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Beam Repair - Welding

Beam Repair - Welding

Beam Repair - Welding

(OP)
I am looking at an existing beam which has a couple angles welded to the bottom flange. The beam is fixed-fixed as it is welded to opposing tank walls. The beam is A36 steel and the angles are A304 or A316 stainless. According to the client there was burn through when the angles were originally installed (2-3 years ago). From there corrosion made things worse so there really was no fracture just burn through and corrosion. they would like to patch the beam as opposed to replacing it. I'm wondering if in welding the 'patch' there would be issues with thermal stresses causing a fracture and maybe there was no 'burn through' with the original installation. Any thoughts on this?

Thanks!

Sketch:
http://files.engineering.com/getfile.aspx?folder=8...

Photo:
http://files.engineering.com/getfile.aspx?folder=b...

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

What is this beam supporting?

RE: Beam Repair - Welding

(OP)
It is supporting a net/membrane from the angles. Beams are about 3' oc and 8' long. Loads are fairly small.

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

So the angle in continuous under the beam, and a photo taken on the opposite side would look similar to the photo you posted?
Your sketch indicates that this burn through/corrosion crack happened on both ends. Did it happen to both sides of both ends?

There are a couple things that seem strange to me:
1) If it's a fixed connection, you should have compression in the bottom flanges at the ends. I`m surprised to see so much separation. Do the calculations work if you consider it pinned?
2) In the photo, it seems like we're looking down on the top of the fillet weld. I don't see how this would happen with proper weld fusion...
3) There are no other signs of corrosion in the picture.
4) It's easy to believe that a welder made a mistake and burned through in one spot, but for it to happen the same way in 2 (4?) spots make me think there may be something else going on.

As Pitt asked, what's it supporting now?
Why does it need to be repaired? Are you adding new load to it?

RE: Beam Repair - Welding

As Once20036 mentioned, at the ends of the beams the bottom flange should be in compression if this is truly a fixed-fixed beam. With That much separation it makes me think otherwise. Also, the "burn through" seems to be too uniform and for that. Especially if this is at every angle connection.

RE: Beam Repair - Welding

(OP)
Yes this, crack/corrosion has occurred at a few beams on both ends. Some are not as bad as others. There are some other spots of corrosion along the beam top and bottom flanges although that is as bad as the previous photo.

I was/am suspicious about this being "burn through" as well. It seems like there is something else going on. Is there a welding procedure for stainless steel to carbon steel? Maybe it was not followed. Also I don't believe they applied any touch up paint, etc. after the weld

Quote:

1) If it's a fixed connection, you should have compression in the bottom flanges at the ends. I`m surprised to see so much separation. Do the calculations work if you consider it pinned?
Yes, although I'm wondering if they are accurately describing the system it is supporting.

Quote:

2) In the photo, it seems like we're looking down on the top of the fillet weld. I don't see how this would happen with proper weld fusion...
That is correct we are looking down.

Quote:

3) There are no other signs of corrosion in the picture.
Attached is a picture of the other corrosion. Apparently there is a lot of water and aeration that flows around the beams.

Quote:

4) It's easy to believe that a welder made a mistake and burned through in one spot, but for it to happen the same way in 2 (4?) spots make me think there may be something else going on.
That's what I'm wondering as well.

Quote:

Why does it need to be repaired? Are you adding new load to it?
They are not adding new loads, but don't want the beams to fail. It appears that they don't actually even need to engage the flange. I'm wondering if I could specify some sort of patch. Would there be a concern due to the thermal stress of the new weld and the restraint at each end?

Beam Flange Corrosion:
http://files.engineering.com/getfile.aspx?folder=9...

Looking up at heel of angle (corrosion but no fracture)
http://files.engineering.com/getfile.aspx?folder=3...

Fracture at a different location:
http://files.engineering.com/getfile.aspx?folder=3...

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

Rfreund:
I’ll bet that is a fatigue type crack, at an inferior weld condition which would have been done overhead (out of position), btwn. the W shape flange and the toe of the angle. Dissimilar metals and maybe incorrect welding rod used. Could not get good welding rod orientation because it was close to the tank wall. Then, the W flange is pretty much fixed at the tank wall, but the angle is being loaded so it tends to twist the W flange. That is, the angle is pulled down on one end and then the other, so it is constantly yanking down on one flange tip and then the other. The shape of the crack you showed in your first photo is not a burn through indication, it is a fracture crack. They did the down hand weld shown in your first photo, and carried it around the toe of the angle, and into a weld btwn. the angle toe and the bot. of the W flg. It looks like they didn’t get any fusion btwn. this weld and the bot. of the W flg. I think you can see the top of the horiz. leg of that weld in the crack, as if it never melted into the bot. of the W flg., just globed on the W flg. surface and froze. Additionally, when they wind a weld around a corner/corners like this (the angle toe edge and the W flg. edge) they are very likely to leave a notch or nick in those edges, which is a stress raiser, or crack starter. And, that notch on the W flg. is where the crack started and grew from.

RE: Beam Repair - Welding

No expertise claimed here.

The photos suggest that the tank is open- topped, rectangular, longer than it is wide,
and that the bottom flange of the beam may be subject to some tension from
hydrostatic pressure trying to belly out the sides, in addition to whatever loads
are applied to the angles.

The top edge of the tank appears to be reinforced by an angle or band welded to its exterior surface, and the actual tank wall appears to rather thin, maybe 1/4" or so.
... else explain the nice weld bead running parallel to the wall in IMG_0724.

... or maybe I am misreading the photos.



Mike Halloran
Pembroke Pines, FL, USA

RE: Beam Repair - Welding

(OP)
@DH and Mike - Great Suggestions, thank you. Mike you may be correct in you assumptions of the thin plate. I actually could not verify the thickness due to coverings and such around the tank. I think the issue is a combination of you suggestions.

Now time for me to think of a repair. The beams, as I've been told, have performed well in the past. However the issues occurred when the angles were added. I guess the big question is, should they remove the existing beams, hmm...

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

I'll also through a cautionary guess at fatigue combined with a poor weld caused this. Corrosion obviously didn't help either.

If this is a place that is readily observable and not too costly to get at again for a repair I would just drill the end of the crack, grind a nice V profile in the crack, install a backer bar and CJP groove weld it. Grind off the backer back and smooth down the weld and you're good to go. Advise them to monitor the crack for a few years and, if the crack doesn't reappear, then you're good to go.

If this needs to be a 100% solid repair right now then perhaps a reinforcing plate is in order.

Maine Professional and Structural Engineer. www.fepc.us

RE: Beam Repair - Welding

Is there any chlorine in the environment?
as said above, this is a dissimilar metal weld, where wrong filler metal might have great affect on the properties of the weld.

if you repair, make sure to grind out all affected (by dilution) base material.

RE: Beam Repair - Welding

Mmmm, good point kingnero; a wrong filler metal or improper weld procedure could have been used causing a poor weld. If that is the case then redoing the weld will definitely result in improved performance.

Maine Professional and Structural Engineer. www.fepc.us

RE: Beam Repair - Welding

(OP)
Good points again.
It appears that E70 is an acceptable filler metal for stick (SMAW) which I'm *guessing* is what they did, but maybe not. Is there a better filler metal to be used or procedure?

Thanks.

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

Nope, certainly not for carbon steel to austenitic stainless, like here. 309 would be a good place to start, asking a welding engineer would be even better.

The above is typically what you get when one doesn't know what he is doing, and I mean certainly no disrespect to the weldor who did this.

RE: Beam Repair - Welding

(OP)
Kingero, Ah yes I see now. I think 309L should have been used. Again I'm not sure what was used, but could an E60 or E70 mild steel electrode cause "heat crack"?

I'm sure they would be fine with the grind and weld solution, however the cracks are right at the toe of the angle/fillet weld connection. I"m not sure how they would do that. Could they remove that fillet weld, I'm still not sure how they go about reattaching things then. Some of the "V's" will be pretty wide. hmm..

thanks again for the comments.

EIT
www.HowToEngineer.com

RE: Beam Repair - Welding

I'd like to see the welds connecting the angles remedied in addition to the flange crack. Given the effort involved, and the light weight of the pieces, I wonder if it might be easier to have a new setup welded together in the shop.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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