Residual Life Estimation of Service Exposed Reheater Tubes in a Boiler of a Thermal Power Plant (original) (raw)
Related papers
2011
This paper presents the high temperature tensile and the stress rupture properties of 150,000 hours serviceexposed superheater and reheater tubes made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours-100000 hours rupture strength as obtained from experimental data in the temperature range of 793 to 853K exhibit a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed superheater and reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level 40 MPa / 813K, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 813K.
Remnant Life Assessment of High Temperature Tubes in 250MW Boiler
Advances in transdisciplinary engineering, 2022
The fluctuation in temperature and pressure in boiler parts subjected to creep and fatigue stress and also fuel burnt and steam generation leads to corrosion in various areas in the boiler. Residual stress during manufacturing, the vibration due to flow over the tube, mechanical vibrations, erosion due to the abrasive nature of the fuel, does occur in boilers. All of the above, individually or combined lead to material degradation of different magnitude and will lead to failure. It also leads to reduction of creep life of superheater tubes and results in the necessity of superheater repair every 4-5 years with replacement of up to 30-50% of tubes. The remnant life assessment (RLA) of boilers predicts accurately the remaining life of high temperature tubes allows reducing the amount and cost of repair. The method of assessment of remaining life for superheater and reheater steel tubes operating in conditions of intensive high-temperature corrosion is presented in this paper. The method is based on measurements of tube wall thickness and corrosion resistance of particular steel.
FAILURE ANALYSIS OF BOILER TUBES OF A THERMAL POWER PLANT
A major portion of the total electricity generated in our country is through thermal power plants using direct combustion of pulverized coal. The majority of forced outages of these thermal power stations are due to premature failure of vital components such as boiler tubes. Case studies pertaining to the failure analysis of various kinds of boiler tubes such as super heater tubes, reheater tubes, and water wall tubes that have failed involving creep deformation and damage have been studied. In the present study the metallurgical investigations revealed microstructural degradations through the formation of creep voids at the grain boundaries and intercrystalline cracks due to continued exposure to higher temperatures. The microstructure of the lip portion of the burst has been found to change depending upon the temperature of the rupture. Rupture taking place between Ac and Ac 3 has revealed a mixed structure consisting of bainite due to the quenching effects of the steel. Similarly rupture taking place below temperature Ac 1 have been marked by divorced /degenerated pearlite and or spheroidised carbides in the ferrite matrix. Analysis made regarding the overheating (creep) failure of pendant reheater tubes indicates that surrounding temperature of the tube exceed several degrees higher than the components are designed for and also due to factors like erosion of tube surface by Fly ash, short supply of water through the boiler tubes caused by internal deposits.
Materials Science and Engineering: A, 2007
Superheater and reheater 2.25Cr-1Mo steel boiler tubes from a thermal power plant after 17 year of service at nominally 540 • C and 40 MPa were studied to predict their remnant life. The investigation included dimensional, hardness and tensile measurements in addition to accelerated stress rupture tests between 625 and 700 • C and microstructural examination. The microstructure of the service-exposed alloy was free from any signs of deterioration, and the hardness was within the expected ranges; however, tensile testing revealed an apparent loss of strength from room temperature to 600 • C. Accelerated rupture testing, on the other hand, did not reveal any degradation of rupture behaviour compared to that of the virgin alloy. Analysis of the stress rupture data predicted that the 17 years exposed superheater and reheater tubes could remain in continued service for at least 12 more years at the current stress-temperature conditions.
Failure Probability and Remaining Life Assessment of Reheater Tubes
International Journal of Engineering, 2013
In this study, a real and significant industrial problem in a steam power plant was investigated. Reheater tubes in boilers are under creep and the fireside corrosion mechanism that cause some of them to fail. Since the estimation of probability of failure (PoF) and remaining life (RL) is expensive and time consuming by the deterministic methods, in this work they were evaluated using structural reliability analysis and distribution analysis based on in-site tests and selecting an appropriate limit state function (LSF). The criterion used for this purpose is based on the creep lifetime model and uncertainties. Sensitivity analysis was also carried out in this research. The considered relationship among three affecting parameters on boiler tube failure including time, creep and fireside corrosion leads to evaluating RL besides PoF as well as obtaining PoF and RL simultaneously by selecting an appropriate time-based LSF. Most accurate results were achieved based on obtained PoF and RL values which cause to provide more reliable results for economic planning of future inspection periods. This leads to significant cost savings and operational safety improvements. A new software package, named RALA was developed via programming in Matlab. The obtained results are in good agreement with all data gained from the practical experiments in the power plant based on the previous studies.
Remaining Life Assessment of Superheater Tube in Boiler of Coal Fired Power Plant
MATEC Web of Conferences
The effect of strain range and temperature on the low-cycle fatigue behaviour and microstructure change during cyclic deformation of Alloy 617 for use in very high temperature gas-cooled reactor components were studied at elevated temperature starting from ambient condition. Increasing the strain range and the temperature was noticed to reduce the fatigue resistance of nickel-based Alloy 617 due to facilitating the transformation behavior of the carbides in the grain interior, precipitates along the grain boundary, and oxidation behavior inducing surface connected precipitates cracking. Initial hardening behavior was observed at room temperature condition during cyclic due to the pileup dislocation of micro-precipitates. The grain size was also taking a role due to the formation of an obstacle in the matrix. In the high temperature regime, the alloy 617 was found to soften for its entire life due to the fast recovery deformation, proved by its higher plasticity compared with lower temperature. The deformation behavior also showing high environmentally assisted damage. Oxidation behavior was found to become the primary crack initiation, resulting in early intergranular surface cracking.
Failure analysis of boiler cold and hot reheater tubes
Engineering Failure Analysis, 2007
An analysis was made on the failure and shut down of boiler cold and hot reheater tubes by chemical analysis of sediments, metallographic examinations, XRD, SEM and EDX studies. The mode of operation, maintenance, and feed water chemistry were also checked. It is concluded that the bad maintenance and feed water chemistry are the main causes of the failure, leading to various types of corrosion mechanisms, which are identified and discussed in this study.
Effects of Long-Time Service on the Material of a Steam Boiler Fire Tube
Materials Characterization, 1998
After 23 years of operation, the fire tube of a 2000 kg steam/h boiler broke down in a waterfilling operation. Because of the intense vaporization processes, the boiler body blew up at about 250 m. The study of metallographic features, of mechanical properties in various areas of the fire tube pointed out microstructural transformations that caused the material's embrittlement and damage.
Failure case studies of SA213-T22 steel tubes of boiler through computer simulations
Journal of Loss Prevention in the Process Industries, 2010
Increased temperature and decreased hardness values of the tube metal and development of oxide scale on the inner surface of boiler tubes over prolonged period of time are typical problems in power plants. Appropriate life assessments or condition monitoring of boiler tube should be carried out from time to time. Computer simulations may economically support the post-failure assessment method, i.e. visual inspections, metallurgical examinations and mechanical strength measurements. However, estimations obtained from the simulations may provide an advanced warning to take preventive actions prior to failure. In this work two failure cases of the reheater and superheater tubes made of a typical material of SA213-T22 steel are evaluated. As the oxide scales are increasingly developed on the inner surface, the increasing of temperature and decreasing of hardness value in tube metal for both cases are determined. The remnant life estimations are then made in the form of creep cumulative damages.
Residual life prediction of service exposed main steam pipe of boilers in a thermal power plant
Engineering Failure Analysis, 2000
This paper deals with residual life prediction methodology for more than 12.5 years service exposed main steam pipes of various boilers in a thermal power plant. Health assessment was made using destructive accelerated stress rupture and tensile tests at dierent temperatures, and some nondestructive tests. There was no evidence of localised damage in the form of surface cracks, cavitation or dents in the service exposed main steam pipes of all the boilers. So far as the remaining life at 5508C is concerned, it is possible to obtain a life of greater than 100,000 h at the hoop stress level of the service exposed pipes, provided no localised damage in the form of cracks or dents have been developed. It is recommended that a health check may be carried out after 50,000 h of service exposure at 5508C. 7