Thermo-Mechanical Fatigue of Thick-Walled Components of Power Devices

2014 ◽  
Vol 224 ◽  
pp. 87-92
Author(s):  
Jerzy Okrajni ◽  
Mariusz Twardawa
Keyword(s):  
Thermal Loading ◽  
Thermal Stresses ◽  
Pressure Vessels ◽  
Operating Conditions ◽  
Power Devices ◽  
Stress Strain ◽  
Mechanical Fatigue ◽  
Transient Thermal ◽  
Temperature Strain ◽  
Plant Components

The main purpose of this work is to determine the mechanical behaviour of power plant components operating under mechanical and thermal loading. Computer FEM modelling of temperature strain and stress fields along with temperature measurements have been applied as the methods of research. The stress-strain diagrams for the selected points of plant components have been determined. It is readily apparent from the stress-strain characteristics that under unsteady operating conditions, components analysed in this paper, especially in the case of boiler restarts, may operate with transient thermal stresses which sometimes reach values higher than the yield point. Consequently, a thermo-mechanical fatigue process takes place in the materials of the components in question. This paper seeks to justify the necessity of the application of design methods which take into consideration the influence of TMF processes on the durability of highly reliable pressure vessels.

scholarly journals A Better Way to Support Horizontal Pressure Vessels Subject to Thermal Loading

1997 ◽  
Author(s):  
Alwyn S. Tooth ◽  
John S. T. Cheung ◽  
Heong W. Ng ◽  
Lin S. Ong ◽  
Chithranjan Nadarajah
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Pressure Vessel ◽  
Thermal Loading ◽  
Thermal Stresses ◽  
Pressure Vessels ◽  
Sliding Surface ◽  
Current Design ◽  
Horizontal Pressure ◽  
Regular Site

When storing liquids at high temperature, in horizontal vessels, the current design methods aim to minimise the thermal stresses by introducing a sliding surface at the base of one of the twin saddle supports. However, regular site maintenance is required to ensure that adequate sliding is achieved This may be difficult and costly to carry out. The aim of the present work, therefore, is to dispense with the sliding support and to provide saddle designs which although fixed to the platform, or foundation, do not result in the storage/pressure vessel being over-stressed when thermal loading occurs. The paper provides general recommendations for the most appropriate saddle geometries, and details the way in which ‘Design by Analysis’ and ‘Fatigue Life Assessments’ may be carried out using the stresses which arise from these designs.

Analysis of a Tubesheet Undergoing Rapid Transient Thermal Loading

2000 ◽  
Vol 122 (4) ◽  
pp. 476-481 ◽  
Author(s):  
W. Reinhardt ◽  
R. Kizhatil ◽  
G. H. McClellan
Keyword(s):  
Thermal Loading ◽  
Thermal Stresses ◽  
Yield Criterion ◽  
Thermal Gradients ◽  
Plasticity Model ◽  
Solid Plate ◽  
Shakedown Limit ◽  
Transient Thermal ◽  
Hill's Yield Criterion ◽  
Very High

Some Class I CANDU heat exchanger tubesheets experience very high in-plane thermal gradients under Level A/B transients. If the thermal stresses exceed the ratcheting limit of the ASME Boiler and Pressure Vessel Code, shakedown has to be demonstrated by an elastic-plastic analysis. The choice of the plasticity model and its parameters must ensure that shakedown is predicted only if it occurs in reality. Differences to uniaxial modeling are discussed, and a conservative way of predicting shakedown is presented. The perforated region of the tubesheet is replaced by an equivalent solid plate with anisotropic yield properties (Hill’s yield criterion). A lower-bound shakedown limit for this material is derived. An example analysis is presented that has been performed using a commercial finite element code. [S0094-9930(00)00303-6]

Transient Thermal Stresses in Slabs and Circular Pressure Vessels

1953 ◽  
Vol 20 (2) ◽  
pp. 261-269
Author(s):  
M. P. Heisler
Keyword(s):  
Thermal Shock ◽  
Thermal Stresses ◽  
Pressure Vessels ◽  
Transient Temperature ◽  
Thermal Processes ◽  
Integral Theorem ◽  
Dimensionless Stress ◽  
Optimum Heating ◽  
Transient Thermal

Abstract This paper presents the results of computations for determining transient thermal stresses in slabs and circular pressure vessels. The process of solution adopted is to substitute transient-temperature formulas into the already available stress expressions. The expressions for thermal shock are transformed by means of a simple integral theorem into a form appropriate for analyzing the thermal processes commonly used to relieve thermal shock. A new dimensionless stress parameter is defined and applied to the determination of optimum heating or cooling times of massive pressure vessels.

Plastic Deformation of a Solid Cylinder of Temperature Dependent Properties Subjected to Cyclic Loading

1995 ◽  
Author(s):  
Shahriar Jahanian
Keyword(s):  
Cyclic Loading ◽  
Thermal Loading ◽  
Pressure Vessels ◽  
Solid Cylinder ◽  
Temperature Dependent ◽  
Nuclear Fuel Element ◽  
Incremental Growth ◽  
Temperature Dependent Properties ◽  
Transient Thermal ◽  
Structural Behaviors

Abstract There are many practical instances of structural behaviors where the incremental increase of deformation occurs under cyclic loading, such as ratcheting in nuclear fuel element cans, incremental growth of pressure vessels or turbine cases, etc. This increase of deformation may lead to the failure of structure. For an incremental collapse to occur, it is necessary for different parts of the structure to yield at different stages of loading and unloading cycle. When the thermal loading is present, the properties of the material are temperature dependent. Accordingly the yielding occur at the earlier stage. The situation may get worse when the thermal loading is coupled with the mechanical one. This paper presents a quasi-static, uncoupled thermo-elastoplastic analysis based on incremental theory of plasticity. The behavior of a solid cylinder subjected to torsion and transient thermal loading for one cycle is investigated. The influence upon behavior of nonlinear-strain hardening in the material is investigated.

scholarly journals Semi-Analytical Solution of Functionally Graded Circular Short Hollow Cylinder Subject to Transient Thermal Loading

2014 ◽  
Vol 61 (3) ◽  
pp. 409-432 ◽  
Author(s):  
Jafar Eskandari Jam ◽  
Y. Rahmati Nezhad
Keyword(s):  
Analytical Solution ◽  
Hollow Cylinder ◽  
Thermal Loading ◽  
Thermal Stresses ◽  
Functionally Graded ◽  
Thermal Boundary Conditions ◽  
Numerical Laplace Inversion ◽  
Time Variations ◽  
Hollow Cylinders ◽  
Transient Thermal

Abstract In this paper, by using a semi-analytical solution based on multi-layered approach, the authors present the solutions of temperature, displacements, and transient thermal stresses in functionally graded circular hollow cylinders subjected to transient thermal boundary conditions. The cylinder has finite length and is subjected to axisymmetric thermal loads. It is assumed that the functionally graded circular hollow cylinder is composed of N fictitious layers and the properties of each layer are assumed to be homogeneous and isotropic. Time variations of the temperature, displacements, and stresses are obtained by employing series solving method for ordinary differential equation, Laplace transform techniques and a numerical Laplace inversion.

The Influence of the Grade of Materials and their State on the Thermo-Mechanical Behaviour of the Chosen Power Plant Components

2016 ◽  
Vol 250 ◽  
pp. 238-243 ◽  
Author(s):  
Mariusz Twardawa ◽  
Jerzy Okrajni
Keyword(s):  
Mechanical Properties ◽  
Power Plant ◽  
Mechanical Behaviour ◽  
Power Plants ◽  
Thermal Loading ◽  
Stress Strain ◽  
The Real ◽  
Properties Of Materials ◽  
Operation Parameters ◽  
Plant Components

The paper discusses the issue of the influence of the growth of the operation parameters of power plant components on the fatigue phenomena that take place under mechanical and thermal loading. The loading characteristics have been taken as measurements results in industrial conditions. Stress-strain characteristics of such components, which take into consideration the changeable properties of materials subject to fatigue, have been described. The hardening processes of the materials, which are assumed to be used in designed power plants, have also been discussed. The aim of the paper is the description of the mechanical behaviour of the power plant components taking into consideration the real industrial conditions of their operation and changeable mechanical properties of the components’ materials.

Elastoplastic stress and strain predictions for axisymmetric pressure vessel bodies under transient thermal loads

1996 ◽  
Vol 31 (2) ◽  
pp. 81-89 ◽  
Author(s):  
N Adinarayana ◽  
R S Alwar
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Steam Turbine ◽  
Pressure Vessel ◽  
Thermal Loading ◽  
Pressure Vessels ◽  
Approximate Methods ◽  
Valve Body ◽  
Transient Thermal

Evaluation of localized peak strains at stress concentration zones under transient thermal loading is essential for the determination of low cycle fatigue life of a number of pressure vessels like steam turbine components and reactor vessels. Finite element analysis is a powerful technique but there are some difficulties in using the method for inelastic analysis of large-sized components. Several investigators have proposed approximate methods to determine inelastic strains at notches and other stress concentration zones from elastically calculated stress distributions. The accuracy of three of these methods, namely the Neuber rule, the Molski-Glinka rule and GLOSS analysis under thermal loading for axisymmetric pressure vessel bodies was investigated. A parametric study with geometry and material parameters as variables was carried out for three sizes of spheres with nozzles for the determination of peak strains and stresses under transient thermal loading using thermoelastoplastic finite element analyses and also by approximate methods. The same analyses have also been carried out for a steam turbine valve body for the same thermal loading, which is normally encountered by the valve body under start-up conditions. It has been found that GLOSS analysis is more accurate and the use of approximate methods has been recommended, especially for preliminary analyses in the development of new components.

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