What was found
(CAN) PRESENCE OF FUEL WAS DETECTED IN APU FUEL FEED LINE SHROUD, BENEATH CABIN FLOOR BETWEEN FRAMES 46 & 79. AFTER REMOVING A SECTION OF SHROUD FROM DRAIN TO FRAME 46 & GOING AFT, FUEL SHROUD AFT OF FRAME 79 STOPPED SHOWING PRESENCE OF FUEL. APU FUEL FEED TUBE SECTION FROM FRAME 79 TO FRAME 84 WAS REMVD & PRESSURE LEAK CHECKED. A MICROSCOPIC LEAK SOURCE WAS CONFIRMED FROM FUEL FEED TUBE SUPPORT FLANGE WELD. WELD CRACK IS TOO SMALL TO BE SEEN VISUALLY. FUEL FEED TUBE WAS REPLACED PER AMM 49-31-21P.401. DAMAGED FUEL FEED TUBE FLANGE IS LOCATED ON SUPPORT BRACKET UNDER FLOOR, IN SERVICE COMPT AFT OF BULK CARGO, 40 IN FWD OF PRESSURE BULKHEAD.