Bolted Flange Connections Research Articles

Determination of Bolt Forces for the Operational State of a Bolted Flange Connection / Wyznaczanie sił w śrubach w kołnierzowym połączeniu śrubowym w stanie eksploatacyjnym

In the paper modelling and calculations of an asymmetrical bolted flange connection at the operational stage are presented. The physical model of the joint is based on a flexible flange element that is connected with a rigid support by means of hybrid elements, which substitute bolts. Between the flange element and the support, the nonlinear Winkler model of a contact layer is taken into consideration. A computational model of the system is proposed, which makes it possible to analyze any preloaded bolted flange connection subjected to an eccentric normal load. Results obtained from the calculations are compared with experimental research described in [1].

OS1408 リングジョイントガスケット付き管フランジ締結体のFEM応力解析及び密封性能評価 : ボルト初期締付け力のばらつきの影響

OS1408 リングジョイントガスケット付き管フランジ締結体のFEM応力解析及び密封性能評価 : ボルト初期締付け力のばらつきの影響

Design of floating type bolted flange connections with grp flanges

The goal of the presented work is to enable plant operators in the chemical industry to design and to operate glass-reinforced-plastics (specified in the following as grp) piping with grp flanges at temperatures up to 80 °C, using polytetraflourethylene (PTFE) gaskets that shall replace the mandatory rubber gaskets. Various gaskets on the basis of rubber (EPDM) and PTFE were investigated in view of the boundary conditions in bolted flange connections with glass-fiber reinforced plastic flanges in compliance with DIN EN 13555. The rubber gasket and the PTFE based gasket with a PTFE-diffusion barrier meet the leakage rate criterion of TA Luft under the conditions of bolted flange connections with grp flanges. The mechanical behavior of bolted flange connections DN50 with grp flanges was investigated and is taken into consideration in a new calculation procedure, that accounts for the specific material properties of grp and thus allows higher bolt forces, what leads to increased tightness and operational reliability of the plants. This draft procedure with experimental pre-tests (already demanded in DIN 16966) is now available to design bolted flange connections with grp flanges.

Contact Model of Sealing Surfaces for Flange and Metallic Gasket Based on Fractal Theory

Metallic gasket seals are widely used in pressure vessels and piping. The failure of sealing systems is mostly caused not by the strength of flanges or bolts but by the leakage of the connections. The contact area of sealing surface has a major influence on the leakage of the bolted flange connections. The contact model of sealing surfaces of the flange and the metallic gasket was established on the basis of the modified M-B model, and the relationship between the contact area and the compressive stress is obtained. It’s found that the bigger the compressive stress, the bigger the contact area. When the compressive stresses are identical, the bigger fractal dimension and the less scale coefficient, the bigger the contact area. These can be used in the evaluation of sealing behavior of metallic gaskets.

A Yield Line Component Method for Bolted Flange Connections

Bolted connections are often used in steel structures to transfer of tension loads into wide flange members. The strength of these connections is determined with a prying action design procedure (outlined in the 13th edition AISC Steel Construction Manual) that checks the limit states of bolt tension rupture and bending of the flange. This procedure is valid only for fittings with limited bolt spacing and limited edge distance. This paper discusses a method to determine the local flange bending strength of a wide flange member using the yield line method. The proposed design method includes the effect of prying action on the bolts, and can be applied to many different connection configurations, including connections with large bolt spacing and edge distances and connections with web stiffeners. Comparisons with test data from 10 independent research projects will be used to verify the accuracy of the proposed method.

Stress Analysis and Sealing Performance Evaluation in Rectangular Box-Shape Bolted Flange Connection With Gasket Subjected to Internal Pressure

The contact gasket stress distributions in a rectangular box-shape bolted flange connection with a compressed sheet gasket subjected to internal pressure were analyzed using the finite element method. Leakage tests were also conducted for an actual rectangular box-shape bolted flange connection with a compressed sheet gasket under internal pressure. Using the obtained 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 from the Pressure Vessel Research Council (PVRC) procedure was substantial. In addition, a method to determine the bolt preload for a given tightness parameter was demonstrated and the difference in the determined bolt preload was shown between the present study and the PVRC procedure. The characteristics of the rectangular box-shape bolted flange connection were demonstrated by comparing those of circular bolted flange connections.

659 リングジョイントガスケット付き管フランジ締結体の密封性能評価及びFEM応力解析(フランジガスケット締結体の力学と密封性能評価IV)

659 リングジョイントガスケット付き管フランジ締結体の密封性能評価及びFEM応力解析(フランジガスケット締結体の力学と密封性能評価IV)

Finite Element Analysis of Behavior of Bolted Flange Connections under Bending Loading

Only a limited number of experimental and analysis reports exist concerning bolted flange connections under bending loading. In order to investigate the complex nonlinear phenomena, three dimensional elasto-plastic finite element analyses are performed. In those analyses, frictional contact model with small sliding option is applied between contacting pair surfaces of all connecting elements. Bolt pretension force is introduced in the initial step of analysis. From this study, the following results are obtainted:1) proposed finite element analysis method can be applicable to estimate complex nonlinear behavior of bolted flange type connections; 2) There is a sharp change in bending stiffness during loading, and lateral slip between two jointed flanges cause the bolt to carry shear load. The design of bolted joints should consider the interaction among cylinders, flanges and bolts.

802 繰返し曲げモーメントを受けるフランジ締結体のボルトのゆるみ(OS8-1 フランジガスケット締結体の力学と密封性能評価)

Bolted flange connections for wind power generations and chemical plants are subjected to repeated bending moments due to wind and earthquake loads. It is knou empirically that the bolt loosening in the bolted connections occur. Thus, it is necessary to examine the cause of the bolt loosening in the bolted flange connections under repeated bending moments. The objective of the present paper is to clarify the mechanism of bolt loosening in bolted flange connections subjected to repeated bending moments and to discuss on a solution for preventing the loosening of the bolted flange connections subjected to repeated bending moments, too. The loosening mechanism of the bolted flange connections is examined using the FEM calculations and the experiments. In the loosening experiments using the specified hexagon nuts, it is observed that the loosening of the bolts in the connection occurs due to the permanent-set of the bolts and the movement of the bearing surfaces in the flange due to the external repeated bending moment. In the FEM calculation, it is examined that the bolt loosening in the bolted flange connections qualitatively. In addition, it is found that as the bolt preload increases, the bolt loosening decreases. From the REM results and the experimental results, it is found that the most effective part for preventing the loosening of the bolted flange connection is the ecceninc nut.

高温度下での内圧を受ける非石綿ガスケット付き箱型圧力容器締結体の有限要素応力解析と密封性能評価

高温度下での内圧を受ける非石綿ガスケット付き箱型圧力容器締結体の有限要素応力解析と密封性能評価

605 管フランジ締結体の長期応力緩和特性の予測 : 3次元粘弾性特性の評価(フランジガスケット締結体の力学と密封性能評価II)

605 管フランジ締結体の長期応力緩和特性の予測 : 3次元粘弾性特性の評価(フランジガスケット締結体の力学と密封性能評価II)

606 管フランジ締結体の長期応力緩和特性の予測 : 延伸PTFEガスケットを用いた場合の漏洩量評価(フランジガスケット締結体の力学と密封性能評価II)

606 管フランジ締結体の長期応力緩和特性の予測 : 延伸PTFEガスケットを用いた場合の漏洩量評価(フランジガスケット締結体の力学と密封性能評価II)

On the Effect of External Bending Loads in Bolted Flange Joints

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 Pressure Vessel Research Council (PVRC) gasket constants Gb, a, and Gs, obtained from room temperature tightness (ROTT) tests. The analytical results including leakage predictions are validated by comparison to those obtained numerically by finite element analysis and experimentally on different size flanges. The overconservatism of the equivalent pressure is demonstrated.

OS0511 内圧を受ける大口径フランジ締結体のFEM解析および漏洩評価 : ボルトのばらつきの影響(OS05-03 フランジ締結体の密封性能評価,OS05 フランジガスケット締結体の力学と密封性能評価)

本研究では,内圧を受ける20インチフランジ締結体のボルト初期締め付け力のばらつきの影響について調べた.ガスケットの応力-ひずみ曲線のヒステリシスおよび非線形性を考慮した有限要素解析法によりガスケット接触応力分布を算出し,実際に実験を行うことでトルク管理法におけるボルト初期締め付け力のばらつきとその影響による漏洩量を測定し,両者の結果を比較検討した.その結果,ボルト軸力管理法に比べてトルク管理法(ASME法,HPIS法)ではいずれもボルト軸力がばらつき,目標ボルト締め付け力に達しないことが示された.

502 管フランジ締結体の応力解析と設計計算式の妥当性(フランジガスケット締結体の力学と密封性能評価I)

502 管フランジ締結体の応力解析と設計計算式の妥当性(フランジガスケット締結体の力学と密封性能評価I)

FEM Stress Analysis and an Evaluation of the Sealing Performance in Non-circular Box-shape Bolted Flange Connections with Gaskets Subjected to Internal Pressure

The contact gasket stress distribution of a non-circular box-shape flange connection with a compressed sheet gasket subjected to internal pressure was analyzed taking account a hysteresis of the gasket using finite element method (FEM). Leakage tests were also conducted using an actual non-circular box-shape flange connection with a compressed sheet gasket under internal pressure. By 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 was substantial between the values obtained from the present study and those from the PVRC procedure. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated. It was found that a higher bolt preload was needed for a given tightness parameter in the more safety design of box-shape flange connections.

501 内圧を受けるガスケット付き非円形箱型容器締結体の有限要素応力解析(フランジガスケット締結体の力学と密封性能評価I)

501 内圧を受けるガスケット付き非円形箱型容器締結体の有限要素応力解析(フランジガスケット締結体の力学と密封性能評価I)

201 内圧作用下でのガスケット付ボルト・フランジ締結体の応力解析 : ボルト軸力のばらつきの影響(材料力学I)

201 内圧作用下でのガスケット付ボルト・フランジ締結体の応力解析 : ボルト軸力のばらつきの影響(材料力学I)

Creep analysis of bolted flange joints

In the petrochemical and nuclear industries, the difficulty in assessing the effect of creep on the tightening load of bolted flanged connections is recognized. Under high temperatures, the leak tightness of bolted joints is compromised due to the loss of the bolt load as a result of creep of not only the gasket and bolt materials but also the flange material. Apart from acknowledgment of this effect, there exists no established design calculation procedure that accounts for creep. This is because the relaxation of the bolt load and the corresponding loss of the gasket contact stress are not easy to assess analytically. The main objective of the work is the development of a simple analytical solution to the creep-relaxation problem encountered in bolted flange connections of the float type. Particular emphasis is put towards relaxation caused by the flange and bolt material creep. The validation of the methodology is carefully checked against the more complex 3D numerical FE method using different size flanges. Based on the creep constants of the different joint elements (bolt, flange and gasket), the implemented analytical method is shown to predict the bolt and gasket load relaxation with reasonable accuracy. In some flange cases, up to 70% of bolt load relaxation is found with both methods depending on the flange creep material and size.

Three-dimensional transient sealing analysis of the bolted flange connections of reactor pressure vessel

The failure of sealing system of the bolt flange connections is the primary failure mode of the nuclear reactor pressure vessel (RPV). For the safety and integrity of RPV, it is important to predict the sealing behaviour of the bolt flange connections under various loading conditions. Based on the finite element (FE) method for coupled thermal elastoplastic contact problems, a three-dimensional (3D) transient sealing analysis program of nuclear reactor pressure vessels is developed with the consideration of the non-linearity from both surface and material, transient heat transfer and multiple coupled effects. A contact correction approach is proposed to simulate the loading of the bolt connection under the condition of pre-stressing. An automatic pre-processing program is developed for FE modelling of RPVs. Using these programs, a 1:4 scaled model of a 300 MW RPV is analyzed under the loading conditions including pre-stressing, pressurization, heating and cooling. The computational results obtained are in a good agreement with the data of experimental tests. These programs are also successfully used in analyzing the full-scale model of the RPV in a nuclear power plant.