Of course even reputable manufacturers do detect errors in manufacture which sometimes affect entire batches of goods. We cannot rule out the possibility that your computer dealership is replacing one faulty Seagate drive with another faulty drive from a bad batch. It was only a few months ago that re-branded Pentium chips were uncovered in SA, and only a few weeks ago that fake Epson printing products were seized. But the most obvious reason for your hard drives to have failed is your husband's welding activity. Welding machines, even small domestic machines, draw vast amounts of electricity.
Electrical spikes occur most often when lightning strikes.
Surges from lightning are powerful enough to destroy even less sensitive equipment, such as TV sets, and sometimes merely switching off your PC is not enough.