central Railroad. The use of COR-TEN was seen as a cost-cutting move in comparison with the contemporary railcar standard of stainless steel. A subsequent order in 1979 was built to similar specs, including COR-TEN bodies, by Bombardier. The cars were painted, a standard practice for COR-TEN railcars. However, the durability of COR-TEN did not live up to expectations, with rust holes appearing in the railcars. Ironically, painting may have contributed to the problem, as painted weathering steel is no more corrosion-resistant than conventional steel, because the protective patina will not form in time to prevent corrosion over a localized area of attack such as a small paint failure.
...
Source: http://en.wikipedia.org/wiki/Weathering_steel

If it is true that the material does need "alternating wet and dry cycles" in order to form its coating, then it is plausible that painting could indeed exacerbate undesirable rust and deterioration. And in any urban area, walls and metal structures are more often painted (some would say "tagged") by the local youth than by city or state maintenance crews.

And it does make you wonder whether we are trading the incessant cost of painting crews for the cost of paint removal crews.