Sudden Rash of Transverse Weld Metal Cracks 4

Carburize;
This sounds like hydrogen embrittlement related to the weld wire/flux. How was the wire stored? Is the problem related to a specific spool of cored weld wire??

I am checking the wire batch history as you suggest

How is the wire stored and kept clean and dry?
How are weld joints cleaned prior to weld?

Picking up a little moisture could give you some H issues.

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Corrosion never sleeps, but it can be managed.

Wire coils are kept in their original packaging on shrink wrapped pallets close to the welding stations. Base materials are machined or sand blasted prior to welding.

Maybe it's because winter is coming? A drop in temperature can render customary preheat practice insufficient.

Hg

Possible, possible but here in the south lower fall/winter temperatures usually mean lower humidity compared to the 95% in summer!

Preheat isn't just about humidity, it's also about temperature differential and cooling rate.

I'm in the south too, and we'll find fabricators not preheating in the winter because most of the year they don't have to and they just forget the whole concept. Or they don't realize that they have to heat more once the temperature drops.

Hg

Carefully gring into the weld metal looking for slag or even unfuzed flux. I have seen cases where the the welder trapped slag within the filler using when the welder in pushing the heat input of the process. Also do a weld chemistry test, if you can compare an older batch and newer. Pay particular attention to the Nickel content. The Nickel content should be 0.50%wt. Note I have had cases where the wire manufacturers have lowered the Nickel content, while still meeting the code requirements, to reduce the cost. Resulting in cracking, during welding.

Check the purity of the shielding gas. Is the welder purging the system priotr to welding?

That's a good point--especially in today's weird metals market, the ingredients of the wire will change, not just because of deliberate reformulations on the manufacturer's part but because of changes to the nature of the scrap content in the strip used to make the cored electrode, etc. Get the wire manufacturer to give you some recent chemistries vs. their published "typicals".

Hg

Carburize;
Possible solution to your problem - order replacement flux core wire as SFA 5.20 E71T-1H8. The H8 is a hydrogen designator that specifies the maximum hydrogen level in the flux core wire.

Keep in mind that 99% of the time transverse cracks are related to dissolved hydrogen in the weld deposit. Purchasing new wire is the quickest way to verify your problem. Preheat will only help to reduce thermal stresses and reduce the level of restraint. The problem is that dissolved hydrogen reduces the ductility of the weld metal during solidification. Any subsurface cracks open up during PWHT.

Agree with metengr. Had a similar transverse cracking problem, observed after PWHT, and they were absolutely caused by hydrogen.

You may also wish to check the deposited weld metal chemistry for a high Carbon Equivalent. It has not been that uncommon to find "out of spec" filler metals.

Here are several photgraphs of some fluxcore weld cracks (August 2004) Filler E81-T1 Ni1. Are these similar to your cracking situation?







Is there a reason why you are using the E71T-1 in lieu of E70T-1? The quick freeze slag might be causing problems. With the E71-T-1 product the torch angle is much more important than with the E70-T-1 product.

The transverse cracks are just like the one's in the third image although lots more of them. Some welds had them every inch or so along the bead.
No particular reason for the choice of wire - we have been using it very sucessfully since 1996 this is the first time I have observed any major problem with this consumable.

Rich2001
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StoneCold

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If you are getting cracks in the weld metal and not the base metal, then we need to look at the possible embrittling mechanisms for the weld metal.

Hydrogen is usually the biggie. The best way to avoid hydrogen cracking is to avoid hydrogen, but if it is already there, the tendency to crack from hydrogen can also be addressed with preheat. This helps in several ways. It reduces the moisture available from the base metal, if there was any there to begin with, it slows the cooling rate, which produces a more favorable microstructure to resist cracking, and it gives any hydrogen present more time to diffuse out of the weld. It can also be addressed by post-heat. That is keeping the weld hot (usually 500-600F for 4-12 hours) after welding, or until PWHT.

Another factor that contributes to the tendency to crack is base metal and weld hardenability, which is related to their chemistry and thickness. The thicker the base metal & weld, the higher the cooling rate for a given base metal temperature (up to about 1 1/2"). The way to compensate for thicker base metal, is- you got it- more preaheat. As mentioned earlier, filler metal chemistry can also contribute if the carbon equivalent gets too high. A higher preheat help with hardenable filler metals too.

High joint restraint is yet another way to cause weld metal cracking. Thick plates or welds create tri-axial stresses in the weld, which if the weld is not tough enough, will cause cracking. This can be helped with preheat also, in order to reduce the residual stresses.

In a small number of cases, PWHT can also cause embrittlement of the weld metal enough to crack. This is the last of the reasons for cracking I would look at, but it is a possibility. Some manufacturers of E71T-1 add elements such as Boron that help with as-welded toughness, but can seriously degrade toughness after PWHT, depending on time, temperature, and amount of the additions.

Also, Per AWS A5.20, the limit to Ni in E71T-1 is .50% max. I do not think many manufacturers intentionally add Ni, as they can obtain the required toughness without the added expense.

Thanks for all your comments - I suspect that hydrogen may be the main factor. Other than minor changes in the ambient temperature and humidity within the building everything is constant, type of joints, thickness of parts, base material, welders etc. My focus right now is on storage -although the flux cored wire is reasonably well wrapped and "reasonably" resistant to moisture pick-up it looks like the coils which may have given the problems were stored for the longest time and were the coils closest to the floor.

In your quest to locate the hydrogen do not forget to examine the shielding gas system. The gas itself, the tubing connecting the regulator to the wire feeder/gun. This tubing routine gets small holes due to weld spatter, grinding filings, et cetera. While the gas in the tube has an overall positive pressure, the difference of the partial pressure of the water vapor between the ambient air and the shielding gas will cause the water vapor to migrate into the shielding gas from the ambient air.

This is the same reason why the first two or three feet of the flux core wire should be removed before use at the beginning of the day.