artigo v - comparação entre tipos de juntas.pdf

11
 Comparative study of the behaviour of conventional gasketed and compact non-gasketed anged pipe joints under bolt up and operating conditions M. Abid a, * , D.H. Nash b a Faculty of Mechanical Engineering, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology, Topi-23460, NWFP, Pakistan b  Departme nt of Mechanical Engineering, University of Strathclyd e, Glasgow, UK Received 11 November 2002; revised 11 October 2003; accepted 10 November 2003 Abstract Bolted anged joints comprise an assembly of a number of important individual components, which are required to perform well together in service. The ideal requirement for a bolted ange joint is a ‘zero-leak’ condition. However, whilst recommended design procedures for bolted ange joints are available in international codes and standards, leakage problems are still faced by industry. These are common in both normal operating (internal pressure loading) and critical event conditions. The drive is, therefore, to nd a ange joint assembly, which provides ‘zero-leak condition’ and requires little or no maintenance and handling. Considerable investigation in the area of optimised bolted  joints has been in progress for the past 10 years comparing traditional gasketed joints and ‘compact non-gasketed’ joints, using both analytical and experimental approaches. In this present study, two-dimensional non-linear nite element studies have been performed for bot h gas ket ed and non-ga ske ted bolte d an ge pipe joi nts. Bas ed on the stres s res ult s for the an ge and the bol t and the an ge rotation/displacement, compact non-gasketed ange joints are shown to be a viable and preferable alternative to the conventional gasketed ange joints. Recommendations are made for a best-t ange model for static load conditions with ‘zero-leak’ sealing in a ange joint. q 2004 Elsevier Ltd. All rights reserved. Keywords: Gasketed; Non-gasketed; Leakage; Flange joints; Finite element 1. Introduction All modern international desig n codes and stan dards provide calculation rules for the design of the anges, which are principally based on the Taylor–Forge method  [1,2]. Flang e joint s desi gned in accordance with international codes such as ASME  [3] , PD [4] , and CEN [5]  experience leakage and this problem is continuously faced by industry. In the present study, detailed analysis of ange joints is undertaken in order to observe the actual stress behaviour in ange, bolts and gasket. The reason for such a study is that a bolted ange joint is a combination of different elements which are inter-linked with each other to perform as a unit for ‘zero-leak’ condi tion. Math emati cally , the ‘zer o-leak condition is taken to be zero ange displacement of the ange at the inside diameter of the mating anges in the ange joint. In conventional ange analysis, no consider- ation has been given to this important issue, i.e. the anges, bol ts and gas ket are dis cussed and are tre ate d ent ire ly separa tel y. The ref ore, wit h the ava ila bil ity of modern analysis tools, it is possible to adopt a ‘design-by-analysis’ app roa ch for the bol ted ange joi nt in order to pro vid e accurate values for the stresses in key areas as required; for example, at hub-ange llets, in the bolts and in the gasket element itself. In addition for conventionally designed anges, where the re is a mea sur e of inc ons ist enc y of the dimens ion s between ange sizes, it has been difcult to standardise on a sin gle pro ced ure to ove rco me the str ess and deect ion desig n versus leaka ge prob lem. Therefor e, by means of comparison to the conventional ange design, a new novel ange design is also studied which is dimensionally very compact, is light weight and is without a gasket. This is designated the ‘non-gasketed’ bolted joint. Stresses in the ange ring, bolts and gasket, various displacements and bolt bending results are studied for both the gasketed and non- gasketed ange joints. Previous work by Power  [6]  used a full three-d imen- sional (3D) non-line ar analy sis for compa rativ e stud y of 0308-0161/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpvp.2003.11.013 International Journal of Pressure Vessels and Piping 80 (2003) 831–841 www.elsevier.com/locate/ijpvp *  Correspondin g author. Tel.:  þ 92-938-71858~61; fax:  þ92-938-71889. E-mail address:  [email protected] (M. Abid).

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  • Comparative study of the behaviour of conventional gasketed and compact

    non-gasketed flanged pipe joints under bolt up and operating conditions

    M. Abida,*, D.H. Nashb

    aFaculty of Mechanical Engineering, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology, Topi-23460, NWFP, PakistanbDepartment of Mechanical Engineering, University of Strathclyde, Glasgow, UK

    Received 11 November 2002; revised 11 October 2003; accepted 10 November 2003

    Abstract

    Bolted flanged joints comprise an assembly of a number of important individual components, which are required to perform well together

    in service. The ideal requirement for a bolted flange joint is a zero-leak condition. However, whilst recommended design procedures for

    bolted flange joints are available in international codes and standards, leakage problems are still faced by industry. These are common in both

    normal operating (internal pressure loading) and critical event conditions. The drive is, therefore, to find a flange joint assembly, which

    provides zero-leak condition and requires little or no maintenance and handling. Considerable investigation in the area of optimised bolted

    joints has been in progress for the past 10 years comparing traditional gasketed joints and compact non-gasketed joints, using both

    analytical and experimental approaches. In this present study, two-dimensional non-linear finite element studies have been performed for

    both gasketed and non-gasketed bolted flange pipe joints. Based on the stress results for the flange and the bolt and the flange

    rotation/displacement, compact non-gasketed flange joints are shown to be a viable and preferable alternative to the conventional gasketed

    flange joints. Recommendations are made for a best-fit flange model for static load conditions with zero-leak sealing in a flange joint.

    q 2004 Elsevier Ltd. All rights reserved.

    Keywords: Gasketed; Non-gasketed; Leakage; Flange joints; Finite element

    1. Introduction

    All modern international design codes and standards

    provide calculation rules for the design of the flanges, which

    are principally based on the TaylorForge method [1,2].

    Flange joints designed in accordance with international

    codes such as ASME [3], PD [4], and CEN [5] experience

    leakage and this problem is continuously faced by industry.

    In the present study, detailed analysis of flange joints is

    undertaken in order to observe the actual stress behaviour in

    flange, bolts and gasket. The reason for such a study is that a

    bolted flange joint is a combination of different elements

    which are inter-linked with each other to perform as a unit

    for zero-leak condition. Mathematically, the zero-leak

    condition is taken to be zero flange displacement of the

    flange at the inside diameter of the mating flanges in the

    flange joint. In conventional flange analysis, no consider-

    ation has been given to this important issue, i.e. the flanges,

    bolts and gasket are discussed and are treated entirely

    separately. Therefore, with the availability of modern

    analysis tools, it is possible to adopt a design-by-analysis

    approach for the bolted flange joint in order to provide

    accurate values for the stresses in key areas as required; for

    example, at hub-flange fillets, in the bolts and in the gasket

    element itself.

    In addition for conventionally designed flanges, where

    there is a measure of inconsistency of the dimensions

    between flange sizes, it has been difficult to standardise on a

    single procedure to overcome the stress and deflection

    design versus leakage problem. Therefore, by means of

    comparison to the conventional flange design, a new novel

    flange design is also studied which is dimensionally very

    compact, is light weight and is without a gasket. This is

    designated the non-gasketed bolted joint. Stresses in the

    flange ring, bolts and gasket, various displacements and bolt

    bending results are studied for both the gasketed and non-

    gasketed flange joints.

    Previous work by Power [6] used a full three-dimen-

    sional (3D) non-linear analysis for comparative study of

    0308-0161/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.ijpvp.2003.11.013

    International Journal of Pressure Vessels and Piping 80 (2003) 831841

    www.elsevier.com/locate/ijpvp

    * Corresponding author. Tel.: 92-938-71858~61; fax: 92-938-71889.E-mail address: [email protected] (M. Abid).

  • three different types of joints for the internal pressure

    loading case only. Using 3D modelling the variation of

    contact pressure and stress behaviour in the flange and the

    bolts was studied. The contact, or interface pressure was

    used as the main quantitative measure of the sealing ability

    of the three joint styles. More recently, Cao [7] also

    performed 3D FEA considering gasket non-linearity under

    both bolt up and operating conditions and studied the joint

    strength and sealing capability. Similarly, Fukuoka [8] has

    studied the bolt stress scatter, effect of tightening sequence,

    bearing surfaces and number of tightening passes. However,

    flanged pipe joints have already been modelled using 2D

    finite element analysis by Hyde et al. [9], Shoji [10] and by

    one of the present authors [11].

    In the present study, in order to compare the two flange

    styles and their relative performance, a flange size of 4 in.,

    900# class was selected. 2D axi-symmetric non-linear finite

    element analysis for both the joints was carried out for

    internal pressure loading only. During the analysis, the

    intention was not to study the variation in contact pressure

    and contact area but rather to study the stress behaviour in

    the flange and the bolts, especially the effect of bolt bending,

    bolt pre-load and flange displacement/rotation. It is noted

    that variation in contact pressure and contact area is

    theoretically of importance but any deformation on the

    flange surface, specifically for the metal-to-metal contact

    non-gasketed flange joint, cannot stop leakage even with a

    very high contact pressure. This has been noted during

    published experimental tests [11]. However, it is recognised

    that the contact pressure study is of course important from

    the design point of view, in order to take account of bolt

    behaviour and the contact force of the flanges, but will not

    be reported herein.

    2. Allowable stresses and flange joint configuration

    2.1. Allowable stresses

    The yield stress of the flange and pipe material selected

    was 372 N/mm2, giving a nominal design stress of

    248 N/mm2. High strength bolts of 30 and 10 mm were

    used in the gasketed and non-gasketed joints. Material

    properties for flange, pipe, bolts and gasket selected are

    given in Table 1.

    2.2. Flange geometry

    The configurations under examination and parameters

    used for modelling are shown in Fig. 1a and b for the

    gasketed and non-gasketed joints.

    Gasketed flange. For the flange and the gasket geometry,

    the dimensions were obtained from BS1560 [12]. A washer

    is not included in the present work, since for gasketed joints;

    it is not a mandatory requirement of the PD or ASME code.

    Gasket was modelled as a solid ring for the gasketed joint. In

    actual practice during the bolt up condition, it is necessary to

    compress the raised sealing part down to equal to

    Nomenclature

    A outside diameter of the flange

    B inside diameter of the flange

    C bolt circle diameter

    g0 wall thickness of basic shell/pipe

    h taper-hub length

    t non-gasketed flange thickness

    jh joint height

    pid pipe inside diameter

    pod pipe outside diameter

    wth pipe thickness

    sh shoulder height

    sod shoulder outside diameter

    hubht hub height

    hod hub outside diameter

    gth gasket thickness

    gid gasket inside diameter

    god gasket outside diameter

    gcringid gasket centring ring inside diameter

    gcringod gasket centring ring outside diameter

    gsrght gasket seal ring height

    bcd bolt circle diameter

    fod flange outside diameter

    bd bolt diameter

    bhd bolt head diameter

    bhh bolt head height

    f element contact stiffness factor

    Table 1

    Material properties of gasketed and non-gasketed flange joints

    Part Gasketed flange joint Non-gasketed flange joint

    E(N/mm2)

    y Design stress(N/mm2)

    As per code E(N/mm2)

    y Design Stress(N/mm2)

    As per code

    Flange and pipe 173,058 0.3 248.2 2=3sy ASTM A350 LF2 or A105 203,395 0.3 248.2 2=3sy ASTM A350 LF2 or A105Bolt 168,922 0.3 723.9 sy ASTM SA193 B7 204,000 0.3 640.0 sy ISO 898, Grade 8.8Gasket 164,095 0.3 206.8 2=3sy ASTM A182 F316

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841832

  • the centring ring thickness in order to energise the proper

    sealing capability of the gasket as recommended by the

    gasket suppliers. During the previous experimental studies

    [11], an inconsistency in the gasket outside diameter

    dimension were noted and the outside diameter of the

    gasket was subsequently machined to allow fit up into the

    flange joint. Flange parameters used are given in Table 2.

    Non-gasketed flange. A washer with the bolt is

    recommended for the non-gasketed joint but it was observed

    in preliminary studies that it does not have a significant

    effect on stress and deformation results for the axi-

    symmetric model. It was, therefore, decided not to include

    the washer in the analytical model. For the non-gasketed

    joint, to achieve better joint strength and sealing ability, a

    higher initial pre-load and a positive taper angle of 0.038

    on the flange surface is applied. Flange parameters used are

    given in Table 3.

    3. Finite element modelling

    Previous work by Spence et al. [13] and Nash et al. [14],

    showed the viability of a 2D axisymmetric model, for what

    is essentially a 3D component. In neglecting the holes in the

    flange and the presence of individual bolts round the flange,

    the system can be considered as a continuous bolt ring

    located at the bolt centre and running round the circumfer-

    ence of the bolt circle. Schematic quarter models of both

    flange joints are shown in Fig. 2a and b. The ANSYS finite

    element code v5.7 was employed throughout this work.

    Fig. 1. Parameters used in the finite element model of flange joints (a) gasketed, (b) non-gasketed.

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841 833

  • Fully parametric finite element models were used through-

    out so that the time involved in building the scaled geometry

    models of other different sizes is minimised.

    3.1. Element selection

    Since the flange, bolt and gasket stresses were the

    required outputs from this study, it was necessary to use two

    classes of element: solid element PLANE82 to model the

    solid entities and contact element CONTACT48 to measure

    contact pressure or stress variation between the mating

    surfaces. Contact stiffness (KN) for CONTACT48 element

    quantifies the level of penetration that the target surface

    allows. Over penetration results in inaccuracy if it is too

    small a value and non-convergence of solution results if it is

    too large a value. From the earlier study by Spence et al.

    [14], it is noted that only a lower value of f ; the element

    contact stiffness factor, affects the maximum axial stress at

    the intersection of the taper hub and the vessel. When

    varying the value of f between 0.1 and 100, at the value of

    f $ 1 stress was almost levelled out, and therefore, a valuewas selected of f 10 for further analysis. The effect of thevariation of contact stiffness on stress is shown in Fig. 3.

    3.2. Mesh refinement

    In order to ensure accurate results, a reasonably refined

    mesh was applied in the regions of interest such as at the

    hub-pipe and hub-flange intersections. The mesh for the

    gasketed flange was also refined at the flange shoulder to

    measure the contact stresses at the gasket. Twenty-one and

    seven elements across the pipe and hub thickness, 10 and 13

    elements across the flange thickness and 10 and 12 elements

    across the bolt width were defined for the gasketed and non-

    gasketed flange joints. Illustrations of the meshed models

    are shown in Fig. 4a and b.

    3.3. Boundary conditions

    The boundary conditions applied for both the joints are

    shown in Fig. 4. Internal pressure is applied at the inside

    diameter, and the loading due to the head is directly applied

    as nodal forces across the wall of the pipe which are

    obtained using the internal axial force Ppr2i divided by 2prt(i.e. Pr2i =2rt). The flanges are free to move in either theaxial or radial direction and rotate, providing the exact

    behaviour of the stresses in the flange and the bolt.

    Symmetry planes are constrained in both the axial and

    radial directions. For the gasketed joint, due to the gap

    between the flanges, internal pressure is also applied on

    the gasket inside diameter as well as on the flange shoulder

    in the gap. The gasket is constrained in the radial direction

    to prevent it moving radially since, in practice, it is located

    interior to the bolts. The bolts for both flanges are

    constrained at the mid diameter in the radial direction as

    Table 3

    Non-gasketed flange joints geometric parameters

    Flange hub

    length, h (mm)

    Pipe thickness,

    g0 (mm)

    Joint height,

    jh (mm)

    Bolt circle

    dia., C (mm)

    Flange outside

    dia., A (mm)

    Flange inside

    dia., B (mm)

    Flange thick.,

    t (mm)

    Flange surface

    angle, taper (deg)

    Bolt dia.,

    bd (mm)

    34 13.5 102.6 146 171 87.3 30 0.03 10

    Fig. 2. Schematic quarter models for (a) gasketed, (b) non-gasketed flange

    joints, showing bolts as continuous bolt ring (as used in axi-symmetric

    representation).

    Table 2

    Gasketed flange joints geometric parameters

    Flange parameters

    Flange hub length,

    hubht (mm)

    Flange joint

    height, jh (mm)

    Bolt circle dia.,

    bcd (mm)

    Flange outside

    dia., fod (mm)

    Flange inside

    dia., pid (mm)

    Flange thick.,

    fh (mm)

    Flange hub

    dia., hod (mm)

    Shoulder height,

    sh (mm)

    Shoulder outside

    dia., sod (mm)

    69.9 71.67 235 292 87.3 44.4 159 6.4 157.2

    Gasket, pipe and

    bolt parameters

    Gasket inside

    dia., gid (mm)

    Gasket outside

    dia., god (mm)

    Gasket thick.,

    gth (mm)

    Gasket seal

    ring inside dia.,

    gcringid (mm)

    Gasket seal

    ring outside dia.,

    gcringod (mm

    Pipe inside

    dia., pid (mm)

    Pipe outside dia.,

    pod (mm)

    Pipe thick.,

    wth (mm)

    Bolt dia.,

    bd (mm)

    120.65 149.35 4.5 106.43 206.50 87.3 114.3 13.5 30

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841834

  • they cannot move in this direction within the bolt hole. An

    axial displacement is applied on the bottom nodes of the bolt

    shank which was progressively optimised by sequential

    iteration, to obtain the required pre-stress.

    3.4. Initial bolt up and operating (internal pressure) loads

    A nominal pre-load of about 35% (245 N/mm2) of

    the yield stress of the bolt (723 N/mm2) was chosen for

    the gasketed joint as per the achieved maximum strain

    in the bolt at the applied torque of 505 N m during the

    experimental study [11]. The ASME code does not

    specify a magnitude of pre-load for the bolts, rather only

    a minimum seating stress that relates to the gasket style

    and composition. In addition, in general practice, the

    pre-load for the gasketed joint is based partially on the

    practical knowledge that most fitters of flanged joints

    manually tighten the bolts as hard as possible. For the

    non-gasketed joint a pre-load approximately 80% of the

    yield stress of the bolt [11] was applied for better joint

    strength due to the fact that the higher the pre-load the

    better the joint is and is easily achieved for metal-to-

    metal contact flanges due to no gasket stress limitation.

    As the yield strength of the bolt material is 640 N/mm2,

    so the applied bolt pre-stress is 512 N/mm2. This stress

    is based on the bolt shank area of 78.54 mm2, whereas

    the bolt strength is taken as per thread root area

    (58 mm2), resulting in pre-stress to be applied was

    378 N/mm2.

    After the bolt up, an internal pressure of 15.3 N/mm2

    was applied as per the pressure rating recommended for

    the flange size of 4 in., class 900# as defined by the

    codes. This applied pressure is the maximum permissible

    working pressure, whereas, in order to compare the stress

    pattern or structural integrity of both the flange joints,

    the pressure required was raised to the proof test pressure

    of 23 N/mm2 and thereafter to a maximum value of

    40 N/mm2 (i.e. 2.6 times the normal operating pressure

    of 15.3 N/mm2).

    4. Results and discussion

    4.1. Comparison of calculated and FEA results

    To verify the models, the main pipe wall axial and hoop

    stresses were compared with the calculated stress results and

    were found in good agreement.

    Fig. 3. Effect of contact stiffness on maximum axial stress (N/mm2).

    Fig. 4. Element plots for flange joints (a) gasketed, (b) non-gasketed with

    enlarged hub portion.

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841 835

  • 4.2. Comparison of results for both the joints

    4.2.1. Non-gasketed flange joint

    With reference to Fig. 5ac and Table 4, the following

    observations may be made. At the maximum allowable

    working pressure of 15.3 N/mm2, the maximum stress

    intensity in the flange is less than the allowable stress of

    the flange material. The stress is higher at the hub-flange

    fillet, than at the inside diameter at the hub. A high stress

    is also observed at the area under the bolt head, due to the

    high-applied pre-load in the bolt. The maximum principal

    stress is less than the allowable of the flange material even

    at a pressure of 2.6 times the maximum permissible

    working pressure. The contact stress variation between the

    two flanges is very small from the inside diameter (a

    value of 19 N/mm2) to the outside diameter (a value of

    35 N/mm2) with the applied internal pressure. The rotation

    from inside to outside diameter of the non-gasketed flange

    is almost negligible at the maximum permissible, the

    proof test and the maximum applied pressures, and is

    recorded in Table 4.

    4.2.2. Gasketed flange joint

    With reference to Figs. 6a,b and 7a,b and Table 4, the

    following observations were made. For the gasketed flange

    joint, even during pre-loading, stress intensity and principal

    stress is significantly more than the allowable of the flange

    material at the hub-flange fillet. The application of internal

    pressure added to this effect resulting in increase in stress.

    This indicates yielding at hub-flange fillet during both bolt

    up (pre-loading) and operating (pressure) loading (Fig. 6a

    and b). At other locations, i.e. hub-pipe and hub-centre, the

    resulting stress was less than the allowable.

    It is also important to note that the local yielding is more

    than 20% of the hub-flange fillet depth, Fig. 7a. The

    maximum stress at the inside diameter of the hub is also

    higher than the allowable of the flange material. In addition,

    a high stress is present at the edge of the shoulder, which

    acts as the pivot point due to the flange rotation. The higher

    stresses in this region are possibly due to the geometric

    stress concentration and idealised finite element modelling

    (Fig. 7a). From Fig. 7b and c stress intensity plots, overall

    stress variation in the flange and bolt is obvious. The rotation

    Fig. 5. Non-gasketed flange joint, (a) stress intensity plot for full joint at internal pressure of 15.3 N/mm2, (b) stress intensity plot for flange only at internal

    pressure of 15.3 N/mm2, (c) maximum principal stress plot at internal pressure of 40 N/mm2.

    Table 4

    Non-gasketed flange joint, maximum principal stress and flange rotation results

    Internal Pressure (N/mm2) Maximum principal stress (N/mm2) Flange rotation (degree)

    Gasketed flange joint (mm) Non-gasketed flange joint (mm) Gasketed flange joint (mm) Non-gasketed flange joint (mm)

    15.3 309.59 94.64 0.1589 0.0300

    23.0 316.62 100.31 0.3085 0.0307

    40.0 321.66 137.95 0.3131 0.0424

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841836

  • of the gasketed flange joint is proportional to the applied

    internal pressure. For the gasketed flange joint, flange

    rotation means the flange portion between

    the shoulder outside diameter and the flange outside

    diameter. Shoulder rotation means the rotation of the

    shoulder portion only.

    4.3. Bolt stress behaviour of joints

    4.3.1. Non-gasketed flange joint

    With reference to Fig. 8a,b and Table 5, the following

    may be concluded. There is high stress at the top of the bolt

    shaft close to the bolt head and the shank corner. However,

    Fig. 6. Gasketed flange joint, (a) principal stress plot after pre-loading or bolt up, (b) stress intensity (exaggerated) plot for flange at a pressure of 15.3 N/mm2.

    Fig. 7. Gasketed flange joint, (a) stress intensity plot showing the location and the depth at which the yielding starts at a pressure of 15.3 N/mm2, (b) stress

    intensity plot for full joint model, (c) stress intensity plot for flange only at internal pressure of 15.3 N/mm2.

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841 837

  • no yielding resulted and the maximum stress in the bolt is

    less than the allowable stress of the bolt material. From

    the stress variation in the bolt, the bolt bending is very

    small, due to the very small flange rotation with applied

    internal pressure.

    4.3.2. Gasketed flange joint

    With reference to Fig. 9a,b and Table 5, similar to the non-

    gasketed joint bolt, a high stress occurred at the corner of the

    bolt head and the bolt shank with no yielding. However, bolt

    bending is obvious for the gasketed joint due to a difference

    of stress of about 200 N/mm2 at the inside and outside nodes.

    This difference is a maximum of 40 N/mm2 for the non-

    gasketed joint, which is very small compared to the values

    obtained for the gasketed joint. This stress variation in the

    bolt shows the flange rotation during pre-loading (bolt up)

    and operating (pressure) loads.

    4.4. Contact stress behaviour for gasketed and non-gasketed

    joints

    Due to the flange rotation, the contact pressure on the

    gasket varies from the gasket inside to the outside diameter.

    The gasket was modelled as a solid ring. The deformed

    shape of the gasket is shown in Fig. 10 and the gasket

    contact stress variation is shown in Fig. 11. From the high

    stress at the seal ring outside diameter, the flange rotation is

    again obvious and shows that during the bolt-up, the seal

    ring can be damaged for any applied higher pre-load. As

    discussed earlier, it is important for the gasketed joint to

    achieve the proper seating stress recommended by the gasket

    Fig. 8. Non-gasketed flange joint bolt only, (a) stress intensity plot for the full joint due to the operating load, (b) stress variation in the bolt due to the operating

    load (zoomed bolt portion only).

    Table 5

    Bolt stress variation for non-gasketed and gasketed flange joints with the variation of pressure

    Internal pressure

    (N/mm2)

    Stress in bolts

    (N/mm2)

    Non-gasketed flange joint Gasketed flange joint

    Inside diameter

    (mm)

    Mid diameter

    (mm)

    Outside diameter

    (mm)

    Inside diameter

    (mm)

    Mid diameter

    (mm)

    Outside diameter

    (mm)

    15.3 392.20 374.13 356.06 343.65 242.87 141.86

    23.0 391.88 373.10 354.30 346.86 243.17 141.86

    40.0 402.26 376.38 350.46 347.50 243.82 139.93

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841838

  • supplier for the no leak condition. It is obvious from the

    gasket stress variation that a very low stress value is

    achieved on the contact area between the flange and the

    gasket. In addition, in axisymmetric modelling, the gasket is

    modelled as per the ideal required condition.

    In Fig. 12, the stress variation at the contact surface with

    the symmetry plane for the non-gasketed joint is shown

    which increased gradually from the inside to the outside

    diameter during the application of internal pressure.

    5. Conclusions

    In view of the stress distributions resulting in the flange

    and bolts together with the observed flange rotation, bolt

    bending, bolt fatigue and bolt relaxation it is concluded that

    a dynamic behaviour in the gasketed flange joint is present

    during both the bolt-up and operating conditions. This is

    primarily due to the inclusion of a flexible gasket element

    between the flanges leading to a continually varying

    situation where, when bolt or pressure load changes, the

    flange faces move and rotation results in response. This

    provides permanent damage in the flange and repeated use

    of this joint cannot ensure its performance for zero-leak,

    even though the joint may be well assembled. Secondly, due

    to limitations of the choice of gasket seating stress to avoid

    crushing, a higher initial stress cannot be applied in the

    bolts, and therefore, the available strength of the high yield

    bolts cannot be utilised.

    In comparison, stresses observed in the non-gasketed

    flanged joint are within the specified allowable levels even

    up to an internal pressure of 2.5 times design pressure.

    Fig. 9. Gasketed flange joint bolt only, (a) stress intensity plot for the full joint due to the operating load, (b) stress variation in the bolt due to the operating load

    (zoomed bolt portion only).

    Fig. 10. Gasketed flange joint, deformed gasket plot.

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841 839

  • Fig. 11. Gasketed flange joint, gasket stress variation plot along the gasket, after the operating load.

    Fig. 12. Non-gasketed flange joint, stress variation at the symmetry plane (contact surface).

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841840

  • A non-gasketed metal-to-metal contact joint without a

    separating gasket is concluded as having static mode of

    load due to no significant movement of the flange faces with

    a change in bolt or pressure load. Due to this no bolt bending

    and so no bolt fatigue results, therefore, it is considered a

    safe joint. Finally due to the compact dimensions, it is

    comparatively 10 times lighter than the conventional

    gasketed flange joint, resulting in easy handling and joint

    assembly.

    Hence, as a result of the detailed finite element study

    presented herein, compact non-gasketed flange joints may

    readily be considered as a viable alternative to the

    conventional gasketed flange joints presently in use.

    References

    [1] Waters EO, Taylor JH. The strength of pipe flanges. Trans Mech

    Engng 1927;49:53142.

    [2] Waters EO, Wesstrom DB, Rossheim DB, Williams FSG. Formulas

    for stresses in bolted flanged connections. Trans ASME 1937;59:

    1617.

    [3] American Society of Mechanical Engineers. ASME boiler and

    pressure vessel code. Section VIII, Division 1. App. Y, 2001 Edition.

    [4] PD5500:2000. Unfired fusion welded pressure vessels. British

    Standards Institution, London.

    [5] EN 13445. European unfired pressure vessels, CEN; 2002.

    [6] Power DJ. A study of conventional and unconventional flanged pipe

    joint styles using non linear finite element analysis techniques. MPhil

    Thesis; 1997.

    [7] Cao D, Xu H. 3-D finite element analysis of bolted flange joint

    considering gasket non-linearity. Pressure Vessel Piping Conf Boston

    1999;382:1216.

    [8] Fukuoka T, Takaki T. Evaluations of bolt-up sequence of pipe flange

    using three dimensional finite element analysis. Pressure Vessel

    Piping Conf Boston 1999;382:2135.

    [9] Hyde TH, Lewis LV, Fessler H. Bolting and loss of contact between

    cylindrical flat-flanged joints without gaskets. J Strain Anal 1988;23:

    18.

    [10] Shoji Y, Nagata S. A new analysis method for flange-gasket systems.

    ASME Pressure Vessel Piping Conf Boston 1999;382:11320.

    [11] Abid M. Experimental and analytical studies of conventional

    (gasketed) and unconventional (non gasketed) flanged pipe

    joints (with special emphasis on the engineering of joint strength

    and sealing). PhD Thesis. University of Strathclyde, Glasgow;

    2000.

    [12] British Standard BS1560: Section 3.1. Circular flanges for pipes,

    valves and fittings. BSI London; 1989.

    [13] Spence J, Macfarlane DM, Tooth AS. Metal-to-metal full-face

    taper-hub flanges: finite element model evaluation and preliminary

    plastic analysis results. Proc Inst Mech Engrs 1998;212(Part E):

    5769.

    [14] Nash DH, Spence J, Tooth AS, Abid M, Power DJ. A parametric study

    of metal-to-metal full face taper-hub flanges. Int J Pressure Vessel

    Piping 2000;77:7917.

    M. Abid, D.H. Nash / International Journal of Pressure Vessels and Piping 80 (2003) 831841 841

    Comparative study of the behaviour of conventional gasketed and compact non-gasketed flanged pipe joints under bolt up and operIntroductionAllowable stresses and flange joint configurationAllowable stressesFlange geometry

    Finite element modellingElement selectionMesh refinementBoundary conditionsInitial bolt up and operating (internal pressure) loads

    Results and discussionComparison of calculated and FEA resultsComparison of results for both the jointsBolt stress behaviour of jointsContact stress behaviour for gasketed and non-gasketed joints

    ConclusionsReferences