The Test of Inner-flue Tube Wall Temperature of Superheater Based on the Power Plant SIS
Superheater and reheater tube failures were mostly due to excessive temperature, the inner-flue tube wall temperature of superheater make certain of tube thermal stress, material creep status and residual lifespan of tubes. So investigation of superheater safety began with experimentation of inner-flue tube wall temperature of superheater. In order to precisely learn inner-flue tube wall temperature of superheater of 600MW supercritical boiler, new measuring points are set on the superheater tube wall inner the flue. Since the working condition of 600MW supercritical boiler is quite severe, the temperature measuring points can only be used for short-term test. The data acquisition can be carried out automatically and a data storage system is required. The testing method in this paper transmit the measuring signal to the database of the thermal power control system through the redundant channel of the system. This method only requires new measuring points (thermocouple). The test data can be loaded directly from the SIS database, which saves not only money but also the work.
Characterization and growth modeling of ash deposits in coal fired boilers
Abstract An ash deposit growing model based on surface growing theory is developed in order to represent the coal fired ash deposits. The predicted characteristics are compared to physical and chemical measurements of a typical ash deposit collected from an existing coal fired power plant located in the south of Brazil. Several structures were generated and compared to scanning electron images of ash deposits collected from the steam superheater section. The physical and chemical characteristics of the ash deposits, such as porosity, pore size distribution and fractal dimension of a typical ash deposit were measured using SEM image. All the images were analyzed using Imago software. Also, the existing ceramic phases were quantified using EDX detection and X-ray diffraction. The proposed random trajectory particle deposition model led to good agreement when compared to the macro quantities such as porosity and fractal dimension. It is expected that the modeled porous structure can be used for further heat transfer analysis and evaluation of coal-fired steam boiler designs.
Weld Repair of 2-1/4Cr-1Mo Service-Aged Header Welds
The objective of this investigation was to evaluate the efficacy of different weld repair techniques as applied to service-aged 2-1/4Cr-1Mo steel weldments. A header which had been in service for 244,000 h at 1,050 F (565 C) was utilized for the study. Three girth welds were partially excavated and subjected to repairs using gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW) with postweld heat treatment (PWHT), and without postweld heat treatment using a temperbead technique. Results show that all the weld repairs improved the creep rupture lives of the ex-service weldments and that remaining lives of several decades could be achieved in the repaired condition. The SMAW-temperbead repairs resulted in increase of future life, tensile strength, and impact toughness compared to the SMAW-PWHT repairs. The GTAW-PWHT repairs also produced a superior combination of mechanical properties. Remaining creep rupture lives were a function of the extrapolation procedure and specimen size. These results are described here and discussed in comparison with results previously reported for a less severely degraded condition of the steel in order to delineate the effect of prior degradation on weld repair performance.