Rewelding on 4140 material Rotek slew bearing - previously welded

[cooletti]

What considerations should be looked at when rewelding on a 4140 4' dia. steel slew bearing that is being relocated from one drill rig to another?
Concerned that the heat effected zone on the initial weld on the bearing metal has made the area too hard now. Will be testing its brinell hardness soon. Are there limits on the hardness for re-welding?

I am not a welding engineer and need some advise.

Thank you

 

[metengr]

cooletti;
Can you provide any details as to how the welding was done (process), the amount of weld metal deposited, was preheat or stress relief was performed (temperatures)? Was nondestructive testing performed after welding?

The reason I am asking the above questions is to help you with a better response.

 

[cooletti]

Yes. this is the problem. We have been asked to consult on the new welding and install. The old install and its weld process was done 4 years ago and there are no records. No NDT was done either that I am aware of. Rotek brg company advised/ had them preheat to 400 deg with a rosebud. Thermal blankets used after welding to slow cooling.

Where should i start? NDT services I assume.

 

[metengr]

Here is what I would do given what you know already;

1. Perform a surface NDT of the area or region to be welded. I would clean up the surface and either perform a wet fluroescent MT or Liquid Penetrant inspection.

2. If the NDT shows no reportable indications, I would re-weld using a qualified welding procedure and welder.

3. Preheat is a requirement for this base material, and it should be controlled using electric resistance heaters. Suggested is 450 deg F, minimum.

4. At this point, what are you welding on the slew bearing? Are you performing a weld build-up?

 

[cooletti]

I agree...will hire NDT services.

Will be setting up a QWP and welders onsite are prequalified. The 4140 bearing( 1 1/2" thick ring) will be welded to the truck frame - 3/4" mild steel

I see in my AWS welding handbook that the tensile strength on 4140 drops significatly as tempering temp increases. (250 ksi to 180ksi)

Any thoughts on this regarding the heat applied to it from prior welding. They claim they put 5 passes of E70- rod on initial install.

Thanks for all your valuable input...much appreciated!!

 

[metengr]

Most likely fillet welds were used to secure the bearing to the truck frame. Without knowing the specific heat treatment condition of the 4140 bearing ring, the heat from welding will effect mechanical properties.


To avoid all these problems, why can't this bearing ring be bolted on to a manufactured collar that is only welded once to the truck frame? There has got to be an easier approach than welding, cutting, re-welding each time.

 

[MikeHalloran]

Does the old rig have any salvage value?

If not, maybe you can (abrasively) cut the affected area out of the old rig frame, and bolt it to the new rig.



Mike Halloran
Pembroke Pines, FL, USA

 

[Guest102023]

Sounds like the weld will qualify as structural and not just restoration. That would be a no-no for 4140.

 

[cooletti]

It does have bolts in it also, but the owner of the company wants to weld the bearing down to the chassis also. They have had prior slew bearings brake free from the truck....thus the additional welding requirement.

 

[metengr]

Well, after thinking about this even more I am absolutely convinced I would not risk welding again or even welding this bearing to the chassis because the heat from welding will effect the inner race mechanical properties and cause failure. I would take my chances and use a more rugged collar/flange design with larger bolts, if necessary.