How did the x-rays come out? If slag was there why didn't they grind it out and re-weld it!
... the metal would bend to its yield point like taffy before a weld would crack.
Same as in the petrochemical field. The pipe tears before the weld breaks.
The Navy has had a terrible decade with shipbuilding. Not enough oversight, as in the El Paso debacle. HUGE UNFIXABLE MISTAKES are welded in before they are found, when it is too late to fix them.