Corroded Steel Beam Repair

[CN-EIT]

For starters, I have referenced this prior thread Link.

Existing design criteria:
1) Ex. 21WF62 A36 Steel Beam.
2) Beam is 18'-0" long simple span with standard shear connections to supporting girders.
3) Beam is non-composite and carries a 4" thick concrete slab.
4) Design loads are DL=25psf (superimposed) & LL=200psf (industrial use)

Context: Beam supports industrial equipment. Originally, the center third of the beam supported equipment which produced a liquid that corroded the beam. The end thirds of the beam did not have equipment but are also corroded.

Corrosion summary:
1) Center Third-

-Web: uniform pitting corrosion ranging from 1/16" to 1/8" material loss each side of web​

-Top Flange: loss of flange thickness & width from 3/8" to entire flange thickness and 50" reduction in flange width: top of flange was visible.​

-Btm Flange: Consistent and uniform pitting from 1/8" to 3/16" material loss on top & bottom surface of flange​

​

Top surface of btm flange shows portions of delamination from the edge of flange into the fillet (k) region of the beam​

-Web/Flange: localized portions of steel delamination​

2) End Thirds-

-Web: uniform and consistent pitting corrosion ranging from 1/16" to 1/8" material loss each side of web​

-Top Flange: uniform and consistent pitting corrosion ranging from 1/16" to 1/8" material loss bottom side of flange, top side of flange not visible, though flaky material was able to be chipped away at locations where concrete slab had not entirely concealed edge of flange. Flaky material appeared consistent with portions of exposed flange at center third where delamination/corrosion was observed.​

-Btm Flange: Consistent and uniform pitting from 1/8" to 3/16" material loss on top & bottom surface of flange.​

The concrete floor has only been removed over the center third. The area does not currently have design surface loads or equipment, only the concrete slab. There are 10 of these beams in total. Given we are halfway through the plant scheduled shutdown, schedule is a concern and as such repairs, not replacement of, of the beams is desired.

The attached is a sketch of what I have in mind, basically plating the entire beam. Where we have near total loss of structural cross section at the center third, the plates would need to take the entirety of the load; essentially a 6'-0" long splice that needs to develop the forces back into the end thirds of the beams which would carry it to the existing connections (ex. connections are not corroded). Before we go down the "just replace the beams" line, there are substantial impacts to surrounding area trying to replace these beams, that is a last resort in this instance.

What I am looking for:
1) General thoughts and concerns on the detail.
2) Required surface prep to actually accomplish sound welds.

My thought is, to actually develop the forces out of those plates and into the end third of those existing beams, they would need to grind down all of the pitting corrosion down to a smooth steel surface. There is foreign material (source of corrosion) sitting on those flanges, chipping it away showed that the steel was moist/wet under it, in addition to the grinding, would these beams need to "dry out" prior to welding to prevent continued corrosion?​

3) Shear flow, and where to start with that. Resources on that are welcome.

 

[jayrod12]

I'm going through this currently on a industrial project. Plant shut down starts in a week so I'm just a bit ahead of the game. We originally were looking at reinforcement and re-coating of the beams but after review of all locations and extent of corrosion we've determined that removal and replacement is actually faster and therefore cheaper. The cleaning, welding and coating is expected to take longer and need higher wage people to complete it. Replacement essentially requires labourers. The shoring requirements for us are the same so they aren't saving anything there.

 

[CN-EIT]

@jayrod12:
The cleaning (surface prep), welding, and re-coating is a part that I am also looking at. I am not sure what type of surface prep would be required to even achieve a sound weld given that the beam is pretty uniformly corroded. I've identified four primary forms: deposit attack, underfilm corrosion, pitting, and intergranular corrosion (delamination) with all but the last along the entire length of the beam. It seems to me you'd have to grind all of that corrosion away to even start the repair; which to your point, is a time-consuming process.

edit: additionally, not being able to observe the entire top flange leaves me a bit nervous since this flaky "slate" like deposit which was observed at the exposed portions, was observed in locally from the underside of the slab between the steel beam and the concrete slab. That would indicate to me that the delamination has potentially propagated outside of that center third.

 

[jayrod12]

That flaky intergranular corrosion of the top flange is almost precisely what we're fighting. And it's also in an area that's relatively inaccessible so I was having a hard time believing the contractor could get into the space to clean appropriately and then provide the reinforcing etc.

It's much quicker for them to chip out whatever connection exists between the slab and beam, if known, and replace the entire beam length. Then the replacement beams can be pre-fabricated to length to match the existing connections. My one issue I'm having on mine is there are a couple locations where the column is compromised as well. So we're trying to figure out how we can accommodate that readily if it's determined to need replacement/remedial action. Due to the location in the plant, we aren't able to do any sort of investigation until plant shut down so we're stuck with visual observations only.

 

[EdStainless]

You are not going to be able to weld unless you solid, clean, dry metal.
I think that repair is a fool's errand.
Replacing will be faster and more reliable.

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

 

[SlideRuleEra]

CN-EIT - You say the connections are ok, what is the condition of the web and top flange near the connections... say the last 2' at each end of the beams?

 

[CN-EIT]

@jayrod12:
I appreciate that you are experiencing similar issues with delamination. That was the first time I had seen it in the field and it is quite an interesting form of corrosion. I agree, replacement at this point is most advisable.

@SlideRuleEra:
The web near the connections appears to have experienced both general corrosion and mild pitting. The top flange was obscured by the concrete slab and as such was not able to be thoroughly investigated (see comment about characteristics of delamination being locally observe from the underside of the slab). That being said, based on multiple spot checks of multiple beams, I am confident that at a minimum there is some form of corrosion along the length of that top flange near the connections. The connections are double angle shear conns with 5 bolts to girder and welded to corroded beam. Underfilm corrosion appeared to be present at the connections themselves, however the angles and welds both appeared to be in good condition.

 

[SlideRuleEra]

CN-EIT - Since the web is deteriorated at the connections, I have to agree with others... replace the beams. Repairs could be made if there was some decent existing steel near the connections to work with, but that's not the case.