Cor-ten type steel for atmospheric corrosion resistance of a fan housing

[Tmoose]

Preliminary information is the fan is located near the cooling towers, so it has experienced 30 years of corrosion. Recently efforts have been made to sand blast the fan housing for painting, but the customer is finding the metal is extensively perforated. It is a Forced Draft fan, so handles relatively cool, clean ambient air. I am pursuing details about how the housings are REALLY failing. Outside in, inside out, possible erosion , etc.

I'm thinking 30 years of service is pretty good, and cleaning and painting every 5 years or so might have made a big difference.

It has been suggested that Cor-ten housings should be used. My concern about supplying a fan housing made of Cor-ten is, if the cooling towers are making the humidity high and constant, the Cor-ten may not fully develop the protective layer, so corrode and yet not accept paint very well. Fan literature generally only talks about using Corten for its good mechanical properties at high temperature.

Does Cor-ten really sound like a good option for improved corrosion resistance in this (poorly defined) application ?

thanks,

Dan T

 

[kingnero]

As you say, I doubt (but I am not sure) that the oxide layer will be strong enough to handle any erosion. This means the material will form oxides continuously, rendering it like any "normal" carbon steel.
Are stainless steels not an option?

I am not sure I understand you correctly, but are you thinking of using Cor-ten steel and painting it???

 

[MJCronin]

Stainless is an expensive idea ....

Have you called the people who sell CORTEN steel and asked them ?

The steel and metals industry have been using CORTEN for fan housings for decades ...

This might help ....

http://2.imimg.com/data2/NC/GW/MY-1913761/corten-a-steel-weather-resistant-steel.pdf

MJCronin
Sr. Process Engineer

 

[EdStainless]

Or build a new one in plain steel and coat it properly

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

Coating technology is constantly evolving, this one is the best that I have seen.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Stick.]

If you end up going the Cor-Ten route, make sure your customer knows what to expect as far as the oxide layer and the appearance. My company has had issues with customers complaining about their equipment "rusting" in the first few months when we used Cor-Ten, thinking something had gone wrong. It would have caused a lot fewer headaches and emails if we had explained how the oxide layer works ahead of time.

 

[btrueblood]

Read the wiki article too, about some of the disadvantages of weathering steel. The USS building in Chicago had a lot of staining due to runoff of the corrosion products, had to spend some money to clean the sidewalks after people objected.

 

[MintJulep]

Thin gauge cor-ten and similar steels really don't provide much for corrosion resistance.

Basic regular steel galvanized is probably a better performer.

 

[berkshire]

I thought the whole purpose of Cor - Ten steel was that the higher copper content bound the iron oxide layer, so that the rust did not, flake off, and thereby protected the base steel with the oxide layer. Painting Cor-ten tends to defeat the whole process, because if the paint layer is chipped, the steel tends to rust heavily at that exposed point.
B.E.

You are judged not by what you know, but by what you can do.

 

[GGedge]

Dan T

Weathering steels retard corrosion rates rather than being corrosion resistant like stainless and other alloys. The build up of corrosion product slows transport of oxygen and water to the steel surface and therefore limits corrosion rate. Performance is best when the steel is blast cleaned and exposed in conditions of natural wetting a drying by rain, sun and wind. It performs less well in polluted environments or in chloride environments. Because corrosion continues, all be it at a slow rate, common practice is to provide and a corrosion allowance to counter that. Typically this is in the range 0.5 to 2mm (see FHWA guidance, UK Highways England Standard BD7 and German DASt-007) typically those standard cover long life structures like bridges but the principle also applies more widely.

I imagine a fan casing is relatively thin (at least compared to a bridge beam) and might it be more susceptible to flexing or movement? If so the patina may not tolerate the movement and crack exposing the substrate to the environment and thus the rate could remain high.

While one can paint weathering steels it always strikes me as a bit of an odd thing to do, one is paying a premium for the steel and is not using what one is paying for. It is rarely done but some standards (UK HE for example) do permit future painting if the steel performs poorly. But I would imagine that surface preparation on a fan casing would be a challenge and it might be better to use a high quality paint spec in the first place on normal steel.

Cheers

G G

 

[Tmoose]

thank you, everyone.

Dan T