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Computer models of steam pipeline components in the evaluation of their local strength

Okrajni J., Essler W.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 39, nr 1

71-78

EN

Purpose: The paper discusses the issue of modelling the heating and cooling processes of T-pipes in a power plant pipeline in the start-up conditions of a boiler. The main purpose of this work is the description of the mechanical behaviour of power plant components working under mechanical and thermal loading and validation of the computer modelling methods. Design/methodology/approach: The FEM modelling has been used to describe the local stress-strain behaviour of the chosen component. Findings: The reasons for the presence of high and variable in time temperature gradients in the components of the main steam pipeline include, among other things, variable values of the coefficient of heat transfer between the pipeline material and the medium flowing inside it, which, at this stage of boiler operation, may change its state. Unsteady operation of a pipeline, especially in case of subsequent boiler start-ups, may induce thermal stresses which exceed the values of allowable stress in components of complex shapes. Research limitations/implications: The possibility of applying the durability criteria currently assumed in standards still requires justification and confirmation in laboratory and industrial conditions to be closer to the real components behaviour. In such situation the presented analysis is the part of the complex investigation method which main purpose is increasing accuracy of the TMF process description and thermo-mechanical life assessment. Practical implications: The calculations carried out may constitute a basis for developing a material test parameters which would bring closer the fatigue conditions appearing locally in the analysed components. The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed. Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant component. This method includes the temperature fields analysis taking into account the boundary conditions based on the operation parameter data and the thermoplastic material model. The material stress-strain behaviour has been treated as the local phenomenon, that could be modelled by FEM.

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Małocykliczne zmęczenie cieplne konstrukcji rurowych

Król S., Essler W., Pietrzyk M.

Energetyka

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2003

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nr 10-11

681-683

PL

Przedstawiono mechanizm zmęczenia cieplnego niskocyklowego stali 16M. Stwierdzono, że cykliczne naprężenia cieplne, powstające przy zmianach temperatury w zakresie 20-400°C i jednoczesnym ograniczeniu swobody odkształceń cieplnych, powodują w elemencie konstrukcyjnym typu "opłetwiona rura" niszczenie w wyniku zmęczenia cieplno-mechanicznego. Dekohezja przebiega początkowo wg mechanizmów zmęczeniowych, dalej poprzez łączenie się mikroszczelin na drodze ścinania w osnowie metalicznej, a następnie jest uaktywniana procesami pełzaniowymi.

EN

The mechanism of small-cycle thermal fatigue of 16M steel is presented. It is stated that cyclical thermal tensions occurring during temperature changes within the range of 20-400°C, with simultaneous limitations on thermal deformations, cause damage resulting from thermal - mechanical fatigue in the "finned pipe" structures. De-cohesion is initially carried out according to the fatigue mechanisms, next it goes through the stage of micro slots combination, caused by shearing in the metallic matrix, and then it is activated by a creeping processes.

3

Zmęczenie cieplne stali o osnowie ferrytycznej w konstrukcjach rurowych

Król S., Pietrzyk M., Essler W.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

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z. 75

121-125