Welding of Highly restraint joints between structral members having CE 0.47% in a process module

[adyard]

We have experienced some weld HAZ cracks in the structural welds with high restraint in our ongoing Process modules structure.
We found high Carbon Equivalent (CE= 0.45 to 0.47%) on some beams (W-sections) W14x16x193 used for columns which are being fillet welded with A36 stiffeners and CJP welded to A992 beams CE</=0.43%) by moment weld/shear weld connection. We are finding cracks in HAZ of high CE members. Presently we are welding with E7018-1H4 , with preheat 115 Deg.C minimum.

Anybody have experienced with this kind of HAZ cracks? If yes, please share your experience and how to weld these joints and achieve crack free welds.

 

[EdStainless]

Are all surfaces well ground and solvent cleaned?
If these welds are that highly restrained you may need to be looking at alternate methods.
Sounds lime more preheat is in order. I don't have that ref at hand so I'll leave that for some of the experts.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Are the cracks transverse to the weld region or parallel? This is very important because transverse cracks can be from restraint or higher preheat is needed. Although, your 115 deg C preheat seems reasonable.

 

[adyard]

[img

https://res.cloudinary.com/engineering-com/image/upload/v1461851882/tips/IMG_7677-1_txdwl2.jpg

The cracks are not transverse to the weld regions but are parallel. The cracks resulted in HAZ only. The HAZ of the High CE member.
See attached pictures.

 

[metengr]

Increase the preheat and soak area size in the high CE member to 150 deg C and twice the current size, respectively.

 

[adyard]

Thanks metengr. It should help if we increase the preheat soak area.
The soak area size for preheat we are maintaining is 4 inch. minimum on either side of the joint.
We are presently preheating with propane gas burner. The preheat some times even recorded to 150C. Still then the HAZ cracks appear randomly. What about restraint? How to overcome the effect of restraint acting on the joint? Any ideas about stiffening the joint until the welding completed and cooled to room temperature to mitigate the effect of high restraint??? just a thought.
See the picture of the HAZ crack.

 

[metengr]

Thanks for the closer follow-up picture. It appears you are getting cracks along the weld toe in the high CE material, similar to underbead cracking. I don't believe this is a restraint issue, I think your preheat soak time is inadequate. Typically, cracks confined to the weld toe region are caused by lack of preheat in hardenable base material. I would increase the preheat to even 200 deg C and make sure the soak time at temperature is at least 15 minutes and not weld once you reach Tempel stick temperature. You would be surprised at how much heat is wicked away from the weld region.

Also, if you can did you run a chemical analysis of the high CE material? This material could have residual elements that pose a weldability problem.

 

[weldstan]

Weld sequencing, properly done, can also mitigate cracking with the preheat used or somewhat higher.

 

[adyard]

Thanks metengr for the analysis as Underbead cracks. Thanks Weldstan for pointing out the weld sequence.
The preheat of 200C should be of more help. Right sequence of welding of joints.
Metengr, I still have concern about the restraint acting on the joints, why because these cracks are resulting in welds attached to the columns which are of 13mtr height but no much happening on small stub column welds, equipment frames welds.
See the attached picture of kind of module this is and how many welds the column having at every elevation.
The members welded on all four sides and stiffener in the column under every weld.

These under bead cracks are happening in simple fillet welds of stiffener plates inside the columns (W14x193 where flange thk 36mm)

Appreciate your comments/thoughts on
- Post heating of 250-315C will be of any added help apart from 150C preheat
- High heat input will be of any added help
- welding with higher dia. electrode like dia 4.0mm only for higher heat input
- Preheating and post heating with electric coils/mats instead of burners- though it is very difficult on the kind of joint configuration, but we can make it.

 

[metengr]

Using elevated preheat (200 deg C) with resistance heating coils will help significantly to keep the weld region warm before welding. Beyond this and weld sequencing as mentioned by Weldstan, I think you have covered it. I don't see the need for post weld bake at 250 to 315 deg C. The elevated preheat I prescribed will be high enough to prevent possible delayed cracking. When I had situations where joint restraint was a problem, elevated preheat solved it.

 

[adyard]

Agree that the elevated Preheat of 200C will take care of restraint.
How about the CE=0.47 combined with high restraint. Is this 200C still take care of "to avoid high HAZ hardness".
We experienced around 430 HV10, 450 HV10 in HAZ of high CE beam when we cut and tested a production weld macro section.

 

[metengr]

This so-called high CE material sounds more like micro-alloy steel. The elevated preheat will help to reduce peak hardness values, which you reported are high. These values need to be around 400 or less.

 

[dhengr]

Adyard:
Are you using welding consumables with high alloy content, which tend to concentrate the hardening alloys in each successive pass? Maybe using a slightly softer weld metal, if you don’t need the weld metal over strength would help soften things up a bit, along with the higher pre-heat and interpass temps, and along with a slower postweld cooling.

 

[adyard]

dhengr:
We are using E7018-1 H4. Hope this would be softer enough for the material A992.
Initially we have used E71T1-C H10 and later we stopped FCAW as this diffusible Hydrogen content of max H10 can be one of reason for this cracks.

 

[adyard]

metengr:
Appreciate your analysis on this cracks (shown in the below picture) resulted in type of weld.
Why high CE column flange to beam web Fillet welds have no HAZ /underbead cracks(is because of no restraint????)
Why simple stiffeners' fillet welds inside the high CE column have HAZ/Underbead cracks (is because of restraint???).
Had a doubt about T-fillet joint fit-up where we usually maintain gap of 0mm to max 1.6 mm gap between the members; but sometimes it goes to 2.5/3mm. ---- will it be a stress raiser adding fuel to high restraint / high hardness resulted in high CE member HAZ?

 

[metengr]

The additional picture with the locations of the cracks is helpful. Because of the consistent perpendicular orientation and location of the cracks on the column web and flanges I am thinking that you may want to try and use partial penetration groove welds in lieu of fillet welds to join the stiffener plates to the column. It may well be that the higher strength column and weld configuration is not accommodating weld shrinkage. I also considered lamellar tearing.

Try and bevel several stiffener plates on each side for partial penetration welds using the elevated preheat and heating methods we discussed above and sequencing the welds.

 

[weldstan]

Lamellar tearing could be an issue here. When you attempt to repair determine if cracks extend well into the base metal. If lamellar tearing is determined, butter the affected area prior to making the strength weld. Check the material for stringer sulfide inclusions.

 

[dik]

Is the Sulfur content an issue? Can cause hot short welds?

Dik