Remember the leak from SARRY in February? TEPCO released the analysis of the pipe that leaked highly radioactive water from the Toshiba's cesium absorption system, and it sure looks like a bad weld, from the photos of inside the pipe.
It is particularly bad on the left side of the rust. The leak occurred BELOW the weld, but the bad weld may have contributed to the rust and corrosion of the pipe.
From TEPCO's Photos for Press, 3/12/2012 (click for bigger image):
Strangely, TEPCO does not blame the weld. The company blames sodium hypochlorite (bleach) which is injected in the water to "prevent the microbially caused clog" (from their document, page 3) to have caused corrosion.
If you're wondering "microbe??", it's because TEPCO mixes the treated water with the filtered river water and inject the water back into the reactor.