Dissimilar weld on a gear wheel assembly 3

[starflex]

Hi All,

I have to review a welding recommendation (not a WPS, just some guidelines), and I came across two different materials.

It is a gear wheel assembly, around three meters diameter, which is composed by a internal hub (made of carbon steel, 350MPa) and by an external crown teeth, made of 34NiCrMo6 (high strength Q+T).

The two parts are joined together thanks fo a full pen butt weld (double vee preparation): basically, we have an internal "disc" and an external crown (T section), and they are welded together. I hope it is clear.

In the recommendations for fabrication, I found a few things that do not look right.

The circumferential welds shall be full penetration with 15 to 20% reinforcement
WHy reinforcement ? Besides the fact that I do not see any real advantage in doing that anyway, considering that is under cyclic stress condition I would try to make the weld as much planar as possible with the two components.

Thermal stress relieving shall be carried out generally in accordance with the requirements of AS 1210 and in such a manner to ensure residual stresses in the rim are reduced to very low levels.
Well.. this is way too generic, and AS 1210 is the fabrication code for pressure vessel.

But at this point, I have another question. It is a Q+T steel to be joined with carbon steel. I will have an undermatching filler material (Nickel alloy ? Austenitic?). If I go with the austenitic, I cannot even do the stress relieve; I would probably just do the temper beads next to the HAZ .

If I use a nickel alloy yes, I can do the stress relieve (but it would cost way more).

How would you approach the joint ? Any recommendation ?

Thanks in advance.

 

[metengr]

I agree with the full penetration welds and I would make the welds flush.
Regarding the post weld treatment (PWHT), I would perform it and select a temperature that is below the original tempering temperature of the higher strength, Q&T material. You want to take advantage of reducing residual stresses and to temper the heat affected zone on the high strength side of the weld joint. The reference to AS 1210 is probably for PWHT temperature and time guidance.

I would use an undermatching, low alloy filler metal versus nickel-base. Also, you should qualify this welding procedure.

Last, you mention no post weld nondestructive testing (NDT). As a minimum for a gear wheel, I would perform radiograph testing (RT) of the full penetration weld or perform ultrasonic examination followed by a surface examination, like wet fluorescent MT or Liquid Penetrant.

 

[CoryPad]

We do precision welding of alloy steel gears using nickel filler metal without preheating or post-weld heat treatment. We specify full penetration, a maximum reinforcement of 20 %, but do not require a minimum reinforcement amount. We use ultrasonic testing after welding. Some of this may not translate to your large parts (e.g. post-weld thermal stress relief).

 

[starflex]

Guys,

Thank you for your input.
@metengr: Agree with you. Details for PWHT temperature and time are probably souceable from another code. Indeed, the welding procedure shall be qualified beforehand.
Did not mention the NDT, true. I agree with you with th 100% RT and surface. The original specs state MPI only...which is a bit weak.

@CoryPad: what would be the purpose of reinforcement ?

 

[CWEng]

By the 15-20% reinforcement, are they talking about a fillet type transition on the T-joint? If so, this would act like a stress concentration reduction, as it would reduce the notch effect of a sharp corner at the T-section.

 

[starflex]

Mmhh..I do not think that is the case tho...

The only circumferential weld is the one in the attachment, as the external rim, T shaped, is made in one piece..

 

[Tmoose]

By inspection I'd guess the weld is not in a particularly high operating stress area.

Is the gear disk solid, or spoked, etc?
If solid, one of my concerns would be to reduce self-inflicted problems in such a highly restrained joint.

Just from a weld integrity perspective some amount of convexity (reinforcement) is often required.

http://weldingdesign.com/blodgett/concave-welds-avoid-cracking-0709

http://www.lincolnelectric.com/en-us/support/process-and-theory/Documents/weldcracking.pdf

What size is the specified weld?
The % "reinforcement" called for does not exceed the table on page 2 here-

http://www.lanl.gov/orgs/eng/engstandards/esm/welding/vol2/WFP 2-01-Att-2-R1.pdf

Any mention of allowable weld undercut?

 

[CoryPad]

The purpose of the reinforcement (excess weld metal) is to prevent other imperfections like undercut, incompletely filled groove, etc. Those imperfections are worse for function compared to excess weld metal. We do not remove the excess weld metal because we do high volume production and do not want to add cost.

 

[ibfmining1]

Just F.Y.I , I usually develop U.T, as opposed to X-RAY by using straight beam; and 2 additional types of angle beam (45 ; 75 degree); "i.a.w" A.W.S D 1.1 Code. M.T is also developed as per A.W.S D 1.1 acceptance criteria (before and after PWHT). My gears range from 32 to 40 ft in dia. (made in quarters and using full penetration welds between rim (4340) and web (A-36). And "yes" , WPS / PQR is mandatory !

Hope that helps.

 

[starflex]

All,

Thanks for your inputs. The ball is now back to the client, that is selecting the manufacturer (I guess he is in the auditing / surveying phase).

I conveyed all the points discussed here, hopefully they will be useful even if they had a last minute change of mind and they decided to go ahead with AGMA 6114 technical specs.

As far as I know, AGMA code specifically makes reference to AWS D1.1 (I do not have a copy of the standard).