Thermal load non-uniformity estimation for superheater tube bundle damage evaluation (original) (raw)
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International journal of engineering and technology, 2018
10 Computational Fluid Dynamics (CFD) technique has been used to predict the metal temperature of 11 reheaters (RH) tubes in a typical supercritical utility boiler operating at design condition. The zone from 12 Furnace Outlet Plane (FOP) till RH section in upper furnace of super critical boiler has been modelled. 13 CFD analyses are carried out using Conjugate Heat Transfer (CHT) method by capturing transfer of 14 heat through metal walls, from flue gas to steam flowing inside selected RH tubes. The metal 15 temperature of these selected RH tube is predicted. Four cases have been studied covering 16 RH tube 16 assemblies and the pattern of metal temperature distribution on selected RH tube walls is predicted. 17 Three dimensional surfaces of wall temperature verses tube length for each of the RH tubes in 16 18 assemblies have been plotted which will help the designer in identifying likely zones of RH tube rupture 19 at power plant sites. Commercial tools Gambit, Icem Cfd and Ansys Fluent have been used for carrying 20 out the CFD analyses and plotting tool Gnu Octave has been used to generate three dimensional surface 21 plots. 22
Failure investigation of secondary super-heater tubes in a power boiler
Engineering Failure Analysis, 2009
The super heater is heart of any boiler system main duty of which is to supply desired amount of steam regularly at rated temperature and pressure. Frequent tube failure in super heaters is found to be crucial problem which is directly related with boiler operation, performance and design parameters. Aim of this paper is to predict possible causes of super heater tube failure. It deals with the failure investigation of secondary super heater tube panel of SA213-T11 grade steel. The primary observations made with visual inspection and then metallurgical investigation has been carried out by microstructure analysis. The temperature distribution on the tube walls of the super heater is analyzed using computer aided engineering tools. From CFD results and metallurgical examination, localized overheating was seen in failed region of super heater tubes. High erosion areas were also seen from computational fluid dynamics. The uneven temperature distribution over the super heater tubes leads to localized overheating, chilling and development of excessive thermal stresses. This analysis is carried out using multiphysics environment which is very useful tool for analysis of many industrial systems like heat exchangers, chillers, cyclones etc.
Numerical investigation of superheater tube failure
Industrial superheaters in petrochemical plants possess leakages due to failure in many areas. This paper presents the results of investigations into identifying the failure causes. The investigations were carried out by simulating the heating process of a superheater. The simulation was carried out numerically using ANSYS mechanical commercial software. The simulation results indicated that the superheater tubes were subjected to direct radiation heat transfer as well as flame violence. The leakage spots were formed due to cracks in the material mainly at the joint points between the tubes and the header. It was also realized that the welding at the connection areas of the pipes and the header had weakened the material and formed low thermal resistance spots which could not stand the 510°C temperature and consequently, it had either melted or cracked.
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.
Thermal Analysis of Superheater Platen Tubesin Boilers
Superheaters are among the most important components of boilers and have major importance due to this operation in high temperatures and pressures. Turbines are sensitive to the fluctuation of superheaterstemperature;therefore even the slightest fluctuation in the outlet vapor temperature from the superheaters does damage the turbine axis and fins. Examining the potential damages of combustion in the boilers and components such as the superheaters can have a vital contribution to the progression of the productivity of boiler, turbine and the power plant altogether it solutions are to be fund to improve such systems. In this study, the focus is on the nearest tube set of superheaters to the combustion chamber.These types of tubes are exposed to a wide range ofcombustion flames such that the most heat transfer to them is radiation type.Here, the 320 MW boiler of Isfahan power plant (Iran), the combustion chamber, 16 burners and the platensuperheater tubes were remodeled by CFD technique. The fluid motion, the heat transfer and combustion processes are analyzed. The two-equation turbulence model of k-εis adopted to measure the eddy viscosity. The eddy dissipation model is used to calculate the combustion as well as the P-1 radiation model to quantify the radiation. The overheated zones of superheater tubes and the combustion chamber are identified in order toimprove this problem by applying the radiation thermal shields and knees with porous crust which are introduced as the new techniques.
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.
Thermal load deviation model for superheater and reheater of a utility boiler
Applied Thermal Engineering, 2000
The extreme steam temperature deviation experienced in the superheater and reheater of a utility boiler can seriously aect its economic and safe operation. This temperature deviation is one of the root causes of boiler tube failures (BTF), which causes about 40% of the forced power station outages. The steam temperature deviation is mainly due to the thermal load deviation in the lateral direction of the superheater and reheater. This variation is very dicult to measure in situ using direct experimental techniques. In this paper, we propose a thermal load model that is based on the power plant thermodynamic parameters, thermal deviation theory, and¯ow rate deviation theory. It is found that the calculated results from our model agree well with the in situ experimental results. The predicted BTF positions are the same as that in the reheater of a 300 MW utility boiler at Wujing Power Plant. The proposed model has been used to improve the design of utility boiler in Boiler Works, predict the possible BTF in the design stage, and assess the existing designs. This model can also be applied to utility boilers of dierent manufactures, and has been successfully applied to the BTF prediction and prevention in the Power Station. #
Failure analysis and retrofitting of superheater tubes in utility boiler
The extreme spray water mass flow rate deviation was observed to occur in the middle temperature superheater of Sahand 2 Â 325 MW Power Plant utility boiler, which severely affected its economic performance and safe operation. Boilers operating in these conditions led to failure in superheater tubes at the same place for two consecutive times in a three year span. Thus, the failure analysis of superheater tubes by investigating the visual inspection, chemical, scale and creep analysis was carried out. The brittle failure occurred in the superheater tubes after the fuel was changed from natural gas to heavy oil. Failure analysis showed that tubes were suffering from long term overheating which was instigated by high spray water flow rate. In order to rectify the boiler operating conditions, some modifications were applied in the boiler unit 1 and operating parameters on this boiler were compared with boiler unit 2. The results showed that the 8.33% reduction in heating surface area corresponds to 52.84 and 17.80% reduction in spray water mass flow rate for capacities equal to 300 and 260 MW, respectively.
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.
Root-cause analysis of superheater-tube failure
Materiali in tehnologije
Superheater-tube failure is listed among the major causes of a fossil-fuel-fired boiler outage. Therefore, it is necessary not only to identify and repair it in the case of failure but also to eliminate the root cause of this problem. As there may be multiple reasons of failure in exposed equipment such as a superheater, a thorough investigation of more than one probable cause is usually required. This article focuses on a failure analysis of a boiler located in a chemical plant. After a leak was discovered, several cracks on the superheater tubes were identified as its main cause. It was necessary to assess the extent of the damage, detect the root cause and propose corrective actions. Two problematic locations with cracks were identified during the visual inspection: the first was on the superheater-tube bends and the other was the weld joint between the superheater and the transition pipe. As the first step, the material-microstructure and composition analyses of the tubes in these critical locations were carried out. Even though small weaknesses were found in the microstructure, the main cause of the tube failure was not identified. As the next probable cause, thermal-dilatation stresses were investigated using the finite-element analysis (angl. FEA). The support system, consisting of fixed and spring supports, as well as the compensator were included in the analysis that confirmed the thermal-dilatation stresses as the major cause of the failure. Based on the results, a new technical solution for the supports was suggested and verified with the FEA.