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Research Papers: Operations, Applications & Components

Influence of a Variable in Time Heat Transfer Coefficient on Stresses in Model of Power Plant Components

[+] Author and Article Information
Jerzy Okrajni

Silesian University of Technology,
ul. Krasińskiego 8,
Katowice 40-019, Poland
e-mail: jerzy.okrajni@polsl.pl

Mariusz Twardawa

RAFAKO S.A.
ul. Łąkowa 33,
Racibórz 47-400, Poland
e-mail: mariusz.twardawa@rafako.com.pl

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 8, 2013; final manuscript received January 30, 2014; published online April 15, 2014. Assoc. Editor: Haofeng Chen.

J. Pressure Vessel Technol 136(4), 041602 (Apr 15, 2014) (6 pages) Paper No: PVT-13-1133; doi: 10.1115/1.4026799 History: Received August 08, 2013; Revised January 30, 2014

The paper discusses the issue of the modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behavior of power plant components operating under mechanical and thermal loading. The finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time. Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, that may change its condition, flowing inside them. For this reason, an evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology that combines computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behavior of components in question have been discussed.

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References

BS 7910, 1994, Guide on Methods for Assessing the Acceptability of Flows in Structures (replacing PD 6493 and PD 6539), British Standards Institution, London.
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Figures

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Fig. 1

Model of the main steam pipeline Y-junction

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Fig. 2

Steam temperature fluctuations close to the boiler as functions of time; (a) hot starting, (b) cold starting (cold start-up—the steam temperature at the beginning of process is lower than 200 °C)

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Fig. 3

Temperature versus time diagrams for the shallow point; experimental data and computational results for heat transfer coefficient of 1000 W/m2 °C; (a) hot starting, (b) cold starting

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Fig. 4

Diagram of changes of the heat transfer coefficient with time; (a) hot starting, (b) cold starting

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Fig. 5

Temperature versus time diagrams for the model and experimental results; characteristics determined for the selected point—located shallow under the outer surface (a) hot starting, (b) cold starting

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Fig. 6

Temperature versus time diagrams for the model and experimental results; characteristics determined for the selected point—located deep under the outer surface (a) hot starting, (b) cold starting

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Fig. 7

Difference of the temperature of points located “deep” and “shallow” fluctuations as functions of time; operation conditions—measurements and FEM model

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Fig. 8

Cyclic stress–strain curves of P91 steel as results of isothermal tests at temperature: 200 °C, 500 °C, 620 °C

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Fig. 9

Steam pressure fluctuations close to the boiler as functions of time

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Fig. 10

Locations of the point at which the stresses with time have been determined

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Fig. 11

Von-Mises stress changes with time at a selected point C (see Fig. 10) of the Y-junction surface for different types of loading

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Fig. 12

σzz stress changes with time at a selected points—O and In (see Fig. 10) of the Y-junction surfaces for mechanical and thermal loading

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