Page 122 - MY STORY

The findings sort of went like this:

1. The steel fittings were a welded assembly of high
strength steel

2. The weld quality was poor, containing several
relatively large voids in the weld

3. The heat treatment after welding to bring the welded
assembly to full strength was faulty in that the furnace

atmosphere used for heat treatment was not well
controlled, and significant surface decarburization of the

weld and parent metal area was noted. It is well
established that the lowered strength caused by
decarburization will dramatically lower the fatigue life of
steel parts.

4. An undetected fatigue crack started at the decarburized

surface, propagating for at least a couple of inches, in
some cases propagating from void to void, as evidenced
by fatigue striations noted on the carefully cleaned

fracture surface using electron microscope fractography.

5. The catastrophic fracture occurred starting at the

fatigue crack termination at stresses far below the