Appropriate Filler Material for a Weld Reinforcement

[CRG]

Hello,

I have a Republic RC-3 that had a failure of a highly stressed welded fitting on the landing gear. Republic stopped manufacturing the model in 1947 and they no longer offer any support for the model. In 1961 Republic issued a Service Letter giving inspection instructions along with the following repair information:

A recommended repair is to grind off all existing weld down to parent metal and arc weld with nickel steel rod, building up bead around the fitting.

There is not an A.D. associated with this problem and the fitting is not easily removed for inspection. The part that failed is a small 1/4 inch steel bracket welded to a larger steel fitting.

Question:
1. What is the best approach to select the appropriate filler material to repair the connection?
2. Should I get the material analyzed to determine the most suitable filler material?
3. Should I contact folks who regularly work on this model and blindly accept their recommendation if it seems reasonable?
4. Should I locate a used replacement? If I did this, I still would not know if this fitting might be subject to failure due to an inferior weldment. The problem starts with cracking so I could have the part tested prior to installation

Note: I am a Mechanical Engineer and as such, I do not know all of the FAA resources that might help me made a determination as to how to proceed. A licensed aircraft mechanic is doing the work on the aircraft for me; however, he is unfamiliar with the model. His preference is to locate a used replacement for this part. Because of the known manufacter’s defect, I am reluctant to install a used replacement without first being assured that the part was reworked properly.

Any comments would be appreciated.
CRG

 

[FieldTeam]

Listen to your Mechanic! You state that you had a failure. Was it a complete failure or did your mechanic find cracks during inspection? If the clevis cracked off the torque tube, your best bet is to buy a new/used/reconditioned landing gear torque tube assembly and have it inspected at an NDI lab for cracks or other damage. Then inspect this fitting at regular intervals as instructed in the service letter and repair if cracks are found to develop thereafter. It will probably cost you just as much to get what you have repaired. Service letter #58 sounds like a "bigger the blob, the better the job" fix for this. Could be that if you choose to weld your existing part, additional reinforcement might be needed. Good luck.

 

[CRG]

FieldTeam, thank you for the advice.

It was a complete failure of the attachment. No cracks were ever detected in the weldment before failure. The 1961 service letter recommended an examination with a 20X magnifying glass. It is not possible to inspect the torque tube in place with any confidence using any NDT method, even using a 20X magnifying glass as the manufactures service letter stated. The toque tube is buried in the hull of the seaplane. I could have the piece pulled every year for MT inspection; however, I am not convinced that this is the best resolution of the problem. Keep in mind that parts are very scarce for this airplane which had a limited production during the two years it was manufactured 1946 and 1947.

The 1961 Service News letter stated that there had been a number of failures of this fitting. It is highly unlikely that I can find a new part; however, I am looking, and I know of most of the resources for new and used parts for the RC-3. I am surprised that there is no AD calling for annual removal and NDT of this part. The problem is the fillet weld that the factory used, and all the inspection in the world will not solve the problem. With luck, inspection will catch the problem before complete failure. It did not this time. If repaired per the Service News letter, a full penetration weld can be specified with the additional fillet build up to the same factory weld size. This will reduce the shear loading of the weldment and should provide a permanent fix for the problem.

The final decision for the repair that is made will be with my mechanic and will follow all regulatory requirements. I was a bit disappointed with the loosely specified filler material “nickel steel rod,” as stated in the Service News letter. I would have been more comfortable with a detailed welding procedure listing acceptable filler materials. Any additional comments will be appreciated.


Thanks Again
CRG

 

[FieldTeam]

It would be nice if you had the Electrol Inc., Drawing A5110. You might be able to ask them if they still have this drawing on file, although I would be surprised if they did.

http://www.electrol.com

 

1. What is the best approach to select the appropriate filler material to repair the connection?

What is your base material?

http://www.lincolnelectric.com

ER80S-D2 is reccomended for 4130 structures.


2. Should I get the material analyzed to determine the most suitable filler material?

What does this part look like?
Building a new part my be a better option.

3. Should I contact folks who regularly work on this model and blindly accept their recommendation if it seems reasonable?

Probably.

4. Should I locate a used replacement? If I did this, I still would not know if this fitting might be subject to failure due to an inferior weldment. The problem starts with cracking so I could have the part tested prior to installation.

Your used replacement is going to be 60 years old already. Why isn't it in another plane already?

Tim

 

[WKTaylor]

behindpropeller...

Some welded parts were just destined to fail due to poor materials consideration during design. I suspect that several factors are at play in this failure...

Is this a large part? if not then suggest reverse engineering a replacement part with significant materials and design considerations. This way You can control [improve] the alloy(s), welding processes, Heat treating and tempering, machining, stress relief, configuration (stress concentrations), NDI, shot-peening, etc.

If this a large/critical part You may want to consult a professional engineer and/or metallurgist for a full evaluation... there maybe subtle factors involved.... and these folks may provide valuable insight into redesign [materials/processes and/or configuration]... and then help get the parts made PER SPEC.

Regards, Wil Taylor