An Analysis of Creep Phenomena in the Power Boiler Superheaters (original) (raw)
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A Comparative Creep and Creep Fatigue Analysis of an Austenitic Steam Superheater
ASME 2014 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries, 2014
A steam superheater is a component which operates at elevated temperature in the creep regime. The component is normally not working in cycling conditions. Due to operation failures, the component has been subjected to several unplanned start-ups and shutdown. The SSH has reported a very high level of damage of the tubesheet to shell junction in field (high deformation and weld cracks). Several investigations have been performed to analyze the effect of temperature, pressure and external loads on the equipment with finite element techniques and different creep and creep-fatigue evaluation approaches: ASME III subsection NH, simplified inelastic analysis and a full creep model have been used. A comparison of the results is reported in this paper. Paper published with permission.
Modelling Creep Behaviour of Superheater Materials
Energy Procedia, 2016
The energy demand of human being is ever increasing. The naturally available energy resources are in a crude form and need conversion to one which is readily available for end use. Power plants play the role of this conversion process. Majority of the conversion processes take place at severe conditions of very high temperature and high pressure. Hence, power plant components always exhibit inelastic behaviours like creep and fatigue. The design of such components should take these inelastic behaviours in to consideration. This work focuses on modelling the creep behaviour of superheater materials. Specifically, creep constitutive model of T91 steel which is commonly used for constructing superheater tubes is developed and validated with results from experimental work. Then a material user subroutine has been written to incorporate the model in commercial software ABAQUS.
High Temperature Materials and Processes, 2008
The elastic, inelastic deformation and stress distribution pattern of a seventeen years service exposed primary superheater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500°C at various stress levels (40-177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service exposed tubes compared to the virgin material. Creep deformation behavior of the service exposed and virgin tubes of the same material at 40 MPa reveal that deterioration of the creep properties fall within the 20% scatter band, which is well within the specified limits of ASTM standard. The service exposed primary superheater tube is thus in a good state of health.
Simplified approach for creep evaluation in superheaters
IOP Conference Series: Materials Science and Engineering, 2020
This paper is focused on the estimation of temperature distribution on superheater tube bundles for the consequent creep damage evaluation. The precision of estimated temperatures is very important because it significantly affects residual creep life. Conditions in the tube bundle can be simulated using CFD, however, a full 3D simulation would be computationally intensive and not fit for practical use. In order to mitigate this issue, the new approach considered in this paper uses a series of 2D CFD simulations in multiple sections using known inlet flow conditions. Those conditions have been investigated in previous work using 3D CFD simulation of flue gas flow starting in the combustion chamber and ending just before the superheater in the second pass. The paper also deals with possible temperature differences that may arise due to simplifications in the proposed approach. Lastly, the residual creep life is estimated using obtained temperature distribution on the tube bundle.
Proceedings of the Asian Pacific Conference on Fracture and Strength and International Conference on Advanced Technology in Experimental Mechanics
A small punch creep testing technique using miniaturized specimen with a dimension of 1O ×.1O× O.3i mm has been demonstrated fbr evaluating change in creep property ofhigh temperature components due to long-term service operation, This technique was applied to SUS 316 HTB secondary superheater boiler tube actually used for 100,600 h in a fbssil power plant. The overall shapes of the creep curves deterrnined by the small punch creep test were similar to those obtained from a conventional uniaxial creep test. That is, they exhibited clearly three creep stages, The extent ofsecondary creep stage and rupture time t, decreased with a increase oftesting load level. The creep rupture life ofthe service-exposed tube was shorter than that ofthe unexposed tube atatemperature of650 ℃ and at high load leve]s, i.e. 338 N and 408 N, However, te the contrary, the former became longer than the latter at relatively low load levels, i.e. 234 N and 2g6 N, The difference in rupture life between them had a tendency to increase with a decrease of testing load level. These small punch creep behaviors ofSUS 316 HTB superheater boi]er tubes have been examined from ametallographicpointofview. Kby Pt2)rds : Small punch creep test, Creep, Material deterioration, Long-term service operation, Fossil boiler, Superheater tube, SUS 316 HTB
Mechanical thermal stresses and creep analysis of boiler tubes
2016
The boiler tubes are operated continuously at high temperature and pressure. Hence at high pressure for forces acting on the boiler tubes will be high. This research paper focuses on the analysis of one of the long term effect of continued application of high pressure on boiler tubes which causes creeping. By utilizing finite element modelling software, AUTODESK INVENTOR the effect of pressure with the increase in temperature distribution across the steam generator tube was evaluated. The increase of heat transfer rate across the wall caused the oxide scale thickness to grow more rapidly than normal condition. The thermal conductivity in the boiler tubes, life of boiler tubes and creep damage is also analyzed in this research paper. The AUTODESK INVENTOR result is analyzed to determine the main and interactive effects of operating conditions. The effect of steam on boilers and creep damage in comparison with temperature were researched. Optimum condition identification in order to m...
Influence of steam-side oxide scales on the creep life of a boiler superheater tube
Materiali in Tehnologije, 2018
Creep life is a limiting factor in the case of boiler tubes operating above the creep temperature and, for a given material, it is generally determined by the actual operating temperature and stress. Standard approaches to the calculation of a tube creep life mainly take into account the stress caused by pressure loading and the mean temperature in the tube wall. However, the estimation of the temperature and stress may be difficult for water-tube boilers because oxide scales tend to form on the inner surfaces of the tubes, exposed to steam and indirectly affecting the resulting creep life. As the scales increase the thermal resistance of a tube wall and, consequently, the wall temperature, the creep life is reduced. Moreover, the presence of oxide scales leads to a higher hydraulic resistance of a tube, which can cause further increase in the temperature in some tubes of the bundle if the oxide-scale growth rate is not uniform. Additionally, the elements increasing the creep streng...
SP creep properties of Gr.91 boiler pipings service-exposed in different USC power plants
Ubiquity Proceedings, 2018
The small punch (SP) testing technique was applied to five heats of Gr.91 steel, which had been actually used for boiler pipings in different USC power plants for long periods of time to investigate the applicability of this technique to the assessment of heat-to-heat variation of creep property. The experimental results revealed that the SP creep rupture strength and deformation behavior were quite different depending on the heat. Those differences in SP creep property, which could not be evaluated by hardness measurement, were qualitatively similar to those in standard uniaxial creep one. It was expected that the SP creep testing technique was applicable to the assessment of heat-to-heat variation for in-service boiler pipings.
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.
Metallurgical evaluation of creep-failed superheater tubes
Engineering Failure Analysis, 2009
The present study is focused on the metallurgical factors induced during high-temperature operation of a pipeline that resulted in its short-time failure. The pipeline is used as superheater in a lignite power-plant unit and is constructed by an array of steel tubes jointed together by circumferential weldments. Systematic recording of data over one year of service indicated that local material's failures were occurring, on an average, every 15 days and localised either at curved areas of the tubes, or in the neighbourhood of circumferential weldments. Visual inspection, macrographic examination and microscopic observations of representative failed parts revealed microstructural features indicative of creep rupture. In both cases, the material failed due to the rapid growth and coalescence of creep voids, initiated at a service temperature equal to 43% of the steel melting point.