Speeding up the oxidation of COR-TEN 1

[jka8s]

Dear all,

Can anyone provide any info or resources on sucessful methods to speed up the natural ~ 3yr. oxidation time for COR-TEN steel to a matter of days? I have heard that although, generally, pretreating is not recommended it can be done. Has anyone had success doing this without doing more long term harm than good from an aesthetic or performance standpoint? If so, what patinating agent and application method would be appropriate. Any assitance would be greatly appreciated.

 

[HgTX]

Dr. Desmond Cook at Old Dominion University has been known to work on weathering steel and might have something useful to say.

http://www.physics.odu.edu/cmmp/CMMP_GroupBrochure.pdf

A couple of years ago he was working on something to allow weathering steel to form its patina despite being immersed in water, or something like that.

Why do you need this?

Hg

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[dik]

Just a caution... although Cor-ten forms a tight oxide surface, it can still stain surrounding concrete.

Dik

 

[unclesyd]

What is the size of the component that you want to force an
oxide coating on?

 

[jka8s]

The component is sizable. Along the lines of an exhaust stack.

 

[unclesyd]

Size is a problem for what I was considering.
I done a lot of work on the steam/air oxidation to force an oxide coating on carbon steels when we were evaluating anodes. I've been scanning my notes to see if Corten was looked at.

 

[HgTX]

Just to be nitpicky, "Cor-Ten" as a brand is almost gone. US Steel has gotten out of the plate business, and I don't see any rolled shapes on their website either. Cor-Ten seems to exist only in sheet material now.

But other mills make weathering steel (ASTM A 588 et al).

Hg

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[rorschach]

HgTX, Cor-Ten is also known as SAEJ410 Grade 950D and ASTM A242 and ASTM A606 type 4.

If the part is immersible in a tank, perhaps a reverse galvanic cell could be used to acellerate the formation of a patina.

 

[unclesyd]

In checking our group did do some testing of forcing the oxidation unfortunately I was involved in this part.

Aside from the process mentioned above we used several methods and all involved Chlorides.
One was to expose the component to HCl vapors at ambient temperature.
Use a saturated solution of NaCl and spray on the part let sit for several days and rinse off. Repeat.
Use an acidified solution of NaCl about 1% HCl by volume to the saturated solution.
We also used an acidified solution using Acetic Acid and
NaCl.

 

[yates]

Funny you should want to accelerate the corrosion of COR-TEN ! The patina formed on COR-TEN in atmosheric conditions was often mentioned as an advantage in architectural use on face of buildings etc. I have considerable experience in design and follow-up of COR-TEN chimneys stacks for Gas Turbines. Patina is lovely but falls to dust with vibration, and results in even lower useful life span than lesser steels.

 

[swall]

Unclesyd--I am surprised to learn that chlorides were used to enhance the oxide layer. About 25 years ago, Michigan DOT was big on Corten for highway overpass girders. Then they found that they were rapidly deteriorating due to road salts used in winter.

 

[unclesyd]

We were attempting to force the oxidation of CS when the end result being a layer of Magnetite for use as an anode in a electrolytic cell. The basis for our approach was CS exposed to Salt Water or HCl vapor overtime will develop a layer of Magnetite overtopped with loose Fe203. Other work had shown that once the formation of Magnetite had started we could enhance the growth of the magnetite layer by another process precluding the formation of the other oxides.

It turns out that plain CS was the better anode material.

 

[HgTX]

swall--I'd think there would be a difference between a one-time application to induce oxidation and repeated cycles of chloride application over the course of a season or several years. If subsequent exposure to wet and salt disturbs the patina, then you're back where you started, only with less steel than you had before.

Hg

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[pecidar]

I have heard of using a salt water wash to accelerate the natural patina formation on weathering steels. Pre-fabricated bridge manufacturers typically employ this method strictly for aesthetic purposes to provide a uniform appearance on finished material prior to shipment. I am not aware of any detrimental effects to material when doing this.

 

[rorschach]

Heh, Cameron Iron Works' building here in Houston used an HSLA steel in a visible architectural use for just such a patina, now the surrounding conrete looks like hell and they were constantly power washing it to try to stay ahead of the stain, they eventually blasted and painted it to stop the mess. I'm not sure but I think the Architect is hiding somewhere in Mexico right about now....=D

TXDoT did the same thing with a number of HSLA steel fabricated bridge beams around town and failed to paint them, the rust streaks look like crap too. All for want of a few hundred gallons of paint.....

If an architect or civil engineer ever tells you he doesn't need to paint because the patina will protect it from corrosion, just shoot him and get it over with. He may be right, the patina will prevent corrosion but the stain will never look good.

 

[HgTX]

TxDOT did some notorious weathering steel bridges that they didn't detail properly to prevent staining, and they look like utter crap. (What they should do is go back and just paint those columns brown...)

TxDOT has since done quite a few weathering steel bridges that are designed not to drool rainwater down the concrete supports, and they look fine years later. In Houston they did all the detailing and also painted the ends just to be sure, but the color match is awful. In Austin they didn't do any of that and they're fine.

Paint would still be required near expansion joints in areas where road salt is used, to protect the steel from such an aggressive corrosion environment (and in such cases I'd probably advise painting the whole fascia surface to avoid the color match problems), but the key to avoiding the ugly staining is in the detailing--drip bars, weepholes, drains in the columns, etc.

There are a number of guides out there for detailing weathering steel to avoid staining. I don't really know how well any of that would work for a building. (If anyone has any building references I would be quite interested.)

Hg

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[RustDr]

Saw my name listed on first reply.
Yes we have completed testing a new Active Coating for Protective Patina Formation on Weathering steels in 1-2 years exposure. Corrosion decreases X10 in zero-to-very high chlorine environments, and all wetness. No bleeding. Can be colored or natural patina color. Search PatinaForma for details and my contact info.