22065 SS Hollow Shaft Failure 1

[unclesyd]

This is mainly for your information,but I would appreciate any comments.

This is 2205 SS hollow shaft operating around 400°F that had a short happy life of 6 months.

This is a problem where one has 4 unknowns and 4 equations. The thermal history of the weldment is missing, along with the welding procedure used. There is no procedure for the use of a backing ring in fabricating this weldment.

There were some attempts by an unknown welder repair a previous leaks, which were unknown to operations(?).

The break is at the 1/3 mark from the driven end so it's in a bad place. The whole shaft only needed to be 2 sections.

I'm trying to get some better pictures.

Should have loads, mainly speed and input torque tomorrow.

The first picture is real interesting.

http://my.engineering.com/action/file/download?file_guid=427623

http://my.engineering.com/action/file/download?file_guid=427625

http://my.engineering.com/action/file/download?file_guid=427628

http://my.engineering.com/action/file/download?file_guid=427627

http://my.engineering.com/action/file/download?file_guid=427626

http://my.engineering.com/action/file/download?file_guid=427624

 

[metengr]

unclesyd;
Thanks for the information. An initial thought, the duplex 2205 is notorious for developing intermetallic compounds above 600 deg F. Based on the rather brittle-looking appearances of the fracture surfaces and existing cracks with what looks like a heat tint band, it would appear that the temperature during welding easily exceeded 500 deg F and resulted in extremely low toughness/ductility near the weld region.

 

[unclesyd]

This one of those failures where you will never know the true as there is CMA and a little in house politics by everyone. I also hope to get closer than through pictures. They have the tools, 3 SEMs and a Zeiss Metallograph and Stereo Macro Camera.
My first question to the operators did you hear a big bang. quot: "the shaft gave on indication before it failed" even though someone made a futile attempt to weld up some leaks. I
concur that it certainly appears to be a heat tint band around part of the shaft. My comment about that was who put the torch on the shaft and if no one did the welder was certainly running a super hot weld bead.
I have asked about the heating media, Therminol, due to fact that there is a possibility that the shaft could have seen 700°F due to the equipment is on the primary vapor system which operates at 700°F. At one time the equipment was on a secondary system that would only allow 500°F
Right now the origin appears to be a lack of fusion in the weld root. There are three short areas of LOF and LOP.
Another thing that is a little odd is how the crack progressed using the backing ring as a guide. I could see this if the shaft was horizontal but it's inclined at 30°. I assume that the backing ring acted as a severe tress riser and investigation will show multiple origins.

 

[EdStainless]

Can you give us some physical dimensions also please.
A high strength alloy with relatively low ductility (in the welds maybe very low). You should have good fatigue strength but you will also be notch sensitive.
Misalignment or out of balance would create large stresses in this high strength material.
My first suspicion is that LOF created stress concentration notches for initiation. Poor control of the welds with some embrittlement would only make this situation worse.

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Plymouth Tube

 

[unclesyd]

Was hoping for more information today, so far no joy.

 

[stanweld]

Just about everything that would contribute to failure of a welded rotating shaft was done; from the use of a backing strip to the burn-though weld repair made without a back purge to the high heat input as evidenced by the wide heat tint band to the lack of a stress relieving heat tratment. I should think that failure was inevitable