Expanding bell seal

In a steam turbine having a main inlet pipe which introduces steam to a nozzle chamber through the turbine casings and a bell seal assembly for sealing the inlet pipe relative to the casings and the nozzle chamber, the bell seal assembly including a bell seal disposed in the nozzle chamber, and a retaining nut sleeved by the bell seal and threadedly engaged in the inlet pipe, the improvement which comprises a ring carrier replacing the bell seal, a stack of inner and outer sealing rings loosely sleeved on the ring carrier, with a lowermost ring resting on a lower flange of the ring carrier and with an uppermost ring being disposed in close proximity to the lower end of the inlet pipe, the inner diameter of the inner rings being slightly larger than the outer diameter of the ring carrier and the outer diameter of the outer rings being slightly smaller than the inner diameter of the nozzle chamber, the inner rings being made from a high strength super alloy which resists oxidation having a lower coefficient of thermal expansion than the material of the ring carrier, and the outer rings being made from a high strength super alloy which resists oxidation having a higher coefficient of thermal expansion than the material of the nozzle chamber wherefore, as the temperature increases during turbine start up the ring carrier expands into contact with the inner rings forming a tight seal therebetween at operating temperature and the outer rings expand into contact with the nozzle chamber forming a tight seal therebetween at operating temperature.