Toshiyuki Sawa

FEM Stress Analysis and Sealing Performance in Pipe Flange Connections With Gaskets Subjected to External Bending Moment: Case Where Internal Fluid is Liquid

The leakage evaluation when gas is used is more severe than that when liquid is used in pipe flange connections. In a practical design, it is also necessary to examine the leakage in the connection under liquid internal pressure. This paper deals with the contact gasket stress distributions in the pipe flange connections with a spiral wound gasket and a compressed sheet gasket by using elasto-plastic finite element method (FEM) taking account hysteresis and non-linearity in the stress-strain curves of the gaskets, when bending moments as well as internal pressure are applied to the connections. In the FEM calculations, the effects of the gaskets and the initial clamping bolt force (bolt preload) on the contact gasket stress distributions are examined. The leakage tests for the connections under bending moments were also conducted by using liquid (water). By using the results of the leakage tests and the calculated contact gasket stress distributions, the sealing performance of the connections is evaluated. It is found that the sealing performance of the connection under the bending moment can be estimated when internal fluid is liquid (water).Copyright

Thermal Stress Analysis and Sealing Performance Evaluation of Pipe Flange Connections With Spiral Wound Gaskets Under Elevated Temperature

In this paper, the thermal stress distributions at the interfaces between pipe flanges and the gasket under elevated temperature and internal pressure were calculated by using the finite element method (FEM) taking into account hysteresis in the stress-strain curves of spiral wound gasket. Leakage tests were performed using helium gases. In addition, the effects of temperature on the sealing performance were examined by using an actual pipe flange connection with spiral wound gasket under elevated temperature. By using the calculated contact stress distributions and the results of the leakage tests, the sealing performance was evaluated.Copyright

A New Design Method for Piping Components Against Leakage and Damage Subjected to High Level Earthquake Load

A design method of piping components for Level 2 earthquake (the possible strongest earthquake with extremely low probability of occurrence) such as bolted flanged joints, expansion joints, and equipment nozzles is described. This design method is provided taking into account their failure modes and degree of safety. The failure modes for each piping component is classified according to the past damage experience due to earthquake, and each criterion is provided against the failure mode. The typical failure modes are gas leakage, fatigue failure, cumulative plastic deformation during and after earthquake for bolted flanged joints, expansion joints and equipment nozzles in piping components, respectively. Specifically, the simplified method of bolted flanged joints is proposed as the convenient design method for chemical plants and petroleum refineries, etc. (here in after calls as plant) The method is derived using gasket factor, gasket dimensions and clamping forces due to bolts for external piping load. This practical method is investigated and verified due to the experimental results on the welding neck type flanges subjected to static bending moment, in which the bolted flanged joints of NPS 4″ and 8″ in size, 3 types of gaskets are used. In addition, the dynamic inertia force effect is also studied by the shaking table tests using cantilever model of bolted flanged joints at fixed side with changing the bolt clamping forces and gasket types.Copyright

Effects of Scatter in Bolt Preload of Pipe Flange Connections With Gaskets on Sealing Performance

It has been well known that a scatter in axial bolt forces of pipe flange connections tightened by the torque control method is substantial. It is necessary for evaluating the sealing performance of the pipe flange connections with the gaskets subjected to intemal pressure to know the contact gasket stress distributions due to the scatter of the axial bolt forces in the connections tightened by the torque control method. This paper deals with the leakage of the pipe flange connections with a spiral wound gasket and that with a compressed sheet gasket tightened by the torque control method. The scatter in the axial bolt forces was measured in the experiments. The contact gasket stress distributions at the interfaces of the pipe flange connections with the gaskets were calculated under the measured axial bolt forces by using elasto-plastic finite element method (FEM) taking into account hysteresis and non-linearity in the stress-strain curves of the gaskets. The effects of the scatter in the axial bolt forces tightened by the torque control method on the gas leakage were also examined by using the actual pipe flange connections. As the result, a difference in an amount of gas leakage measured was found to be substantial between our study and PVRC procedure. By using the calculated contact gasket stress distributions under the internal pressure and the results of the leakage tests, the sealing performance was evaluated. It is found that the sealing performance is worse in the actual pipe flange connection than that evaluated by PVRC procedure.© 2003 ASME

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

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.Copyright

Stress Analysis and Sealing Performance Evaluation in Non-Circular Flange Connections With Gaskets Subjected to Internal Pressure

The contact gasket stress distributions of a non-circular flange connection with a compressed asbestos sheet gasket subjected to internal pressure were analyzed taking into account of the hysteresis behaviors of the gasket by using the finite element method (FEM). Leakage tests were also conducted using an actual non-circular flange connection with a compressed asbestos sheet gasket under internal pressure. Using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants between the values obtained from the present study and those by the PVRC procedure was substantial. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated.Copyright

FEM Stress Analysis and the Sealing Performance Evaluation in Stainless Steel Elbow and Tee Fittings Under Internal Pressure: Case Where Internal Fluid is Liquid

Stainless steel fittings such as elbows, tees, nipples and so on have been widely used in mechanical structures and chemical plants, it is well known that the leakage in the fittings used sealing tapes is less than that without the sealing tapes. In a practical design, it is necessary to examine the stress states and the leakage in the fittings under internal pressure and external loads such as tensile loads, bending moments and so on. This paper deals with the FEM stress analysis of the fittings subjected to internal pressure. In the FEM calculations, the engaged screw threads are taken into consideration as helical threads in the three-dimension. The leakage tests for the fittings under internal pressure were also conducted by using liquid (oil). Using the results of the leakage tests and the calculated stress states in the fittings, the sealing performance of the fittings under internal pressure was evaluated and the effect of the tightening torque was clarified on the sealing performance. In addition, the numerical results were compared with the experimental results. As the result, the effects of the sealing tapes on the contact stress distributions were also clarified.Copyright

Effects of Scatter in Bolt Preload of Pipe Flange Connections With Spiral Wound Gaskets Under Internal Pressure: In Case of Larger Pipe Flange Connection With 20[quotation mark] Nominal Diameter

It has been well known that a scatter in axial bolt forces of pipe flange connections tightened by the torque control method is substantial. In practice, pipe flange connections with the larger nominal diameter tightened by the torque control method have been used, frequently. So, in an optimum design of pipe flange connections with gaskets, it is necessary to understand the characteristics of the pipe flange connections with larger nominal diameter under internal pressure and the contact gasket stress distributions due to the scatter of the axial bolt forces in the connections tightened by the torque control method. In this paper, the leakage tests were performed in the actual larger pipe flange connections with 20” nominal diameter using helium gas. Then, the effects of the scatter in the axial bolt forces tightened by the torque control method on the gas leakage were also examined. By using the calculated contact stress distributions and the results of the leakage tests, the sealing performance was evaluated.Copyright

Finite Element Stress Response Analysis of Stepped-Lap Adhesive Joints of Similar Adherends Under Impact Tensile Loadings

The stress variations and stress distributions in stepped-lap adhesive joints of similar adherends under impact tensile loadings were analyzed in elastic range using three-dimensional finite element method (DYNA3D). The impact loadings were applied to the lower adherend by dropping a weight. The stress distributions in stepped-lap adhesive joints of similar adherends under static tensile loadings were also analyzed using FEM (MARC). The effects of Young’s modulus of the adherends, the adhesive thickness, and a number of steps in the adherends on the stress variations and the stress distributions at the interfaces between the adherends and the adhesive were examined under both impact and static loadings. As the results, it was found that (1) the maximum value of the maximum principal stress σ1 occured at the outside edge of the butted interface between the adhesive and the lower adherend to which impact loadings were applied; (2) The maximum value of stress σ1 increased as Young’s modulus of the adherends increased; (3) The maximum value of stress σ1 increased as the adhesive thickness decreased, and it increased at the butted parts of joints as the adhesive thickness decreased. The maximum value of stress σ1 increased at the lapped parts of joints as the adhesive thickness increased; (4) The maximum value of stress σ1 increased as the numbers of steps in the adherends increased. The characteristic of the joints under static loadings were also clarified. In addition, the experiments to measure the strain response of joints subjected to impact tensile loadings were carried out using strain gauges. A fairly good agreement was found between the numerical and the measured results concerning the strain responses.Copyright

Finite Element Stress Response Analysis of Butt Adhesive Joints of Hollow Cylinders Subjected to Impact Bending Moments

The stress variation in butt adhesive joints of hollow cylinders subjected to impact bending moments was analyzed in elasto-plastic deformation ranges using finite element method. The impact bending moments were applied to the loading side adherend of the joint by dropping a weight. The name of FEM code employed was DYNA3D. The effects of Young’s modulus of the adhesive and the effect of the adhesive thickness on the stress variations at the interfaces were examined. In addition, the characteristics of joints subjected to the impact bending moments were compared with those of the joints under static bending moments, and the strength of the joints under impact bending moments was estimated by using the interface stress distributions. As the results, it was found that (1) the maximum value of the maximum principal stress σ1 occurred at the outside edges of the fixed side adhesive interface under the impact bending moments; (2) The maximum value of maximum principal stress σ1 increased as Young’s modulus of the adhesive increased when the joints were subjected to impact bending moments; (3) The maximum value of σ1 increased as the adhesive thickness decreased; (4) the characteristics of joints subjected to the impact bending moments were opposed to those subjected to the static bending moments. In addition, experiments were carried out to measure the strain response of butt adhesive joints subjected to impact bending moments using strain gauges, and the joint strengths were also measured. The measured strain response was compared with the numerical results. A fairly good agreement was found between the numerical and the measured results concerning the strain responses.© 2003 ASME