Steel Corrosion Metric? 4

[Logan82]

Hi!

Is there a reliable metric to measure the speed of corrosion of steel?

Does anyone have a good reference on the subject?

I am wondering about the corrosion of AISI 4340.

 

[GGedge]

The rate of corrosion is dependent on the service environment, macro and possibly micro, so definition of that is the first step.

Cheers

GG

 

[Logan82]

Exactly. But I think it could be great idea to have a lab perform a series of corrosion tests in a controlled environment. Uou could obtain a table with nominal values. It could give us an idea of the corrosion resistance of steel. I would be surprised if something like this didn't exist yet.

 

[jayrod12]

The reason they don't is the high variability of exposure conditions. I've seen steel rot out in a house, and yet keep integrity in more caustic environments. Due to the number of variables, and each of their different effects on corrosion rate, it would be extremely hard to provide any sort of guidance that would be useful. Any guidance they give would be littered with exceptions/limitations to the validity of the results.

 

[GGedge]

They do, sort of exist, in things like salt spray and accelerated weathering tests. OK for comparing A with B in a standard test or showing the product made today performs the same as that produced a year ago. Predicting what those tests mean on real structures in real service environments isn't really credible.

Cheers
GG

 

[EdStainless]

It doesn't work except in highly corrosive environments. In 'milder' environments (polluted industrial air for example) very minor differences in humidity, rainfall, wind and sun exposure, and nearby structures could have a factor of 100x impact on observed corrosion rate. And we haven't even started to talk about microbial factors.
If steel will only last a few years then there are likely good numbers to use. If it will last 20-100 years that is what you have to work with.
This is why there is so much work done on coatings. That is how you get reliable long life out of plain steels.

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[Settingsun]

As per the earlier responses, it depends. Here are some guidelines from Australian Standard AS 2312. It references ISO 9223 which would probably be more acceptable internationally than an Australian Standard if you want to look into it.

Not sure whether your high-strength steel is more susceptible than more typical steel grades. Is it for bolts?

 

[Logan82]

Thank you all for your answers.

Steveh49, the table is interesting.

GGedge, comparing the corrosivity of A vs B steel grade in controlled environment could already be interesting.

The AISI 4340 is for a structural pin in a hinge.

 

[GGedge]

That testing might be interesting academically but is of no practical use.

Note in relation to the AS table above, the current version of ISO 9223 on which it is based, does not include the T class that is unique to Australia. Also the C5 condition is no longer split but is just C5. Remember the rates in the table are for the first year of exposure, look in ISO 9224 for how to deal with long-term rates. The data is for samples fully exposed to the service environment and takes no account of localized effects. For a pin corrosion risks are more than likely controlled by local effects resulting from the pin details than the general case.

Cheers

GG

 

[EdStainless]

The worst natural corrosion environment that I have worked with was coastal under an overhang (no rinsing from rain). The salt accumulation, high humidity, and heat combined to eat up almost anything metallic.
The used to be a US doc similar to that (DoD or Navy) listing general classes.

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