What was found
PHX - MAJOR REPAIR - DURING 8 DAY CHECK REPORTED CENTER KEEL BEAM PANEL BULGING WITH PULLED FASTENERS LOCATED AT STA 582, JUST RIGHT OF CENTER TANK SUMP ACCESS PANEL. MAINTENANCE BLENDED OUT CORROSION AT KEEL BEAM RT SIDE STA 576-582, BL 6.5R. INTERGRANULAR CORROSION ON LOWER KEEL BEAM VERTICAL LEG IS OUT OF SRM LIMITS IAW BOEING 737-300 SRM 53-60-12. REMOVED AND INSTALLED NEW SECTION OF KEEL BEAM FROM STA 520-625 IAW BOEING 737-300 SRM 53-60-12 FIG 203.