Corrosion on I-beams

[Sergey_]

Hi,

We are working on a project with extensive corrosion on I-beams which support a residential garage. The ends where they go to concrete, are completely gone and you can put a finger through some of the I-beams.

Wondering what could be the reason for such extensive corrosion? The whole length has some degree of coating failure there, but just the end sections (approx 1m long) have lost around 50% of material.

 

[TugboatEng]

A couple of things, First, there is a platform that the beam sits on which will pool water and cause corrosion. There are also fasteners and hardware which could break the coating. It's closer to the hillside so there is more moisture. It's in a more difficult location to paint. Once the coating fails it exposes more edges so the coating failure will speed more quickly from that point.

 

[Sergey_]

Thanks guys, most likely we will go for the partial replacement of the affected section. Any advise on what could be done (a cost-effective solution) to minimise corrosion there in the future? The only thing which I can think of would be use a proper coating system and seal gaps between the ends of the beams and concrete (both walls and podium).


I will also discuss the option of replacement by treated timber with the project engineer.

 

[r13]

Sorry to have missed the steel beam in my first read and response. Your beam is not the worst I've ever seen, but pretty bad, and can cost more to repair than replace.

The repair depends the condition of deterioration. If it is limited to the support region, and
a) if the flange remain in decent shape with minor section loss, then you can provide flitch plates from beam end to the solid/sound segment. The flitch plates shall be fitted to bear on the flanges using filler or weld.
b) otherwise, cut the deteriorated segment, and connect an identical beam segment, either by butt weld (preferred), or connected by splice plate.

The repaired beam should be seated on a chamfered grout pad to allow water to escape. Please consult with a knowledgeable person (ideally a corrosion engineer) for methods and materials for pre-task cleaning, pin holes filling, surface preparation, and painting.

 

[r13]

Is this a service platform near coal yard? If so, watch out for chemical attack.

 

[Dhurjati Sen]

Sergey, you are right.

Its a typical poor coating aplication issue.

It seems you get lot of rains there.

DHURJATI SEN

 

[LittleInch]

I'm wondering if those ?galvanised? knee supports have been busy corroding the ends?

But mainly I suspect you need to follow the water trail.

Why are so many of those wooden beans sistered to the existing?

But I hate Ivy as well so that will not have helped and would have created a nice humid atmosphere.

All in all a pretty scary looking structure!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sergey_]

Yes, the supports are galv, and I also suspected them, but my understanding of galvanic corrosion is that the zinc coating on them should corrode first before the steel starts.

Also yes, that is New Zealand, so the climate is quite wet here.

 

[TugboatEng]

Those galvanized supports were added after the corrosion happened. That was a repair attempt.

 

[Sergey_]

That totally makes sense, I just was confused by the immaculate state of the brackets.

 

[Jacob_korrosion]

It seems like you might have an issue with Galvanic corrosion since the screw and nut seem to be a different alloy than the actual beam. Make sure to either galvanically isolate the metal parts by isolation layers. Or choose the same alloy for both the beam and screws etc.

If a lot of coating damage is expected, I think I would not use paint or coating since you would only concentrate the corrosion to the damaged areas.

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https://korrosionsgruppen.se/en/products/sacrificial-anodes/

https://korrosionsgruppen.se/en/zinc-anodes/

https://korrosionsgruppen.se/en/aluminium-anodes/hull-anodes/

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