An Estimation of Long-Term Sealing Performance for Bolted Pipe Flange Connections With Spiral Wound Gaskets Under Elevated Temperature

2020 ◽  
Author(s):  
Koji Sato ◽  
Toshiyuki Sawa
Keyword(s):  
Elevated Temperature ◽  
Heat Conduction Problem ◽  
Estimation Method ◽  
Transient State ◽  
Sealing Performance ◽  
Nominal Size ◽  
Calculation Results ◽  
Flexible Graphite ◽  
Spiral Wound

Abstract SWGs (Spiral Wound Gaskets) are well known as a most used gasket type in bolted pipe flange connections all over the world. Recently, the connections with SWGs have been used under more severe conditions such as higher temperature and pressure, and in addition, the connections have been used in the more long-term application. Thus, it is necessary for plant owners (gasket users) to know the long-term characteristics of the connections with SWGs from a standpoint of integrity in the connections. In this study, the objective is to establish a long-term estimation method of sealing performance for bolted pipe flange connections with SWGs under elevated temperature. The long-term characteristics of pipe flange connections with SWGs are estimated using FEM calculations in which the fundamental mechanical characteristics of SWGs such as compression property under changed temperature is considered, thermal expansion behavior, creep relaxation and sealing performance are taken into considerations. For verification of FEM calculations, the experiments are carried out for the pipe flange connections with SWGs of which the nominal size is ASME class 300 2inch under elevated temperature and internal pressure. The gasket used is chosen as SWG with flexible graphite filler. The change in axial bolt forces and an amount of leakage are measured and the measured results are fairly coincided with the FEM calculation results. In addition, the contact gasket stress in the connection with SWG is shown in 72 months. The FEM calculations are performed as heat conduction problem in transient state.

Sealing Performance Evaluation of Pipe Flange Connection With Spiral Wound Gasket Under Cyclic Thermal Condition

2009 ◽  
Author(s):  
Yoshio Takagi ◽  
Hiroyasu Torii ◽  
Toshiyuki Sawa ◽  
Yuya Omiya
Keyword(s):  
Thermal Expansion ◽  
Elevated Temperature ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Compression Tests ◽  
Flange Connection ◽  
Leakage Test ◽  
Sealing Performance ◽  
Spiral Wound

Although a lot of pipe flange connections are exposed to elevated temperature during long-term plant operation, a sealing performance of the pipe flange connections at elevated temperature is not well understood because of the experimental difficulty and the analytical problems which result from the lack of the materials properties of gaskets at elevated temperature. The authors have been evaluating the effects of the material properties of spiral wound gaskets (SWG) and the sealing performance of the pipe flange connections at elevated temperature with numerical and experimental analysis. The gasket stress induced by the mismatch of the thermal expansion between the gasket and flange/bolt increased as increasing the temperature in the case that the thermal expansion coefficient of the gasket was larger than that of bolt/flange material and the sealing performance of the pipe flange connection was improved. However, the thermal expansion coefficient declines at temperatures higher than 210 °C. In addition, the binder compositions of SWG vaporize and the mechanical properties slightly change at high temperature such as higher than 200°C. Therefore, the sealing performance of pipe flange connection with SWG might decline more than 200°C. The sealing performance and long-term durability of pipe flange connection with SWG at elevated temperature were evaluated in this study. The long term leakage test with heat cycle revealed that the sealing performance of pipe flange connection didn’t show any degradation for 21 days. The compression tests for the new, the thermal aged and the used gaskets were done to investigate the effect of material characteristics on the long term sealing performance. In addition to the leakage test and the compression tests, the thermal characteristics of SWG were evaluated by the Thermogravimetry/Differential Thermal Analyzer (TG/DTA) measurement. The measurement showed the weight loss of SWG more than 130°C. According to those experimental results and FE analysis, the effect of temperature on the sealing performance was discussed.

Effects of Post-Tightening on the Residual Bolt Force and the Sealing Performance of Flanged Connections With PTFE Gaskets (Long Term Effects at Room Temperature)

2011 ◽  
Author(s):  
Taiki Hagiri ◽  
Takashi Kobayashi ◽  
Kengou Nishiura ◽  
Kazuaki Uchiyama
Keyword(s):  
Room Temperature ◽  
Test Results ◽  
Long Term Effects ◽  
Viscoelastic Characteristic ◽  
Sealing Performance ◽  
Nominal Size ◽  
Gasket Material

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after a while to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is the main cause for the phenomenon. However, the long term effects of the post-tightening on the residual bolt forces and the sealing performance of flanged connections have not been clarified yet. In this study, two sets of flanged connections (2 inch in nominal size), in which PTFE gaskets were used, were prepared and tightened. One of the flanges was post-tightened after a designated time. The reduction of bolt forces and the change in the sealing performance were measured for about two months. The results were compared with those of flanges without post-tightening. Based on the test results, the effectiveness of post-tightening was discussed from the viewpoint of the residual bolt force and the sealing performance. It has been clarified that the effectiveness of post-tightening depends on gasket material and that post-tightening is effective for expanded PTFE gaskets.

Visco-Elastic FEM Stress Analysis of Bolted Flange Connections With PTFE-Blended Gaskets Under Elevated Temperature

2012 ◽  
Author(s):  
Koji Sato ◽  
Shinya Kurokawa ◽  
Toshiyuki Sawa
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Fluid Temperature ◽  
Long Term Conditions ◽  
Bolt Preload ◽  
Sealing Performance ◽  
Strain Relationship ◽  
Bolted Flange ◽  
Relationship Of

Bolted flange connections with gaskets have been used under high temperature and long-term conditions. Sometimes leakage accidents occur from the gasket interfaces due to the creep and relaxation phenomena. In the present paper, the changes of the gasket stress in bolted flange connections under high temperature conditions for a long-term are analyzed using FEM calculations taking into account the gasket temperature dependency. The gaskets used are PTFE-blended (V#GF300). It’s shown that the effect of the temperature on the stress-strain relationship of the gasket is substantial. The changes in the gasket stress of the connections for 12 months are analyzed using the FEM. The effects of nominal diameter of flanges, retightening and the fluid temperature (20 to 300 °C) on the change of gasket stress in the connections under elevated temperature are examined using the FEM calculations. It is found that the reduction in the gasket stress is over 40%. In addition, experiments to measure the axial bolt force were carried out. The calculated results are in a fairly good agreement with the experimental results. The results reveal that the long-term behavior of the bolted flange connections can be estimated in our study. Discussion is made on the effects of the bolt preload and retightening on the reduction of the gasket stress and the sealing performance.

Analysis of the Compression Behavior of Spiral Wound Gaskets

2009 ◽  
Author(s):  
A. Fitzgerald Jerry Waterland ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Pressure Vessel ◽  
Compression Behavior ◽  
Sealing Performance ◽  
And Performance ◽  
Flexible Graphite ◽  
Spiral Wound

Recent updates to the ASME B16.20 standard for spiral wound gaskets now require inner rings on all flexible graphite and PTFE filler spiral wound gaskets [1]. This new requirement is intended to prevent the occurrence of inward buckling; however the addition of an inner ring can have significant impact on the spiral wound gasket compression behavior and possibly its sealing performance. This paper explores the compression behavior and sealing performance of spiral wound gaskets, with and without inner rings, and thus provides a better understanding of their performance capabilities in ASME B16.5 flanges, as well as their design and performance within ASME Boiler & Pressure Vessel Code Appendix 2 flanges [2].

Effect of Aging Time on Sealing Performance of Non-Asbestos Gasket at Elevated Temperature

2004 ◽  
Author(s):  
Hirokazu Tsuji ◽  
Hirokazu Kitagawa ◽  
Noriyoshi Kodaira
Keyword(s):  
Elevated Temperature ◽  
Aging Time ◽  
Temperature Fluctuation ◽  
Stress Strain ◽  
Mixed Condition ◽  
Testing Apparatus ◽  
Sealing Performance ◽  
Conventional Tests ◽  
The Difference ◽  
Spiral Wound

Tests were concluded by a testing apparatus for ROTT/HOTT, which could continuously control the gasket temperature up to 450°C, under either the stress controlled condition or the strain controlled condition, while the conventional tests were conducted under the stress/strain mixed condition with the temperature fluctuation. The sealing performance of asbestos and non-asbestos gaskets was examined. For the non-asbestos SWG (Spiral wound gaskets) tested by the HOTT, the values of Tp at temperature 210°C and 300°C are distributed over 103∼104, while the value of Tp at 420°C is shifted to the relatively lower level of 102∼103. The non-asbestos SWG has same sealing performance as the substitute for the asbestos SWG between 210°C∼420°C. The PHOTT (Preheated Hot Operational Tightness Test, proposed in this study) is also carried out to compare the evaluation of sealing performance at 300°C with that at 210°C. The difference of sealing performance between the HOTT and the PHOTT at 300°C appears. The PHOTT is unavailable as a simplified substitutive test for the HOTT.

Evaluation of Sealing Behavior of Gaskets at Elevated Temperature Based on the Test Method HPIS Z105 Proposed in Japan

2009 ◽  
Author(s):  
Hirokazu Tsuji ◽  
Takashi Honda ◽  
Atsushi Yamaguchi ◽  
Takashi Kobayashi ◽  
Toshiyuki Sawa
Keyword(s):  
Elevated Temperature ◽  
Temperature Stress ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Testing Procedure ◽  
Test Method ◽  
Post Exposure ◽  
Sealing Performance ◽  
Stress Cycling ◽  
Spiral Wound

A method to test the sealing performance of gaskets at elevated-temperatures, HPIS Z105, will be published soon in Japan. This paper discusses the gasket testing procedure to obtain the sealing behavior of gasket at elevated-temperatures. This testing procedure extends the room-temperature gasket testing procedure HPIS Z104 to the elevated-temperatures. The purpose of this testing procedure is to evaluate the effect of a moderate exposure at the elevated-temperature on the sealing performance of the non-asbestos gasket. This testing procedure consists of 4 parts; pre-exposure room-temperature tightness test, aging exposure of gasket at elevated-temperature, stress cycling disturbances, and post-exposure room-temperature tightness test. In order to demonstrate the validity of the testing procedure, measurements of leak rates of several types of sheet gaskets and spiral wound gaskets are carried out. It has shown that the sealing behavior can be well characterized using the proposed testing procedure.

Sealing Performance Evaluation of Pipe Flange Connection Under Elevated Temperatures

2007 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Yoshio Takagi ◽  
Hiroyasu Torii
Keyword(s):  
Elevated Temperature ◽  
Stress Distribution ◽  
Internal Pressure ◽  
Elevated Temperatures ◽  
Flange Connection ◽  
Gas Leakage ◽  
Sealing Performance ◽  
Nominal Size ◽  
Operational Temperature ◽  
Contact Stress Distribution

Since a lot of pipe flange connections are exposed to elevated temperature during operation, it is important to evaluate the sealing performance of the connections under operational temperature. In this study, the sealing performance of pipe flange connection was experimentally evaluated by measuring the amount of gas leakage at room temperature (RT), 100 °C and 200 °C in addition to internal pressure. Non-asbestos graphite gaskets were used in the experiment. The nominal size of the pipe flange used during the experimental study was 3 inch. The eight bolts and nuts were tightened according to ASME PCC-1 and the Japanese method (HPIS). During assembly, the axial bolt force was individually measured with strain gauges attached to each bolt. The scatter in the axial bolt force during the assembling process was examined and compared between the ASME and the HPIS. In addition, the gasket contact stress distribution of each assembly process was calculated by finite element method under elevated temperature and internal pressure. In the FE study, experimentally measured physical properties such as elastic modulus and thermal expansion were used. ηhe amount of leakage was estimated from the contact gasket stress distribution obtained by FE analysis. The estimated axial bolt forces were compared with those of experimental ones.

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

2004 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Wataru Maezaki
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Performance Evaluation ◽  
Thermal Stress ◽  
Elevated Temperature ◽  
Stress Distributions ◽  
The Finite Element Method ◽  
Sealing Performance ◽  
Effects Of Temperature ◽  
Spiral Wound

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.

Effect of Material Properties of Gasket on the Sealing Performance of Pipe Flange Connections at Elevated Temperature

2015 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Yoshio Takagi ◽  
Hiroyasu Torii
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Elevated Temperature ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Material Properties ◽  
Compression Tests ◽  
Flange Connection ◽  
Sealing Performance ◽  
Spiral Wound

The sealing performance of the pipe flange connection depends on the compressive gasket stress. Therefore, the unexpected leakage can be avoided by estimating the change in compressive gasket stress during operation. In order to make such estimation, the material properties of the gasket are required as well as those of bolt and flange material. When the pipe flange connection is used under heated condition, the thermal expansion coefficient shows an important role. For example, if the thermal expansion coefficient of gasket is larger than that of pipe flange material, the gasket stress is expected to be increased by increasing the temperature and the sealing performance of pipe flange connection is improved. However, a gasket tends to be softening at high temperature. Beside, the creep phenomenon of gasket induces the decrease of gasket stress. Thus, the behavior of the gasket is complicated and it should be investigated to make a reliable design. In this paper, the high temperature properties, including thermal expansion and stress relaxation property of spiral wound gasket with expanded graphite are examined by compression tests at elevated temperature. The stress analysis with high temperature material properties obtained from the compression tests also conducted to estimate the sealing performance of pipe flange connection. As a result, the pipe flange connection with spiral wound gasket is expected to keep the superior sealing performance at 300 C for long time.

FEM Stress Analysis of Long-Term Sealing Performance for Bolted Pipe Flange Connections With PTFE Blended Gaskets Under Elevated Temperature

2016 ◽  
Author(s):  
Koji Sato ◽  
Toshiyuki Sawa ◽  
Takashi Kobayashi
Keyword(s):  
Elevated Temperature ◽  
Internal Pressure ◽  
Leak Rate ◽  
Load Factor ◽  
Stress Distributions ◽  
Sealing Performance ◽  
Basic Characteristics ◽  
The Relationship ◽  
Rigid Platen

Mechanical characteristics of bolted pipe flange connections with PTFE blended gaskets under elevated temperature are examined using FEM calculations and experiments. Firstly, the basic characteristics of the PTFE blended gaskets are measured such as the stress-strain curves, the thermal expansion coefficient and the relationship between the contact gasket stress and the leak rate at room temperature and some high temperature. The leak rates of the gasket at the averaged gasket stress are measured using the rigid platen. In addition, the creep characteristics of the gaskets are measured using the rigid platen under elevated temperature. Then, using the gasket basic characteristics measured above, the FEM calculations are carried out to analyze the mechanical characteristics such as 1) changes in axial bolt forces (the load factor), 2) the contact gasket stress distributions, 3) flange hub stress. Then, the sealing performance of bolted pipe flange connections is predicted using the contact gasket stress distributions obtained from the FEM calculations and the relationship between the gasket stress and the leak rate. In the FEM calculations, the value of the load factor due to the internal pressure is obtained as φg = 0.12. Furthermore, the sealing performance in long-term is estimated using the change in the axial bolt forces (creep) and the contact gasket stress distributions under heat cycle and internal pressure. For verification of the FEM calculations, the experiments were performed to measure the load factor (change in axial bolt forces), the leak rate of the connection at each temperature, and the hub stress. The FEM results are in a fairly good agreement with the measured results. In addition, the reduction in the contact gasket stress due to the heat cycle, internal pressure and the creep is demonstrated and the effect of the nominal diameter of pipe flanges on the sealing performance is shown.

Sign in / Sign up

Export Citation Format

Share Document