Re-Extension of 200 MW Turbine Cast Casing Service

To date, the fleet service life of a significant number of DTEK Energy power units is ex-ceeded. In particular, this relates to the structural components of the K-200-130-3 steam turbine of the power unit No. 9 of DTEK Luganskaya TPP. There is a need to make a decision on the admissibility of further exploitation. This requires a comprehensive study of the technological state of the base metal and the check calculation of its most critical high-temperature elements. A complex of such works was performed earlier in 2009. A special feature of re-extending the service life of this power unit is the super long fleet equipment operating time, presence of damages in the form of cracks and crack surfaces in the high- and intermediate-pressure cylinder casings, as well as the active involvement of equipment to operate in maneuverable modes when covering peaks of electrical load. This paper assesses the residual life of casings on the basis of three-dimensional models of the K-200-130-3 steam turbine high-pressure (HP) and intermediate- pressure (IP) cylinder casings. In doing so, the paper takes into account the actual operating conditions according to the damage data obtained from the results of inspecting the power equip-ment metal condition during preventive maintenance overhauls. The calculation of tem-perature fields is performed for typical operation modes, namely stationary operation at nominal power and starts from cold, warm, and hot states. The boundary value problem of heat conduction was solved using the finite element method of computational domain discretization. The calculation of the stress-strain state (SSS) was made taking into ac-count the effects of the main types of forces − temperature stresses, uneven temperature fields, forces from the steam atmosphere pressure, supporting forces. The maximum stress intensities for all the investigated modes of operation are observed in the toroidal parts of cylinder casings in the region of steam admission and correspond to the crack formation zones that were determined during the non-destructive testing of the metal. The assess-ment of long-term strength and low-cycle fatigue resistance showed that the residual life of the high-pressure cylinder (HPC) casing is satisfactory, and allows extending the op-eration by 100 thousand hours with standard safety factors. For the intermediate-pressure cylinder (IPC) casing, the residual life is 50 thousand hours with reduced safety factors.

Abstract licence: CC BY

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