The Mechanical Characteristics and Sealing Performance Evaluation of Bolted Pipe Flange Connections With Metallic Flat Gaskets Subjected to Internal Pressure

Bolted pipe flange connections with metallic gaskets have been used under higher pressure as well as higher temperature. However, a few researches on the mechanical characteristics in connections with metallic gaskets have been carried out. It is necessary to examine the mechanical characteristics such as the contact gasket stress distributions which govern the sealing performance, the deformation of the metallic gaskets, changes in axial bolt forces and the hub stress under higher pressure and temperature. In the present paper, the objectives are to examine the changes in axial bolt forces, the hub stress and the contact gasket stress distributions and the sealing performance of the pipe flange connections with metallic flat gaskets. Firstly, the mechanical characteristics of the connections under higher pressure are analyzed using FEA. Then, experiments were carried out to measure the load factor, the hub stress and the leak rate (the sealing performance). The relationship between the average contact gasket stress and the leak rate was measured using platen device at room temperature. The FEA results are fairly coincided with the experimental results. It is shown that the leak rate decreases as the contact gasket stress increases and when the plastic deformation of gaskets occurs, the sealing performance increases. The leak rate was measured in the range of 10−4∼10−7 [Pa·m3/s]. It is found that the sealing performance increases as the gasket width increase in the elastic deformation range while it is independent of the gasket width when the plastic deformation occurs. The effect of temperature on the mechanical characteristics of the connection is also examined. The FEA results are in a fairly good agreement with the experimental results. It is found that the sealing performance increases as the temperature increases. In addition, a method how to determine the bolt preload for increasing the sealing performance is proposed.

Correlation on Scatter Between Torque Coefficient and Bolt Preload in Pipe Flange Connection

In this paper, a mechanism of variation in axial bolt force in pipe flange connection during bolt tightening process is investigated. Especially, Correlation between torque coefficient and bolt preload is investigated. The actual pipe flange connection is tightened by a wrench due to the torque control method. Axial bolt forces were measured in the tightening process. The three types of gasket are chosen in this paper. As a result the good relationships are seen between torque coefficient and axial bolt force. The effect of gasket material on the relationships between torque coefficient and bolt preload is not seen.

Molecular Dynamics Study of Energy Storage Device

Currently, the dominating energy storage device remains the battery, particularly the lithium battery. Lithium/lithium-ion batteries are used for various applications. For example, lithium battery powered pipeline inspection tools are used by the oil and gas industry for internal inspection of pipelines. Lithium batteries are complex devices whose performance optimization requires a good understanding of physical processes that occur on multiple time and length scales. Optimization of the electrolyte, in particular, needs detailed, fundamental, molecular level understanding of the chemical and mechanical features that lead to stable electrolytes such as good interfacial lithium transport properties, thermal stability and safety. In this work, we use molecular dynamics (MD) computational technique to investigate thermodynamic and dynamics properties for various carbonate-based electrolyte systems of lithium-ion batteries.

Reduction of Fugitive Emissions From Bolted Flanged Connections by Using PTFE Blended Gasket

Gasket is the key element which determines the tightness of bolted flanged connection. PTFE blended gaskets which have recently been developed and come onto the market have a superior sealing performance as well as the chemical and temperature resistances and can contribute to reduce fugitive emissions. This paper deals with the sealing behaviors of the PTFE blended gasket and the tightness of a bolted flanged connection in which the gasket is used. The gasket is mainly composed of PTFE and graphite and has a high tightness and heat resistance up to 300 degree C. The creep characteristic is improved by the graphite filler. In this paper, the estimation method of the tightness of bolted flanged connections based on the sealing behavior of gasket is demonstrated. The estimated results are validated by experiments using a flange connection. It is shown that the leak rate below the tightness class 4 defined in the Room Temperature Tightness Test (ROTT, Pressure Vessel Research Council) can be obtained using the PTFE blended gasket.

Comparison of Plastic Collapse Load of Isolated Piping Part and Pipe Run

The analysis of plastic collapse may be used in the fitness-for-service analysis of piping parts. Typically, such an analysis is performed by first determining the loads on the part in question by piping analysis, and then applying the load or load combination to an isolated elastic-plastic model of the part to obtain the collapse load. Plastic load redistribution that would occur if a plastic collapse analysis of the entire pipe run was performed is not considered in the common analysis approach. This paper compares the results of pipe run and piping part plastic collapse analyses for a typical illustrative example under various loading conditions.

Alternative Assembly Evaluation for Railcar Pressure Plate Connection

Alternative assembly procedures and tool improvements have been developed and validated in order to improve the overall safety and efficiency of bolted flanged joint assembly. This is achieved by reducing both the assembly time and any post assembly leaks. Several alternative procedures are documented in ASME PCC-1 Appendix F [1], and usage of these procedures is becoming more common in the process and power industries. Application of these procedures is valid for other industries as well. A test of an alternative assembly procedure for the transportation industry was conducted at a railcar repair facility in Channelview, TX, USA. The evaluation compared alternative vs. legacy assembly procedures and also compared pneumatic tools vs. more traditional hand tools normally used by the mechanics at this facility. Time and effort to assemble the joint were measured and targeted for reduction while also improving worker safety. Five gaskets were tested using materials common for pressure railcar applications and the pressure plate connection. These gaskets included rings made of flexible graphite with metal foil reinforcement, soft skived glass-filled Polytetrafluoroethylene (PTFE), and expanded PTFE with a tang metal core. Various joint assembly combinations of gasket material, assembly pattern, and tool usage were timed and leak tested. A successful assembly met the normal leak test criteria of the shop: the assembled joint was subjected to pressurized air and leaks detected (or not) using a standard leak detection fluid. This performance evaluation was followed with visual inspection and dimensional measurements of the gaskets after removal from the test fixture.

Improvement of Tightening Accuracy of Torque Control Method by Taking Account Geometric Errors in Threaded Fasteners

Torque control method is commonly used when tightening bolted joints because of its easy operation. However, the method involves an essential problem of fairly large scatter in bolt preloads. It has been reported that even if the same torque is applied, bolt preloads show a considerable scatter, e.g., ranging from 25% to 35%. A scatter in coefficients of friction on nut bearing surface and thread pressure flank is a primary source of bolt preload scatter. Meanwhile, the effect of Equivalent Friction Diameter at the bearing surfaces of nut and bolt head cannot be ignored. The scatter in Equivalent Friction Diameter is caused by imperfect geometry, i.e., the flatness deviation at the bearing surfaces. In this paper, the magnitudes of Equivalent Friction Diameter are quantitatively evaluated by FEA, using the experimental data of flatness deviation measured for a number of commercial nuts and bolts. It is shown that the bolt preload is likely to be scattered by as much as plus minus 10% of the target value, owing to the flatness deviation. Based on the comprehensive calculations by considering the imperfect geometry, a strategy to effectively suppress the bolt preload scatter is proposed.

Study of Bolt Tightening Methods Using Load Indicating Bolts

Alternative bolting patterns have been studied and received with wide acceptance for their performance, and are presented in ASME PCC1. However, it seems that the use of the alternative methods has been limited. Users may not have enough confidence to be motivated to use the alternatives. This paper summarizes results of tests on 24” Class 300 flanges tightened by hydraulic torque wrench and pneumatic torque multiplier. The flanges were assembled with two bolting patterns, Legacy pattern and Alternative #3, and their bolt loads were measured using ASTM F2482 load indicating studs. The results may provide validation and supporting information for users who have looked for more time-saving bolting method.

Sealing Properties of Joints Between Metal Surfaces Holding Wavy Defects

Internal sealing of many power plant valves is performed by a metal to metal contact, compatible with severe pressure and temperature conditions of liquid water flow. Contact surfaces are treated by hard alloy coating and lapping in order to enhance sealing properties. However, wavy deformation may occur on the surface because of stress induced during manufacturing and all through the device life, for example as a consequence of thermal shocks. We aim to quantitatively correlate the leakage which results from wavy defects through experimental measurements and predictions obtained from modeling. In order to leave as few uncontrolled parameters as possible, the sealing joint is isolated from the valve device as a separate system consisting of a flat and rigid plug and an annular seat holding a wavy defect. The leak sealing properties of the metal to metal contact are expressed by a transmissivity value. This physical quantity has a length cube dimension and relates flow rate to pressure difference by a linear relation. It is intrinsic to the interstitial geometry. The experimental section of this paper relies on two key steps. First, a sample seat, holding a controlled wavy defect, is manufactured. This is achieved by elastically deforming a cylindrical metal part having a tube shape in a lathe’s mandrel. The end-face is machined, lapped and finally the part is released, leaving a wavy defect on the end-face as a consequence of elastic relaxation. Secondly, the transmissivity of the sample seat, pressed against a flat, rigid plug, is determined from leak rate and fluid pressure measurements carried out on specific experimental devices. The procedure is repeated for several clamping loads yielding the transmissivity to apparent contact pressure dependence. In the modeling section, leakage is calculated following three successive main stages. In the whole procedure, the flow action on the structure is neglected. First a geometrical model of the seat holding the manufactured wavy defect is built using a linear modal decomposition on a basis of vibrational eigen modes allowing to represent any kind of defect. Secondly, the remaining open space -i.e. the opening between the plug and seat surfaces-resulting from the clamping force normal to the mean plane of the contact, is computed. A finite element model is used to solve the contact problem on the non-trivial form of the wavy defect on the whole 3D geometry. Finally, the transmissivity is computed by solving the Reynolds equation for incompressible flow within the percolating opening between the plug and the seat. The final result of the modeling section is a transmissivity function of the apparent contact pressure, characterizing the leakage of the given wavy defect on the seat. Predictions of the transmissivity reveal to be in good agreement with that obtained experimentally at low clamping forces and overestimate the leakage for larger ones.