Repairing Corroded Steel Structural Beams

[ONT003]

I've been tasked to address a corrosion and possible material loss issue on some structural steel in an aircraft hangar. These beams have been exposed to salt and moisture from the bay. There is bubbling under paint on the beams, corroded rivets and some concerning corrosion at the base.

I've attached photos. My first instinct is to blast clean the damaged areas, treat the metal, possibly fill any pitting and re-coat. With the level of corrosion visible on the base of the I beam, is it recommended to also install a cover plate for reinforcement?

Any recommendations are appreciated. We lost our Structural Engineer recently so if the level of repairs require structural engineering design we'll just have to contract out support. Thank you.

http://files.engineering.com/getfile.aspx?folder=d97a2b0d-beeb-4809-89f7-24b54bb19861&file=011.jpg

http://files.engineering.com/getfile.aspx?folder=c6312adb-4780-45fa-92d0-bf751a465033&file=007.jpg

http://files.engineering.com/getfile.aspx?folder=a0974917-642e-4ee4-9ef9-bd941ea58cc4&file=019.jpg

 

[Lomarandil]

Yes, blast and re-coat is generally the most common course of action to stop the current corrosion. Do you know if the current paint is lead-based?

I wouldn't be concerned about the corrosion on the rivet heads, as long as there remains a decent "mushroom cap" after cleaning. (Maybe not even then, there's debate about the value of the rivet head vs the shank, but that's getting into structural engineering).

Based only on those three photos, I wouldn't be overly concerned about the section losses you're dealing with. They don't look very substantial to me (pre-blasting, at least). (Of course, this is presuming that you aren't also dealing with additional design loads imposed over the years.)

The base of the I-beam may be tricky. It looks like the beam is embedded in the concrete -- to what purpose and eventual connection is unclear without additional evaluation. Certainly, installing a cover plate that ends at top of concrete won't do a lot for you.

 

[ONT003]

Lomarandil - thank you for reviewing the photos and providing insight. I'm glad to know the cover plate would likely not do any good. I have been told the beams are embedded 4 feet into the concrete but as of now I don't have as-builts to confirm this. I'll proceed with blast cleaning and evaluate what's underneath. Hopefully we'll just need to re-coat.

These beams do have lead containing paint, so we'd follow the typical abatement procedures. The question is now, blast the entire structural element or just the heavily corroded areas? It's huge!

 

[JAE]

I'd agree with Lomarandil.

For the base, you might have to chip out the concrete around the member to get down below the floor line - and to allow visual inspection.

I've seen situations like this where the rusting essentially terminates within a 1/2" or so below the floor - perhaps due to lack of oxygen.

This allows you to blast the lead paint away clear of the rusted areas and get a good bond beyond the rust edges.

I'm not sure how effective just cleaning and re-coating numerous isolated areas would be in the long term. If the goal is to get a 20 year life out of this then perhaps a more comprehensive coating is required.
If they are looking at 5 years - then maybe strategic coatings would work.

That rivet head does bother me a bit. I think Lomarandil's view is good - just seems like the head was flowering out a bit. I think I heard once that if you hit a rivet head with a ballpeen hammer and it "pings" then you are good - but if it has a dull sound then there may be an issue....old pre-ASTM test method I'm sure.


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[Sawbux]

I would recommend complete removal of the existing coatings. There looks like there is a lot of corrosion under the coating and it extends beyond what is visible. If you are doing lead removal anyway, maybe you should do complete remediation (if funding allows).

 

[Lomarandil]

Yes JAE, that's an old test method that is still useful. A metallic ping means a sound rivet, duller thud can be indicative of one of a couple problems (which I can't remember). Certainly a good first-pass indication.

 

[ONT003]

Thank you all for your recommendations. I agree with complete remediation and will look into evaluating the beam below the concrete. As well as the rivets, only a few are that badly corroded as in the photo.

Thanks again!