The guy said he did it all the time, one of the few people that specializes in it on this side of the state.

It was scary as hell until we realized it was just as he said as we watched him heli-arc a 2 foot long crack in the tank. But then we still didn't come from behind the 1.5 foot thick reinforced concrete wall. If you know what I mean?

The thing is, the company couldn;t afford to have this truck out of service for long. We had put a crack patch on the tank, for a few weeks. The truck had gone through an inspection point, was flagged as "exempt from service" for the crack. Until it was fixed or replaced. Since the tank was a 2000 Gallon custom job, cost was very big to replace it and would be weeks before the replacement would come.

The weld was a 100% penetration weld (I don't know how he was able to keep it from melting through and leaking) and because of the diesel fuel cooling it, the weld was able to be ground down and polished to match the rest of the tank. You could only detect it if you really look, as the aluminum filler rod he used was a special oxygen free flux coated.

To this day, I WILL NOT WELD ON FULL FUEL TANKS. He said any fuel except Liquid Propane was doable. I can understand that.

[edit]
Oh yeah, this was when I was working as an "afternoon diesel mechanic/night truck fueler/saturday truck washer" for a logictics, storage and TL/LTL trucking firm here in Grand Rapids, called Van's Delivery.