Analysis of superheater tubes degradation at a tangentially fired pulverized coal power plant (original) (raw)
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A failure in any power plant will finally affects the shutdown of the plant and affects the Power supply by the plant that leads to the serious losses. The Failure of the power plant is mostly due to failure in the Boiler tubes of different zones such as Super heater and Re-heater tubes. Failure of tubes in boiler of the power plants may occur due to various reasons. These failure were mainly in the first row of the primary super heater tubes, therefore, these tubes are replace during the annual shutdown. As a tool for failure analysis, oxide scale thickness measurements were used to investigate the Remaining Life of tube. In this paper, the oxide scale thickness of these tubes were measured and used for analysis of remaining life of tube. The measurements also provide an illustration of the distribution of heat transfer of the primary super-heater tubes in the boiler system. For this analysis, were used pipes taken from the same power unit with different values of inner oxide layer...
Remaining Life Evaluation of Boiler Pipes Based on the Measurement of the Oxide Layer
2014
Boiler pipe failures are the most common cause of forced shutdown of power generation units. The oxide layer formed in the inner wall of those pipes is the main cause of overheating failures. From the measured value of the inner oxide layer, it is possible to estimate the remaining life of the component through correlation with parameters already established by the scientific community. Methodologies to estimate remaining life of components in power plants have been developed by Cepel, in accordance of global tendencies and the needs of Brazilian facilities. With the recent equipment acquisition for the detection of defects and measurement of thickness by ultrasonic, it became possible to measure both the pipeline wall and the internal oxide layer thicknesses. This paper presents a comparison between internal oxide layer thickness measurements of pipes performed by ultrasonic (non-destructive technique) and by metallographic preparation associated to optical microscopy (destructive ...
Critical Failure Analysis of Superheater Tubes of Coal-Based Boiler
This paper highlights a methodology for failure investigation of superheater tubes made of the material T-22 of a coal-based boiler. The process includes visual observation, the identification of sampling locations, the determination of the bulk chemical composition of the base alloy, microstructural investigation using optical microscopy, the exploration of finer structural details using a scanning electron microscope (SEM), the evaluation of hardness over samples obtained from different locations, the fractographic analysis of different failed locations, the X-ray diffraction (XRD) study of corrosion products adhered to inner surfaces, and the determination of the nature of the failure. Within a span of four months, three successive failures of superheater tubes were reported. The tubes were observed to have undergone significant wall thinning. Microscopic examinations using SEM on the failed region and a region some distance away on the as-received tubes were conducted in order to determine the failure mechanism. Layer-wise oxidation corrosion (exfoliation) in the inner surface was observed. Apart from major cracking, a number of nearly straight line crackings were observed in the longitudinal direction of both tubes. Close to cracking/bulging, void formation/de-cohesion of grain boundary indicated creep deformation under service exploitation. The failure mechanism was identified to be a result of excessive oxidation corrosion along the inside wall to reduce thickness, the spheroidization of alloy carbides and the coarsening of precipitate as well as creep void formation along grain boundary leading to inter-granular cracking with material flow near regions covered with thick scales. Moreover, there was a drastic reduction in bulk hardness of alloy and finally ‘thin lip fish mouth’ fractures. Keywords: coal based boiler, corrosion, creep, fractographic analysis, SEM, superheater tube Highlights • Bulk chemical composition of base alloy has been determined. • Optical microscopy has been applied for microstructural investigation. • Details of finer structural have been explored by applying scanning electron microscope (SEM). • Hardness of samples obtained from different locations of failed tubes has been evaluated. • Fractographic & X-ray diffraction XRD analysis has been performed at different failure locations. • Nature/type of failure to highlight the cause of failure ae has been examined.
Analysis of a Failed Primary Superheater Tube and Life Assessment in a Coal-Fired Powerplant
Journal of Failure Analysis and Prevention, 2015
The paper presents results of failure analysis of a primary superheater tube in a steam powerplant boiler. The boiler has been in service for around 52,000 h (6 years) and failure occurred on one of the primary superheater tubes in the form of a wide-open burst with appreciable wall thinning. The location of failure was first determined by on-site visual examination. Subsequently, specimens were taken from a region near the fracture surface for chemical analysis, microstructural examination using optical microscopy, and scanning electron microscopy equipped with energy-dispersive X-ray analysis to determine the probable cause of failure; whereas the lifetime of the superheater tubes was assessed using stress rupture test. Results suggest that the cause of failure was overheating due to deposit buildup inside the superheater tube which acted as thermal barrier and wall thinning resulted from direct impingement of flue gases. The lifetime of the superheater tubes is estimated and is discussed in the present investigation.
Role Of Oxide Scale Thickness Measurements In Boiler Conditions Assessment
2011
Oxide scale thickness measurements are used in assessing the life of different components operating at high temperature environment. Such measurements provide an approximation for the temperature inside components such as reheater and superheater tubes. A number of failures were encountered in one of the boilers in one of Kuwaiti power plants. These failure were mainly in the first row of the primary super heater tubes, therefore, the specialized engineer decide to replace them during the annual shutdown. As a tool for failure analysis, oxide scale thickness measurement were used to investigate the temperature distribution in these tubes. In this paper, the oxide scale thickness of these tubes were measured and used for analysis. The measurements provide an illustration of the distribution of heat transfer of the primary superheater tubes in the boiler system. Remarks and analysis about the design of the boiler are also provided.
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.
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.
Analysis of superheater tubes failure
E3S Web of Conferences, 2019
Failures of boiler pressure parts, which working in high temperature and pressure conditions are often caused by overheating or corrosion. These two parameters are decisive, but not the only ones. Local stress concentration also depends on the type of headers support and external loads from pipelines. Boiler pressure parts subjected to all loads mentioned before are steam superheaters. Thermal expansion, high pressure and temperature lead to shortening superheaters lifetime. In the places with significant stress caused by all load combinations it is difficult to predict creep strains and material structure changes. This paper shows superheater in which considering external loads from pipeline and their influence on the stress concentration in the superheater tubes. This article also shows steel S304H creep analysis for 100k [h] results and creep equation with experimental developed constants.
Analysis of Superheater Boiler Tubes Failed through Non-linear Heating
Procedia Engineering, 2014
The failure of two superheater tubes (T1&T2) is analyzed in the present investigation. The tubes are fractured perpendicular to tube length and bowed down towards the fire side without any brittleness, as examined through naked eye as well as tensile testing. There is no material loss from inside of tubes. Outer surface wall is thinned down by erosion and corrosion mechanism through fly ash deposits. Subsequently, the non-linear heating leads the catastrophic failure after short service period.
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.