Stress Cracks in fuel tanks

I was ask to fix another fuel tank its a square tank that is used to haul fuel in a pickup i think it is 100 gallons. Both had angle iron that some one had weld on to bolt it down and thats were they crack at the welds. I welded one earlyer this summer that had the same problem i havent ask how it was doing. I wonder if i am wasting my time and they will crack agin in the same spot?

Stress Cracks in fuel tanks