Procedure to Guarantee Tightness of Bolted Flange Connections of Floating Type With Two Gaskets

2009 ◽  
Author(s):  
Lubomir Junek ◽  
Jaroslav Bartonicek ◽  
Milan Vrana
Keyword(s):  
Internal Pressure ◽  
Local Stress ◽  
Life Time ◽  
Pressure Vessels ◽  
Relaxation Behaviour ◽  
Plastic Deformations ◽  
Elastic Plastic ◽  
Time Extension ◽  
Assembly Procedure ◽  
Selection Of

To consider special demands, two gaskets floating between the flange faces are used for example in flanged connections of pressure vessels, valves, pumps etc. Tightness control can be one of the reasons to choose this design. The inner (primary) gasket has to tighten the internal pressure; the outer (secondary) gasket tightens possible leakage of the primary gasket. By the use of two identical gaskets in the same plane the procedure for the tightness proof is the same as in connections with one gasket. In many cases there are used two gaskets with different characteristics (deformation and tightness characteristics) in two tightening planes. The behaviour of this connection depends not only on the gasket characteristics but also on the tolerances of axial dimensions. The distribution of prestress on both gaskets is determined by the elastic-plastic deformations of both gaskets and tolerances of axial dimensions of the connection. The decrease of gasket stress in operation depends on the plastic deformations of both gaskets in operation, too. Depending on the demanded tightness class, the possible gasket stress during assembly and the gasket stress in operation determine the selection of suitable gaskets (with necessary gasket characteristics). It is necessary to take into account the internal pressure and possible pressure between primary and secondary gasket, too. In the paper the design of gaskets for this type of connection is discussed. Originally, it was used: - nickel ring as primary gasket, - asbestos packing as secondary gasket. Both gaskets have suitable deformation characteristics for the existing type of connection. The secondary gasket has low stiffness for the adjustment of an optimal stress on the primary gasket after prestressing. The primary gasket has a good relaxation behaviour. However, the nickel ring needs a very high local stress to achieve suitable tightness behaviour. This stress leads to plastic deformation of the flange surface during assembly, too, and this can induce leakage after the next assembly (with new rings) as operation experience showed. The use of asbestos packing is not allowed any more due to health reasons. This invoked a redesign of this gasket. The paper deals with gasket proofs and gasket characteristics for selection of suitable gaskets. Calculations of gasket stress distributions of both gaskets (elastic-plastic deformations) are presented. The analysis of the stress distribution allows reviewing the tightness class in operation incl. relaxation behaviour of the connection. Other recommendations are listed like the increase of connection safety by a reduction of bolt stiffness (better relaxation behaviour of the connection and higher bolt elongation), more accurately bolt elongation measurement, new assembly procedure, etc. Main target of the re-design is life time extension of connection, too.

Elastic-Plastic Stress Analysis of Pressure Vessels

2012 ◽  
Author(s):  
Yang-chun Deng ◽  
Gang Chen
Keyword(s):  
Internal Pressure ◽  
Stress Analysis ◽  
Strain Hardening ◽  
Pressure Vessel ◽  
Plastic Instability ◽  
Pressure Vessels ◽  
Structural Deformation ◽  
Elastic Plastic ◽  
Thin Walled ◽  
Plastic Stress

To save material, the safety factor of pressure vessel design standards is gradually decreased from 5.0 to 2.4 in ASME Boiler and Pressure Vessel Codes. So the design methods of pressure vessel should be more rationalized. Considering effects of material strain hardening and non-linear structural deformation, the elastic-plastic stress analysis is the most suitable for pressure vessels design at present. This paper is based on elastic-plastic theory and considers material strain hardening and structural deformation effects. Elastic-plastic stress analyses of pressure vessels are summarized. Firstly, expressions of load and structural deformation relationship were introduced for thin-walled cylindrical and spherical vessels under internal pressure. Secondly, the plastic instability for thin-walled cylindrical and spherical vessels under internal pressure were analysed. Thirdly, to prevent pressure vessels from local failure, the ductile fracture strain of materials was discussed.

scholarly journals POSSIBILITY OF A LIFE-TIME EXTENSION FOR WWER-1000 REACTOR PRESSURE VESSELS BEYOND THE DESIGN PERIOD

2020 ◽  
Vol 1 (60) ◽  
pp. 103-108
Author(s):  
M. Holiak ◽  
◽  
V. Revka ◽  
L. Chyrko ◽  
O. Trygubenko ◽  
...  
Keyword(s):  
Life Time ◽  
Pressure Vessels ◽  
Time Extension ◽  
Reactor Pressure

Thermal Annealing of Reactor Pressure Vessels

2015 ◽  
Author(s):  
Mikhail A. Sokolov ◽  
William L. Server ◽  
Randy K. Nanstad
Keyword(s):  
Thermal Annealing ◽  
Nuclear Power ◽  
Power Plants ◽  
Temperature Shift ◽  
Life Time ◽  
Pressure Vessels ◽  
Operating Life ◽  
Time Extension ◽  
High Doses ◽  
Reactor Pressure

Some of the current fleet of nuclear power plants is poised to reach their end of life and will require an operating life time extension. Therefore, the main structural components, including the reactor pressure vessel (RPV), will be subject to higher neutron exposures than originally planned. These longer operating times raise serious concerns regarding our ability to manage the reliability of RPV steels at such high doses. Thermal annealing is the only option that can, to some degree, recover irradiated beltline region transition temperature shift and recover upper shelf energy properties lost during radiation exposure and extend RPV service life. This paper reviews the experience accumulated internationally with development and implementation of thermal annealing to RPV and potential perspectives for carrying out thermal annealing on US nuclear power plant RPVs.

Stress Analysis on New Multilayer Cylinder With Use of Thin Inner Shell and Cross-Helical Wound Shaped-Steel Ribbon for Pressure Vessels

2013 ◽  
Author(s):  
Ping Chen ◽  
Shuilian Chen
Keyword(s):  
Internal Pressure ◽  
Stress Analysis ◽  
Thin Shell ◽  
Pressure Vessels ◽  
Multilayer Cylinder ◽  
Elastic Plastic ◽  
New Type ◽  
Steel Ribbon

In this paper, a stress analysis on a new type of multilayer cylinder using thin shell and cross-helically interlocked shaped-steel ribbon wound layers is carried out under the action of internal pressure based on the elastic and elastic-plastic mechanics.

Elastic-Plastic Analysis of Functionally Graded Spherical Pressure Vessels Using Strain Gradient Plasticity

2017 ◽  
Vol 09 (08) ◽  
pp. 1750118 ◽  
Author(s):  
Hassan Shokrollahi
Keyword(s):  
Internal Pressure ◽  
Strain Gradient ◽  
Plastic Region ◽  
Pressure Vessels ◽  
Functionally Graded ◽  
Strain Gradient Plasticity ◽  
Gradient Plasticity ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Spherical Pressure

In this paper, formulation of elastic-plastic analysis of functionally graded (FG) spherical pressure vessels under internal pressure based on strain gradient plasticity is presented. The material properties are assumed to vary in a power law manner in the radial direction. A linear hardening rule for the material behavior in the plastic region is assumed. After deriving the governing differential equations, a closed form solution is obtained. At the first step, the obtained results were validated against other available results in the literature. Then the effects of changing the inner radius from a few micro-meters to one meter, FG power index and strain gradient coefficient on stress and plastic region size are studied based on classical and strain gradient theories. Also, the effect of internal pressure on the size of plastic region is studied.

Application of Elastic-Plastic Methods to Delayed Coker Drum Design

2011 ◽  
Author(s):  
John J. Aumuller ◽  
Zihui Xia ◽  
Feng Ju
Keyword(s):  
Oil Sands ◽  
Thermal Stresses ◽  
Liquid Product ◽  
Base Material ◽  
Local Stress ◽  
Pressure Vessels ◽  
Cold Spot ◽  
Elastic Plastic ◽  
The Impact ◽  
Spot Formation

Coke drums are pressure vessels that are used in oil sands and conventional refinery processing industries for the thermal cracking of reduced bitumen to recover additional, saleable gas and liquid product streams. The drums are constructed to the requirements of ASME VIII Division 1 although they are in a low cycle thermal-mechanical service environment. Recent practice has been to introduce design by analysis considerations from ASME VIII Division 2 even though service temperatures of the actual equipment exceed the design limits of the Code. In this paper, simplified elastic-plastic analysis models are developed for assessment of the stress and strain levels in coke drums during specific operational phases. One model is applied for determination of the local stress caused by differences in the coefficients of thermal expansion between the clad liner and base materials. Because clad construction is used throughout the vessel, the impact is extensive. Consideration is given to the general stresses induced by the cyclical, progressive dilation and contraction action of the drum shell caused by axial thermal gradients. Another model estimates hot and cold spot formation and the development of localized stress / strain distributions in coke drums. The resulting thermal stresses include the local stress from suppression of differential expansion between clad and base material, thermal bending stresses and local thermal stresses from hot and cold spot formation. It is found that the evaluation of these loads on drum cracking aligns with industry survey results. Better understanding of these loads has impact on materials selection and fabrication procedures for new drums and repair of existing drums. Operational considerations can also be identified to help improve drum reliability.

Stresses at openings in the torispherical end closure of a pressure vessel

1973 ◽  
Vol 8 (3) ◽  
pp. 191-199 ◽  
Author(s):  
R Kitching ◽  
K T Lau
Keyword(s):  
Stress Distribution ◽  
Internal Pressure ◽  
Pressure Vessel ◽  
Elastic Stress ◽  
Pressure Vessels ◽  
Plastic Limit ◽  
Plastic Deformations ◽  
Elastic Stresses ◽  
Pressure Test ◽  
Plastic Limit Pressure

In the design of torispherical heads for cylindrical pressure vessels, it would often be desirable to position openings or branch connections in the vicinity of the toroidal portion of the shell, but from strength considerations it is normal practice to avoid doing so. An 18 inch inside-diameter model vessel of this type, with a nominal inside toroidal radius of 1.25 in was used for making strain and hence stress measurements in the shell due to internal pressure. Four unreinforced openings of 3 inch diameter were placed at different positions in the torispherical end and an elastic stress distribution for the shell around each opening was obtained. Distributions of elastic stresses in the shell were compared for the different opening positions with those in the unpierced shell in the toroidal region. Plastic deformations were measured in an over-pressure test and a plastic limit pressure was estimated.

scholarly journals Symmetric Nature of Stress Distribution in the Elastic-Plastic Range of Pinus L. Pine Wood Samples Determined Experimentally and Using the Finite Element Method (FEM)

Symmetry ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 39
Author(s):  
Łukasz Warguła ◽  
Dominik Wojtkowiak ◽  
Mateusz Kukla ◽  
Krzysztof Talaśka
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Stress Distribution ◽  
Moisture Content ◽  
Tool Geometry ◽  
Wood Fibers ◽  
Data Set ◽  
Plastic Deformations ◽  
Pine Wood ◽  
Elastic Plastic

This article presents the results of experimental research on the mechanical properties of pine wood (Pinus L. Sp. Pl. 1000. 1753). In the course of the research process, stress-strain curves were determined for cases of tensile, compression and shear of standardized shapes samples. The collected data set was used to determine several material constants such as: modulus of elasticity, shear modulus or yield point. The aim of the research was to determine the material properties necessary to develop the model used in the finite element analysis (FEM), which demonstrates the symmetrical nature of the stress distribution in the sample. This model will be used to analyze the process of grinding wood base materials in terms of the peak cutting force estimation and the tool geometry influence determination. The main purpose of the developed model will be to determine the maximum stress value necessary to estimate the destructive force for the tested wood sample. The tests were carried out for timber of around 8.74% and 19.9% moisture content (MC). Significant differences were found between the mechanical properties of wood depending on moisture content and the direction of the applied force depending on the arrangement of wood fibers. Unlike other studies in the literature, this one relates to all three stress states (tensile, compression and shear) in all significant directions (anatomical). To verify the usability of the determined mechanical parameters of wood, all three strength tests (tensile, compression and shear) were mapped in the FEM analysis. The accuracy of the model in determining the maximum destructive force of the material is equal to the average 8% (for tensile testing 14%, compression 2.5%, shear 6.5%), while the average coverage of the FEM characteristic with the results of the strength test in the field of elastic-plastic deformations with the adopted ±15% error overlap on average by about 77%. The analyses were performed in the ABAQUS/Standard 2020 program in the field of elastic-plastic deformations. Research with the use of numerical models after extension with a damage model will enable the design of energy-saving and durable grinding machines.

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