Weld cracks joining A544 tube to A269 304

[laserfab]

We have an application where we join a 16ga 304 1.375 od socket elbow to 16 ga wall 1.375 od tube. Both start as seam welded product. They are both supposed to be A269 which has worked fine previously, this is a low pressure heat exchanger, fluid approx 250 deg fh.

Now we have encountered elbows which were A544 and have had resulting cracks in the a544 product. not at the welds but right next to the weld region. There is also some mechanical stress at the connection point.

Would anyone have some reasons why the A544 has such a poor mechanical result. Any ideas would be greatly appreciated.

Thanks

 

[metengr]

Are you sure about reference to A544? This is a carbon steel wire specification and it was withdrawn in 1989.

 

[laserfab]

Yes! I was typing way too late last night
ASTM-A554. Thank you.

 

[metengr]

The A 554 is for welded stainless steel mechanical tubing used in general applications. Are these new tubes or are you welding to existing tubes and suffering cracking? This was not clear to me.

The problem with A 554 tubing is that this material can be supplied in a cold worked condition with no nondestructive testing required. This is tubing for general purpose so you get what you pay for when ordering.

 

[laserfab]

The tubing is all new not related to repairs or refurbish

 

[metengr]

laserfab;
You may have a bad batch of mechanical tubing because you have cracks seen visually. Now my question is have you confirmed these as cracks or could they be surface imperfections? Was the A 554 tubing evaluated by an ASNT Level II examiner?

 

[laserfab]

I am in the process of analyzing the parts. The cracks were not apparent at time of weld and the unit passed its hydrostatic test, way beyond the operational level. However the failure occurred at the time of initial live testing. I currently have the parts at a lab waiting on chemical analysis and hardness testing. I was also going to use some Magnaflux spot check on the parts. I may look into a ASNT examiner, I was not familiar with this.

 

[EdStainless]

I see a few possibilities
1. High levels of cold work and residual stress, could lead to tearing of the parts when welded
2. What about chemistry? It is possible that the fitting has a chem that results in hot cracking.
3. defects from the forming could be giving way under the stress of weld solidification.

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