Stress Analysis for Integrity Assessment of High-Energy Hot Reheat Pipe Bends of 210 MW Coal-Fired Unit

Abstract

The critical high-energy piping components of thermal power plant are predominantly subjected to damage mechanisms of creep , fatigue, and their interactions during their service. These pipings at high temperature and transient loadings under sustained loadings and thermal movements are designed as per the piping code . The creep damage mechanism causes irreversible thermal expansion in the piping inducing thermal stresses. The pipings under altered state of stresses due to thermal expansion are supported by suitable hangers and supports for ensuring stresses to be within the permissible design limits. The present paper discusses the layout of hot reheat piping of a coal-fired 210 MW_e unit. The piping material as per specification ASTM A335 P22 with hot reheat steam temperature 540 °C and hot reheat steam pressure of 4.7 MPa pressure operates under creep domain. The piping under these pressure and temperature loadings is subjected to load ramps during the start-ups, shutdowns, and load fluctuations and the steady loading during the sustained load operations. The scope of the study includes hot reheat pressure and low-pressure bypass pipelines. The piping layout with respect to the designed stresses, stress ratios, support loads, element forces, and displacements at each node has been considered for the present ongoing assessment. The design of the piping layout is accomplished to ensure that the structural integrity of the piping doesn’t exert excessive load to the nozzles of the connecting equipment. The stress analysis of the piping and support system should be carried out to ensure that the stresses are within the allowable values as per the applicable design code during the service. The stress analysis data were utilized in modeling the pipe bend before control valve of the intermediate pressure turbine for online creep fatigue damage monitoring.