Corrosion from Road Salts 6

[dik]

Is SS316 better than SS304 for corrosion when subject to road salts? Is there a better material that is reasonably inexpensive?

Thank, Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Neither are acceptable. 316 is ok for immersion in salt water but road applications involve drying which super-concentrates the salts. Under these conditions there is no reliable 300 series stainless steel. If you can keep it dry or wash it frequently they'll work. 316 is generally more corrosion resistant due to the Mo addition.

Do provide some additional conditions if you want a recommendation. Copper, aluminum, and titanium alloys are generally resistant to the problems associated with chlorides. Aluminum alloys are subject to the same crevice corrosion issues as stainless steel and are required to be kept clean. All of these alloys are subject to erosion damage. Nickel alloys are harder and more resistant. Duplex stainless steel work around many of the problems but I don't have experience to make a recommendation with regards to duplex alloys.

 

[dik]

Thanks, tug... The hanger assembly is located underneath the bridge in a bit of a sheltered location. I don't expect it to be frequently wetted, but there could be a lot road 'mist'. The bridge is located in northern Canada, and I suspect traffic will be somewhat subdued.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

You have described the worst case scenario. Infrequent wetting implies drying which may result in chloride induced stress corrosion cracking. I have seen cold drawn bar fail without any load applied due to residual stresses.

The sheltered location means there will be no washing from rain or other sources. Again, this is a problem. Stainless steels require cleaning in order to remain stainless. Any deposits on the surface will initiate crevice corrosion.

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hacksaw]

We used monel in the in process applications. Even minor chlorides tear up 304,316 SS.

Tug has nailed the concerns and the solutions, stress corrosion cracking of stainless can be astonishingly severe.

 

[dik]

Thanks... I'm looking into 2205... I knew that regular stainless has a problem with chlorides, but didn't know it was that severe. I'll also look into fiberglass and HDG as an alternative.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

The duplex alloys eliminate SCC but are still susceptible to crevice corrosion. It appears to be much more resistant to crevice corrosion than 300 series alloys but all studies I can find refer to a submerged sample. Being in open air is a much more challenging condition. 2205 should be acceptable provided you can keep everything clean.

 

[dik]

Thanks, tug... I'm leaning to HDG and fiberglass or 2205 as a possibility. I think the HDG is quite a good solution; I'm familiar with HDG and road salt effects. The conduit hangers will likely be in place for years. They are out of the way, and will not likely be 'inspected' once they are installed.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

Agreed this is the worst situation possible
2205 is a decent option.
It does have useful SCC resistance, especially since we are not talking about elevated temperatures.
But before I went that way I would check to see if the location is using MgCl2 (often in a slurry mix).
If they are then don't use any metals.
HDG would work, but then you always worry about the connections.
Are there fiberglass options that will tolerate the cold weather?
You might look into the rules/material for hanging things overhead in a swimming pool building.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks Ed... looking at using HDG Cooper B Line, something similar to below. I have to get some material thicknesses. Load is only 25lb per hanger or thereabouts. Contained cable is fiber optic stuff. I'll also include a requirement that this be 'inspected' every 5 years, or so. This is the current rendition.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Fiberglass pipe and threaded rods and nuts are commercially available.

 

[dik]

thanks, tug... I'm still waiting to find out what type of salt they use... if regular chloride, I'll likely use HDG if more economical. If they don't know, I'll likely go with fiberglass. Loads are really light, but has to be hung down from the U/S of the deck by 6" or so to clear some other conduits. For pulling the fiberoptic, they want to keep the run as horizontal as possible.

First comment back from the client is that the conduit is on the U/S of the deck and not exposed to deicing salt... I suspect there is a light salt mist that accumulates...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

You are on the right track Dik.
Salt mist from the road is real, as so are deck leaks.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks, Ed...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Stick.]

dik: The report below confirms that salt mists would almost certainly be a concern in your case (just in case your client needs any convincing on that matter).

https://www.imoa.info/download_files/stainless-steel/DeicingSalt.pdf

 

[dik]

Thanks Stick... just skimmed the paper, it appears to be very good... to keep for future reference.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Stick... Rather than just skim the paper you attached, I just read it in detail; this is an excellent publication. Thanks, again.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Stick.]

No problem. I originally heard the paper mentioned in this AISC webinar on structural stainless steel, which unfortunately isn't offered as a recording. If they ever offer it again, it seemed like a good primer on AISC 370, 313 and Design Guide 27.

 

[EdStainless]

I'll not that people often point to testing with various Cl salts on 304L coupons and say that there is a threshold temp for SCC.
However in the real world we don't just have salts we also have various organic Cl compounds (usually chloramines).
These will drive SCC in 300SS at room temperature, hence the issues with swimming pool enclosures.

Had a customer once that processed salt (NaCl, crushed, sized, and packaged) in an enormous building.
For whatever reason the building had a fire suppression system.
They needed to replace the system and didn't want to just use painted steel, and for whatever reason didn't go with FBE steel.
They went with 316L.
It was a dry system so it was under 40psi of air pressure at all times.
It took three years for leaks to form large enough to allow the air pressure to drop.
When 80psi fire water filled the piping they cracked open hundreds of feet of pipe.
Not pretty.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed