Weathering Steel vs HDG 4

[ldeem]

I work in mining and am in the process of designing a replacement 90' truss. This is a limestone facility and the truss will be part of material handling system. Corrosion is a significant problem at the site. In the past we have used a lot of HDG but that can be hard to do on larger trusses, not to mention costly.

I was thinking of looking at weathering steel as an option. I have seen it used on some heat exchanger hoppers and it has held up relatively well.

I am looking into the price difference now but my question is if anyone has used weathering steel in a similar situation and has it stood up over time? This location gets a lot of material buildup (limestone fines) which tends to build up and would trap moisture. I understand weathering steel doesn't perform well in that situation.

 

[dik]

If subject to abrasion, weathering steel can 'corrode' faster. It can also 'stain' the surroundings with it's 'rust'.

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

-Dik

 

[wrantler]

If it will have material on it that will be moist then not good. You should let weathering steel breath for its patina to do its work.

Maybe look into coating systems. But HDG may be the best bet.

 

[GC_Hopi]

It will come down to cost like the OP mentioned. As far as cost efficient I would probably put my bet on HDG. The other item that needs proper care is the detailing. Better detailing will extend the life of the steel.

 

[JLNJ]

Depending on how long the previous version lasted, stainless might be an option.

 

[dik]

GCH... you should see some of the electrical cable trays in some mines...

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

-Dik

 

[bridgebuster]

Attached is guidance on the use of weathering steel.

 

[JoelTXCive]

The Texas Department of Transportation (TxDOT) has used weathering steel extensively on bridges.

From a structural and durability point of view, I think they have been very happy. From a cosmetic point of view, they have had a lot of problems with staining of surrounding structures as the weathering steel rusts.

The aesthetics might not matter for your use though.

 

[dvd]

Curious whether the weathering steels have good low-temperature properties - what is the minimum service temperature for this truss?

 

[dik]

They are used in our area... subject to -30C and colder. As far as durability, as long as the coating remains, they are good. They were used for the hydraulic ram guides for the local floodway, subjected to water flow with 'stuff' and they didn't do very well... The particulate accelerated the corrosion. Some of the guide beam web and flanges, nearly disappeared (fish (tiny fish) could swim through the webs).

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

-Dik

 

[JedClampett]

If the truss is to be fabricated in one piece, you might run into your local galvanizers' kettle size limit. A 90' truss can be dipped twice into a 45 ft. kettle, but the depth might make things complicated. Check out galvanizeit.org for what your closest galvanizers can do.

 

[ldeem]

Thank you to everyone for your replies and sharing your experience.

Client isn't sounding too keen on the idea right now. Mainly because it is nearly impossible to keep structures cleaned off in the field.

I am still going to rough out cost differences and will update the thread.

 

[dauwerda]

I work in the utility industry and use both weathering steel and HDG steel everyday. From a price perspective for the plate steel we are using to fabricate multisided columns, black steel (A572 Gr. 65) and weathering steel (A871 Gr. 65) (also A572 Gr. 50 vs A588 Gr. 50) are essentially the same price. This makes weathering steel a bit cheaper as there is no galvanizing cost. I don't know if the material cost is the same for rolled shapes like it is for plates, but I would guess they are similar. That said, this really sounds like a less than ideal application for weathering steel. As you noted, material buildup with moisture and weathering steel do not mix.

 

[bugbus]

dauwerda, in terms of rolled sections, I'm not aware of these being available in weathering steel (have never seen them personally).

So there is some additional fabrication cost for weathering steel bridges because the smaller bracing elements that would normally be made from rolled angles or channels etc. would have to be fabricated from plates.

 

[dik]

The floodway ram guides were 24" deep S sections, and I've seen lots of W and C sections in this area... also HSS sections.

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

-Dik

 

[hokie66]

The bridge which collapsed recently in Pittsburg was weathering steel. Corrosion due to prolonged water in non-draining details seems to have been the cause.

 

[BridgeSmith]

We've specified weathering steel wide flange sections for bridge girders, and the contractors didn't seem to have any problems sourcing them.

That said, this doesn't sound like a place where you should use weathering steel.

 

[bugbus]

Interesting, possibly a regional thing.

I know that a lot of weathering steel is made in North America, maybe also in Asia. I suppose it is much more cost-effective to ship flat plates than it is rolled sections, which might explain why we never see the latter in Australia.

 

[BridgeSmith]

Yeah, in the US, most rolled shapes, and HSS are available in weathering steel. We like it for bridges, not only because we don't have to maintain the paint, but it also carries a higher ultimate tensile strength (Fu = 70 ksi vs. 65 ksi for A709, grade 50).

 

[kingnero]

Curious whether the weathering steels have good low-temperature properties - what is the minimum service temperature for this truss?

In Europe, CorTen has normative values ranging from S355 J0 upto S355 J5/K2, which is quite impressive to be honest.