Effect of Bolt Spacing on the Circumferential Distribution of Gasket Contact Stress in Bolted Flange Jonts

2008 ◽  
Author(s):  
Tan Dan Do ◽  
Abdel-Hakim Bouzid ◽  
Thien-My Dao
Keyword(s):  
Contact Stress ◽  
Potential Risk ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Critical Value ◽  
Load Increase ◽  
Circumferential Distribution ◽  
Maintenance Work ◽  
Bolted Flange ◽  
Bolt Spacing

Bolted flange joints are part of pressure vessel and piping components and are used extensively in the chemical, petrochemical and nuclear power industries. They are simple structures and offer the possibility of disassembly which make them attractive to connect pressurized equipments and piping. In addition of being prone to leakage, they often require maintenance while in operation in which case the bolts are either retightened as in hot torquing or untightened to be replaced. Although costly shutdown are avoided, such a maintenance work exposes the operator to a potential risk because the bolt load alteration can produce a gasket load unbalance which results in a local gasket contact stress to drop below some critical value causing major leak and hence jeopardizing the life of the operator. This paper addresses the issue of the contact stress level unbalance around the flange when the bolts are subjected to bolt-up condition. This study is developed for the purpose of helping limit the degree of load increase in hot torquing or the maximum number of bolts to be replaced at a time and identify those flanges the bolt of which cannot be replaced in service.

Effect of Bolt Spacing on the Circumferential Distribution of the Gasket Contact Stress in Bolted Flange Joints

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Tan Dan Do ◽  
Abdel-Hakim Bouzid ◽  
Thien-My Dao
Keyword(s):  
Elastic Foundation ◽  
Contact Stress ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Element Model ◽  
Foundation Model ◽  
Load Increase ◽  
Maintenance Work ◽  
Bolted Flange ◽  
Bolt Spacing

Bolted flange joints are part of pressure vessel and piping components and are extensively used in the chemical, petrochemical, and nuclear power industries. They are simple structures and offer the possibility of disassembly, which makes them attractive to connect pressurized equipment and piping. In addition to being prone to leakage, they often require maintenance while in operation in which case the bolts are either retightened as in hot torquing or untightened to be replaced. Although costly shutdowns are avoided, such maintenance work exposes the operator to a potential risk because the bolt load alteration can produce a gasket load unbalance, which results in the local gasket contact stress to drop below some critical value, causing major leak and hence jeopardizing the life of the worker. This paper addresses the issue of the contact stress level unbalance around the flange when the bolts are subjected to initial tightening. The study compares the contact stress distribution variations, an analytical developed model based on the theory of rings on elastic foundation, to those given by the finite element model and the simple beam on elastic foundation model developed by Koves (2007, “Flange Joint Bolt Spacing Requirements,” Proceedings of PVP2007, ASME Pressure Vessel and Piping Division Conference). This study is developed for the purpose of helping limit the degree of load increase in hot torquing or the maximum number of bolts to be replaced at a time and identify those flanges for which the bolt cannot be replaced in service.

On the Use of Theory of Rings on Nonlinear Elastic Foundation to Study the Effect of Bolt Spacing in Bolted Flange Joints

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Tan Dan Do ◽  
Abdel-Hakim Bouzid ◽  
Thien-My Dao
Keyword(s):  
Elastic Foundation ◽  
Contact Stress ◽  
Large Diameter ◽  
Pressure Vessels ◽  
Element Analysis ◽  
Linear Elastic ◽  
Circumferential Distribution ◽  
Bolted Flange ◽  
Nonlinear Elastic ◽  
Bolt Spacing

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; the flange and gasket stiffness and bolt spacing design combination being one of them. In our recent paper, the effects of bolt spacing were investigated based on the theory of circular beams resting on a linear elastic foundation (Do, T. D., Bouzid, A. H., and Dao, T.-M., 2011, “Effect of Bolt Spacing on the Circumferential Distribution of Gasket Contact Stress in Bolted Flange Joints,” ASME J. Pressure Vessel Technol., 133 (4), 041205). This paper is an extension of the work in which an analytical solution based on the real nonlinear gasket behavior is developed. This study focuses on the distribution of the gasket contact stress of two large diameter flanges, namely, a 52 in. and a 120 in. heat exchanger (HE) flanges. The nonlinear gasket behavior solution is compared to the Finite Element Analysis (FEA) and the linear gasket behavior solution for evaluation and comparison.

On the Effect of External Bending Loads in Bolted Flange Joints

2007 ◽  
Author(s):  
Abdel-Hakim Bouzid ◽  
Yves Birembaut ◽  
Hubert Lejeune
Keyword(s):  
Analytical Model ◽  
Contact Stress ◽  
Analytical Approach ◽  
Bolted Joint ◽  
Acceptable Solution ◽  
Sealing Performance ◽  
Circumferential Distribution ◽  
Bending Loads ◽  
Minimum Stress ◽  
Bolted Flange

Most current flange design methods use an equivalent pressure to treat bolted flange connections subjected to external bending loads. This oversimplified approach together with the lack of a proper assessment of the actual affected tightness make these methods inadequate for modern flange design. The substitution of the external applied moment by an equivalent pressure is excessively conservative and not realistic since it assumes that the achieved tightness is that of a gasket unloaded entirely to a minimum stress whereas in reality only a small section of it is, the rest of it is actually at a much higher stress. The successfulness of a valid analytical approach in yielding to an acceptable solution resides in its ability to account for the circumferential distribution of the gasket contact stress and its effect on leakage. This paper presents an analytical model based on the flexibility of the flange to treat flanges subjected to bending loads such as those produced by external moments and misalignments and capable of integrating leakage around the gasket circumference. The bolted joint sealing performance in the presence of such loads is evaluated using the new PVRC gasket constants Gb, a and Gs obtained from ROTT tests. The analytical results including leakage predictions are validated by comparison to those obtained numerically by FEA and experimentally on different size flanges. The over-conservatism of the equivalent pressure is demonstrated.

FEM Stress Analysis and Sealing Performance in Bolted Flange Connections With Cover of Pressure Vessel Subjected to Internal Pressure

2003 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Rie Higuchi
Keyword(s):  
Internal Pressure ◽  
Contact Stress ◽  
Pressure Vessel ◽  
The Finite Element Method ◽  
Flange Connection ◽  
Bolt Preload ◽  
Sealing Performance ◽  
Bolted Flange ◽  
Contact Stress Distribution ◽  
Spiral Wound

The stresses of a bolted flange connection with a cover of pressure vessel (CPV) in which a spiral wound gasket is inserted, under internal pressure are analyzed taking account a hysteresis of the gasket by using the finite element method (FEM). The leakage tests were also conducted using an actual bolted flange connection with a CPV with a spiral wound gasket. Using the contact stress distribution of the bolted flange connection with a CPV under internal pressure and the tightness parameter, the values of the new gasket constants were obtained by taking into account the changes in the contact stress. A difference in the new gasket constants between the estimated values obtained from the actual bolted flange connection with a CPV and the values obtained by the PVRC procedure was small. In addition, a method to determine the bolt preload for a given tightness parameter was demonstrated. The obtained results of the bolt preload for the bolted flange connection with a CPV were in a fairly good agreement with those obtained by the PVRC procedure under a lower pressure application. However, a difference in the bolt preload was about 7% when the internal pressure was increased.

Development of a New Bolt Spacing Formula

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Tan Dan Do ◽  
Abdel-Hakim Bouzid ◽  
Thien-My Dao
Keyword(s):  
Elastic Foundation ◽  
Contact Stress ◽  
Compression Modulus ◽  
Pressure Vessels ◽  
Linear Elastic ◽  
Flange Thickness ◽  
Bolted Flange ◽  
Nonlinear Elastic ◽  
The Relationship ◽  
Bolt Spacing

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential directions. Many factors contribute to such a failure; the flange and gasket stiffness, bolt spacing or a combination of them are to name a few. In our recent papers, the effect of bolt spacing was investigated based on the theory of circular beams on linear elastic foundation and on the theory of rings on nonlinear elastic foundation. The variations of the contact stress between bolts were of a concern. This paper is an extension of the work in which an analytical solution, based on the theory of circular beams resting in a linear elastic foundation, has been developed to determine a formulae for flange bolt spacing. The relationship between bolt spacing, gasket compression modulus, and flange thickness is deduced from an analysis that considers a maximum tolerated gasket contact stress difference between any two bolts.

On the Development of a New Bolt Spacing Formula

2012 ◽  
Author(s):  
Tan Dan Do ◽  
Abdel-Hakim Bouzid ◽  
Thien-My Dao
Keyword(s):  
Elastic Foundation ◽  
Contact Stress ◽  
Compression Modulus ◽  
Pressure Vessels ◽  
Stress Difference ◽  
Linear Elastic ◽  
Flange Thickness ◽  
Bolted Flange ◽  
The Relationship ◽  
Bolt Spacing

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a non-uniform distribution of gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; the flange and gasket stiffness and bolt spacing design combinations being a couple of them. In our recent papers the effects of bolt spacing was investigated based on the theory of circular beams resting on a linear elastic foundation and based on the theory of ring on non-linear elastic foundation. The variations of the contact stress between bolts were of a concern. This paper is an extension of the work in which an analytical solution based on the theory of circular beams resting on a linear elastic foundation has been developed to determine flange bolt spacing. The relationship between bolt spacing, gasket compression modulus and flange thickness is deduced from an analysis that considers a maximum tolerated gasket contact stress difference between any two bolts.

Development of an Integrity Evaluation System on the Basis of Cooperative Virtual Reality Environment for Nuclear Power Plant

2004 ◽  
Author(s):  
J. C. Kim ◽  
J. B. Choi ◽  
Y. H. Choi
Keyword(s):  
Virtual Reality ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Pressure Vessel ◽  
Evaluation System ◽  
Nuclear Power ◽  
Structural Integrity ◽  
Reactor Pressure Vessel ◽  
Virtual Reality Environment ◽  
Reactor Pressure

Since early 1950’s fracture mechanics has brought significant impact on structural integrity assessment in a wide range of industries such as power, transportation, civil and petrochemical industries, especially in nuclear power plant industries. For the last two decades, significant efforts have been devoted in developing defect assessment procedures, from which various fitness-for-purpose or fitness-for-service codes have been developed. From another aspect, recent advances in IT (Information Technologies) bring rapid changes in various engineering fields. IT enables people to share information through network and thus provides concurrent working environment without limitations of working places. For this reason, a network system based on internet or intranet has been appeared in various fields of business. Evaluating the integrity of structures is one of the most critical issues in nuclear industry. In order to evaluate the integrity of structures, a complicated and collaborative procedure is required including regular in-service inspection, fracture mechanics analysis, etc. And thus, experts in different fields have to cooperate to resolve the integrity problem. In this paper, an integrity evaluation system on the basis of cooperative virtual reality environment for reactor pressure vessel which adapts IT into a structural integrity evaluation procedure for reactor pressure vessel is introduced. The proposed system uses Virtual Reality (VR) technique, Virtual Network Computing (VNC) and knowledge based programs. This system is able to support 3-dimensional virtual reality environment and to provide experts to cooperate by accessing related data through internet. The proposed system is expected to provide a more efficient integrity evaluation for reactor pressure vessel.

The method for calculating the probability of brittle destruction of NPP equipment in different operating modes with postulated defectiveness

2021 ◽  
Vol 14 (1) ◽  
pp. 34-39
Author(s):  
D. A. Kuzmin ◽  
A. Yu. Kuz’michevskiy
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Power Plants ◽  
Reactor Pressure Vessel ◽  
Practical Significance ◽  
Reactor Unit ◽  
Operating Modes ◽  
Brittle Destruction ◽  
Reactor Pressure

The destruction of equipment metal by a brittle fracture mechanism is a probabilistic event at nuclear power plants (NPP). The calculation for resistance to brittle destruction is performed for NPP equipment exposed to neutron irradiation; for example, for a reactor plant such as a water-water energetic reactor (WWER), this is a reactor pressure vessel. The destruction of the reactor pressure vessel leads to a beyond design-basis accident, therefore, the determination of the probability of brittle destruction is an important task. The research method is probabilistic analysis of brittle destruction, which takes into account statistical data on residual defectiveness of equipment, experimental results of equipment fracture toughness and load for the main operating modes of NPP equipment. Residual defectiveness (a set of remaining defects in the equipment material that were not detected by non-destructive testing methods after manufacturing (operation), control and repair of the detected defects) is the most important characteristic of the equipment material that affects its strength and service life. A missed defect of a considerable size admitted into operation can reduce the bearing capacity and reduce the time of safe operation from the nominal design value down to zero; therefore, any forecast of the structure reliability without taking into account residual defectiveness will be incorrect. The application of the developed method is demonstrated on the example of an NPP reactor pressure vessel with a WWER-1000 reactor unit when using the maximum allowable operating loads, in the absence of load dispersion in different operating modes, and taking into account the actual values of the distributions of fracture toughness and residual defectiveness. The practical significance of the developed method lies in the possibility of obtaining values of the actual probability of destruction of NPP equipment in order to determine the reliability of equipment operation, as well as possible reliability margins for their subsequent optimization.

Development of a Fatigue Design Curve for Austenitic Stainless Steels in LWR Environments: A Review

2002 ◽  
Author(s):  
Omesh K. Chopra
Keyword(s):  
Stainless Steels ◽  
Pressure Vessel ◽  
Type Strain ◽  
Nuclear Power ◽  
Austenitic Stainless Steels ◽  
Environmental Parameters ◽  
Light Water Reactor ◽  
Code Design ◽  
Fatigue Design ◽  
Asme Code

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components and specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain–vs.–life (ε–N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This paper reviews the existing fatigue ε–N data for austenitic stainless steels in LWR coolant environments. The effects of key material, loading, and environmental parameters, such as steel type, strain amplitude, strain rate, temperature, dissolved oxygen level in water, and flow rate, on the fatigue lives of these steels are summarized. Statistical models are presented for estimating the fatigue ε–N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue design curves.

Reactor Pressure Vessel Modification Approaches

2005 ◽  
Author(s):  
Ronald J. Payne ◽  
Stephen Levesque
Keyword(s):  
Pressure Vessel ◽  
Nuclear Power ◽  
State Of The Art ◽  
Electrical Power ◽  
Evaluation Criteria ◽  
Reactor Pressure Vessel ◽  
Alloy 600 ◽  
Electrical Power Research Institute ◽  
Reactor Pressure ◽  
Plant Components

Stress corrosion cracking of Alloy 600 has lead to the modification and replacement of many nuclear power plant components. Among these components are the Bottom Mounted Nozzles (BMN) of the Reactor Pressure Vessel (RPV). Modifications of these components have been performed on an emergent basis. Since that time, Framatome ANP has developed state-of-the-art modification methods for the repair of BMNs using the Electrical Power Research Institute (EPRI) managed Materials Reliability Program (MRP) attributes for an ideal repair as a basis for evaluation of modification concepts. These attributes were used to evaluate the optimal modification concepts and develop processes and tooling to support future modification activity. This paper details the BMN configurations, modification evaluation criteria, several modification concepts, and the development of the tooling to support the optimal modification scenarios.

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