Super Duplex SS Time required for natural passivation 3

[Hercules28]

Dear all,

Does anybody know or has any experience with Super Duplex SS?
Assume that I scrape it or machine it. How long should I wait for the chrome layer to buildup? Is it hours , days or months?

I don't want to put the pipe in service and see any rust!
And passivation is not an option.

Thanks,

Herc

 

[enmax]

I would check first that you actually do have any iron contamination. A ferroxyl test (ASTM A380) on some finished parts would show whether you have a problem.

http://uk.linkedin.com/pub/terry-roberts/28/a9a/a10

 

[Jandyr13]

Please,

I need some help to eliminate porosity in valves of duplex steel (cd3mn).

What's the better deoxidation for this kind of DSS.

A lot of thanks.

 

[EdStainless]

Attention, H-28 McG, and others.
Time to passivation.
After extended discussions and a couple of well researched papers this year at NACE I have changed my mind on the issue of time to passivation.
When corrosion testing samples of SS there is a detectable change improvement in corrosion resistance over 72 hours after sample prep. There is no discernible difference between 72hrs and 240hrs, but there is a measurable difference between 0, 24, and 48 hours.
This effect held regardless of the sample prep methods, grinding, blasting, pickling, passivation, and various combinations all showed the effect.
In the real world this not much of a deal since it is rare for parts to go into service in less than 48 hours from finishing.
However in the lab it is a concern. Either test everything ASAP and get more conservative results, or let all samples sit 72hr min and get slightly better results.
I know, this should prob go into another thread. When I get a copy of the paper to read again I will start a thread on this subject.
Ed

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[Hercules28]

Ed, valuable info. do we have this paper from NACE?

I did some research myself in scientific research and I only found instantaneous formation of the layer in a fraction of a second.

 

[cloa]

People do realise that those passive films vary in thickness and nature depending on the solution that the metal is in however a thicker film in one solution in no benefit in another solution. It won't be stable.

 

[Hercules28]

Cloa you are right about your comment. Thicker film doesn't always mean better film. I found a scientific paper from 1985 I think from Cambridge that was debating on whether the Cr is building an oxide or the Fe is getting dissolve in the acid. Very interesting.

Ed,

I went through 3 years of NACE publications but I didn't find anything specific on the subject of this thread. Do you have any leads ? I got like 20 articles to skim though!

 

[EdStainless]

The paper is C2012-0001644 by T. Ladwein and M. Sorg
It is from this year.
Ed

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