What type of steel is this? 4

[cookyb]

I've got a building built in 1993 that was built using (reportedly) recycled bridge steel (don't know when the bridge was built). We are doing a remodel and are having some trouble welding to the existing wide-flange beams (cracks have been visibly detected at all of the welds so far). I had them sample a couple of the flanges to have a chemical analysis done so we could try to determine exactly what type of steel we have and develop and weld procedure. It's a 3-story building and samples were taken from the bottom flanges of random beams at each level. After the analysis, the testing firm reported that there were actually two types of steel being used, 1018 and 1020 steel. Attached are the test results.

As you can see, there are a couple of other chemicals floating around in the steel sample as well. The testing firm, who is also acting as the CWI, tried a test weld by preheating the sample to 225 degrees F at approx 3" from the weld. During their bend test after welding, the sample cracked and broke in the preheated portion of the sample, not at the weld, and at not much of a bend angle either (see pic).

Are these results indicative of 1018 or 1020 steel? Has it been carburized and that's what is causing the welding difficulty and extra chemicals? My main issue is developing a weld procedure for the old steel. So far the testing firm has tried preheating and welding with a flux-core wire feed.

Any ideas?

 

[cookyb]

Flux core. I'm not sure about the AWS classification.

 

[DeleteriousPhases]

hmm, i'm not sure i'd use flux core to weld these. stick buttering is a good suggestion. I'd use 7018 the whole way if possible.

i feel that you could probably monkey with the weld geometry to prevent the weld from pulling across the rolling direction to prevent the suspect laminations from giving away.

surface preparation before welding (light grinding, wire wheeling) to remove oxides, dirt and other crap, and prep the joint for welding is key. if surface preparation is the issue, also check holding oven temperatures for low hydrogen stick electrodes (7018). if they're out of the oven four hours they're no good.

 

[weldstan]

Self shielded E70T-4 or E70T-11 and their like should not be used for these welds.

 

[cookyb]

I'll pass this along. They are going to try a test weld tomorrow and MP test it. I'll let you know how it goes. Thanks!

 

[cookyb]

Weldstan/DeleteriousPhases,

Are you saying flux cored welding shouldn't be used for this type of welding, or you wouldn't use it knowing what we know now after all of the testing we did? The GC is going to ask for more time/money because he said he bid the job for wire feed welding. I don't want to screw him over, I would just like some input on whether wire feed should have ever been considered, and what's the actual time difference we are looking at.

For any of you still following, the MP test on the root weld and the final weld both passed and the SI is going to do a VI after 48 hours as well. The ended up grinding the surface of the steel and using E7018 electrodes. Thanks for all of your help on this one.

 

[weldstan]

I have not stated that FCAW should not be used; only the self shielded wires as stated. These wires and similar have not been able to consistently pass bend tests at ambient temperatures up to nearly 100F. They have very poor toughness. They are not low hydrogen filler metals.

 

[cookyb]

Gotcha. What about the speed of the welding? The GC now wants 5x more $$ for the welding portion of this work. This seems high to me, but I'm not a welder.

 

[weldstan]

What process is he now using? SMAW? In the field, they will be lucky to get deposition rates greater than 1 to 1.5 lbs per hour with SMAW and E7018 electrodes versus up to 5 lbs per hour with FCAW with E71T-1 electrodes.

 

[racookpe1978]

1.5 pounds per hour in the field for SMAW (Stick)? Should be 1 rod per minute once they actually get started in place, even in the field. Allow 3/4 working rate though.

Figure a 7:00 am "payday start. If on a bridge scaffolding or deck, "maybe" 8:30 when the first rod is struck.

 

[weldstan]

With proper supervision, I would agree that greater productivity can be obtained with low hydrogen SMAW; however, left on their own, don't count on much more than was stated. Going to lunch - 1/2 hour to lunch area and 1/2 hour back. Getting more electrode from Rod Room - 1/2 hour going and coming. Smoke breaks. BSing intervals, interpass cleaning time, etc., etc.

 

[cookyb]

Ha ha! All true.

They started with FCAW and the welds were visibly cracked. So, they took a couple of coupons, welded them up using the same process (but they preheated this time) and the welds failed the bend test. So, now I've had them grind the existing weld surface clean and weld the tubes up with low hydrogen SMAW. This way passed the MP tests and the VI. Now the GC is asking for more money because he said he bid FCAW and SMAW is going to take a lot longer. Our specs say weld per AWS D1.1 AND use E70 low hydrogen electrodes so I think we are covered on that.

Does anyone know if the procedure for FCAW overhead is prequalified? I didn't think it was.

 

[weldstan]

FCAW procedures can be "prequalified" if Constant Voltage power supplies are used.