Thermal expansion normalization for large steam turbines in service

Some large steam turbines, especially older those, encounter some problems with their thermal expansion. This shows itself in the broken (leap-like) movement of the bearing pedestals while the turbine is being heated or cooled in the course of transients. This also results in distortion of the casings, torsion of the foundation frame crossbars, increased vibration, damage of the bearings and couplings, etc. The thermal expansion freedom problems hamper the turbine's start-ups since the relative rotor expansions attain their limits. The main causes why the turbine loses the thermal expansion freedom are the increased friction on the sliding surfaces between the bearing pedestals and foundation frame, increased transversal load on the turbine from the steam-lines connected to the cylinders, poor transition of the axial thrust between the cylinders, and insufficient rigidity of the foundation crossbars. Under consideration are a set of diagnostic, design, and technological measures to reveal the specific causes of the problems and to eliminate them. Among the most widespread and effective countermeasures are the placing of special fluoroplastometallic bands under the bearing pedestals and electrochemical facing of the keys' surfaces, adjustment of the support-and-suspension system and tightening of the foundation frame.