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Design and Analysis

Thermomechanical Analysis of a Pressurized Pipe Under Plant Conditions

[+] Author and Article Information
T. P. Farragher

Mechanical and Biomedical Engineering
College of Engineering and Informatics
NUI Galway
Galway, Ireland

S. Scully

ESB Energy International
ESB Head Office
27 FitzWilliam St.
Dublin 2, Ireland

N. P. O'Dowd

Department of Mechanical
Aeronautical and Biomedical Engineering
Materials and Surface Science Institute
University of Limerick
Limerick, Ireland

S. B. Leen

Mechanical and Biomedical Engineering
College of Engineering and Informatics
NUI Galway
Galway, Ireland

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received June 20, 2011; final manuscript received April 29, 2012; published online December 5, 2012. Assoc. Editor: Allen C. Smith.

J. Pressure Vessel Technol 135(1), 011204 (Dec 05, 2012) (9 pages) Paper No: PVT-11-1140; doi: 10.1115/1.4007287 History: Received June 20, 2011; Revised April 29, 2012

This paper is concerned with the development of a methodology for thermomechanical analysis of high temperature, steam-pressurized P91 pipes in electrical power generation plant under realistic (measured) temperature and pressure cycles. In particular, these data encompass key thermal events, such as “load-following” temperature variations and sudden, significant fluctuations in steam temperatures associated with attemperation events and “trips” (sudden plant shut-down), likely to induce thermomechanical fatigue damage. An anisothermal elastic-plastic-creep material model for cyclic behavior of P91 is employed in the transient finite element (FE) model to predict the stress–strain-temperature cycles and the associated strain-rates. The results permit characterization of the behavior of pressurized P91 pipes for identification of the thermomechanical loading histories relevant to such components, for realistic, customized testing. This type of capability is relevant to design and analysis with respect to the evolving nature of power plant operating cycles, e.g., associated with more flexible operation of fossil fuel plant.

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References

Figures

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Fig. 5

Graphical representation of two-layer viscoplasticity model [15]

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Fig. 4

Dimensions and thermomechanical loading conditions of P91 pipe

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Fig. 3

Steam, pressure, and enclosure air temperature histories for “load-following cycle” (it is assumed that the enclosure air temperature is constant at 430 °C)

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Fig. 2

Steam, pressure, and enclosure air temperature histories for cold start cycle

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Fig. 1

Assumed steam, pressure, and enclosure air temperature histories for “simplified cycle”

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Fig. 8

Predicted inside and outside surface temperature history for simplified cycle

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Fig. 11

Predicted evolution of creep and plastic hoop strains for simplified cycle of Fig. 1

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Fig. 6

(a) Uniaxial hysteresis loops from two-layer viscoplasticity model (b) uniaxial hysteresis loops from two-layer viscoplasticity model compared against test data from Saad et al. [3], (c) uniaxial hysteresis loops from two-layer viscoplasticity model compared against test data from Saad et al. [3] and (d) Uniaxial hysteresis loops from two-layer viscoplasticity model compared against test data from Saad et al. [3]

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Fig. 7

Predicted effect of strain rate on isothermal uniaxial hysteresis loops

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Fig. 9

Predicted hoop stress–strain response at inner pipe surface for simplified cycle of Fig. 1

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Fig. 10

Predicted hoop stress response at the inner pipe surface for simplified cycle of Fig. 1

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Fig. 12

Predicted FE thermal histories for inside and outside pipe surface for N = 1, for cold start cycle of Fig. 2

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Fig. 13

Predicted hoop stress–strain response at inside surface of pipe at N = 1 for cold start cycle of Fig. 2

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Fig. 14

Predicted evolution of creep and plastic hoop strains for cold start cycle of Fig. 2

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Fig. 16

Predicted thermal histories at inside and outside surfaces of pipe for load-following cycle of Fig. 3. Inside surface temperature drops to almost 158 °C at the trip

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Fig. 17

Predicted hoop stress–strain response at inner pipe surface for trip part of load-following cycle of Fig. 3

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Fig. 18

Predicted sudden trip-induced transient hoop stress response in load-following cycle of Fig. 3

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Fig. 19

Predicted time history of creep and plastic hoop strains for trip-induced transients in load-following cycle of Fig. 3

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Fig. 15

Predicted hoop stress–strain response at inside surface of pipe for first four cycles for cold start cycle of Fig. 2

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