(34c) Steam Turbine Internal Blade or Diaphragm Corrosion and Fatigue Failure

Mechanical drive steam turbines take the important role of main equipments in petrochemical plants.

These turbines are protected for safety reasons by monitoring and protection systems. However, in

some case, a turbine has the severe mechanical damage due to abnormal condition during long-term

operation or mis-application.

The failure damage modes of mechanical steam turbines are classified in terms of main components

as steam flow path parts, rotating such as rotor, groove, disk, blade and stationary parts such as control valve,

bearing.

This paper introduces the actual experience of turbine internal parts damage and the mechanism as

case study of failure / damage in terms of solid particle, water droplets erosion, thrust bearing heavy

rubbing, corrosion fatigue blade failure, diaphragm and blade and rotor disk failure.

On the contrary, for urgent plant recovery or to minimize the duration of no spare rotor, a damaged

turbine has to be repaired in as short schedule as possible. In order to repair the damaged turbine rotor in emergency as required by end users, the new welding techniques are developed based on risk analysis of repair and laboratory element tests.

The author introduces methodologies for repairing rotors by special welding procedures. These procedures consider welding condition and detail strength calculation to confirm the integrity, and heat transfer

analysis for proper heat treatment condition. These basic procedures are discussed in details.

Finally, the typical cases of the repaired rotor of large and high speed steam turbine are discussed.