An inspection apparatus (40) for in-situ leak testing of the bell seal (30) of a steam turbine (10). The apparatus includes a pair of inflatable bladders (48,52) for defining a sealed volume having the bell seal (30) as its only leakage path. The mass flow rate of pressurized air (70) at various pressures through the bell seal (30) is compared to the known flow rates through a similarly designed bell seal having various degrees of degradation. A camera (60) rotated by motor (62) between the bladders (48,52) provides an indication of the proper positioning of the inspection apparatus (40) and facilitates a visual inspection of the bell seal (30) and retaining nut (42). The inspection apparatus (40) may be inserted into an inlet to the turbine through a disassembled flow control valve without the need for any disassembly of the turbine.