Monorail welds Cracking

[jayinwww]

I got called to look at a job where they did MT on existing stitch welds. The stitch welds are welding monorail to a structural I beam. The client asked the contractor to remove the weld then reweld new weld. I was surprised they didn't do any LPI to make sure of no cracks in parent material before welding new weld in it's place.

The new welds are starting to crack along the toe and into the parent material. Preheat was done at 200. No other heat treatment was used. I saw a PMI report and it came up as, Cr 0.67, Fe 96.8 & Mn 0.66.

My conclusion is they should have performed NDE prior to new weld being deposited. Would there be any other reason for the cracks? I'm not sure how old this is and Im not sure if monorails are special with regards to type of steal ductile or harded.

 

[WARose]

All sorts of reasons a weld can crack: residual stresses in the materials involved, hydrogen content, base material problems (including carbon content). It's hard to tie down to one thing based on the info provided. If you think they haven't done the proper testing of the metal involved, that might be a great place to start. Also I'd be curious how many times this area has seen welding.....you make it sound like twice....but if it is more that that, I'd start wondering about the residual stress theory. (Technically, I might start wondering after only twice depending on the properties of the base metal.)

If you don't mind me asking: why not bolt it to the beam you want to hang it off of?