# EN 1591-1:2001

(Main)## Flanges and their joints - Design rules for gasketed circular flange connections - Part 1: Calculation method

## Flanges and their joints - Design rules for gasketed circular flange connections - Part 1: Calculation method

1.1 General

This European Standard defines a Calculation method for bolted, gasketed, circular flange joints. Its purpose is to ensure structural integrity and control of leaktightness. ENV 1591-2 gives values for gasket properties which can be used in the Calculation method.

1.2 Requirement for use of the Calculation method

Where permitted, the Calculation method is an alternative to design validation by other means e.g.

special testing;

proven practice;

use of standard flanges within permitted conditions.

1.3 -Validity

1.3.1 Geometry

The Calculation method is applicable to the configurations having:

flanges whose section is given or may be assimilated to those given in Figures 4 to 12;

four or more identical bolts uniformly distributed;

gasket whose section and configuration after loading can be assimilated by one of those given in Figure 3;

flange dimension which meet the following conditions:

a) 0,2 bF/eF 5,0; 0,2 bL/eL 5,0

b)

e sub FUNC F ~>=~max ~LEFT LBRACE e sub 2;~ d sub { FUNC B0};~ p sub FUNC B ~ × ~ NROOT 3 {(0,01...0,10) ~ × ~ p sub FUNC B / b sub FUNC F } RIGHT RBRACE

c) cos s 1/(1 + 0,01 ds/es)

NOTE 1 For explanations of symbols see clause 3.

NOTE 2 The condition bF/eF 5,0 need not to be met for collar in combination with loose flange.

NOTE 3 The condition

is for limitation of non-uniformity of gasket pressure due to spacing of bolts. The values 0,01 and 0,10 are to be applied for soft (non-metallic) and hard (metallic) gaskets respectively. A more precise criterion is given in annex A.

NOTE 4 Attention may need to be given to the effects of tolerances and corrosion on dimensions; reference should be made to other codes under which the calculation is made, for example values are given in EN 13445 and EN 13480.

## Flansche und ihre Verbindungen - Regeln für die Auslegung von Flanschverbindungen mit runden Flanschen und Dichtung - Teil 1: Berechnungsmethode

Anwendungsbereich

1.1 Allgemeines

Diese Europäische Norm legt eine Berechnungsmethode für die Auslegung von Flanschverbindungen mit runden

Flanschen, Schrauben und Dichtung fest. Sie hat den Zweck, die Festigkeit der Konstruktion sicherzustellen und die

Dichtigkeit zu beherrschen. ENV 1591-2 legt Dichtungskennwerte fest, die in dieser Norm verwendet werden

können.

1.2 Erfordernis für die Anwendung dieser Berechnungsmethode

Dieses Verfahren bietet (soweit zugelassen) eine Alternative für die Bestätigung der Gültigkeit der Auslegung mit

anderen Mitteln, z. B.:

besondere Prüfung;

vorliegende Erfahrung;

Verwendung genormter Flansche unter zulässigen Bedingungen.

1.3 Gültigkeit

1.3.1 Geometrie

Dieses Verfahren ist anwendbar für Konfigurationen mit:

Flanschen, deren Querschnitt gleich ist oder zurückgeführt werden kann auf die in den Bildern 4 bis 12 angege-

benen Flansche;

vier oder mehr gleichen Schrauben, gleichmäßig verteilt;

Dichtung, deren Querschnitt und Einbaulage unter Belastung durch eine der Konstruktionen in Bild 3 dargestellt

werden kann;

Flanschmaßen, die folgende Bedingungen erfüllen:

a) 0,2 bF/eF 5,0; 0,2 bL/eL 5,0

b)

c) cos s 1/(1 + 0,01 ds/es)

ANMERKUNG 1 Bedeutung der Kurzzeichen siehe Abschnitt 3.

ANMERKUNG 2 Die Einschränkung bF /eF 5,0 braucht nicht eingehalten zu werden bei Bunden oder Bördeln in Verbindung mit

losen Flanschen.

ANMERKUNG 3 Die Bedingung dient der Begrenzung einer ungleichmäßigen Dichtungs-

pressung hervorgerufen durch die Abstände zwischen den Schrauben. Die Werte 0,01 und 0,10 gelten für weiche (nicht-

metallische) bzw. harte (metallische) Dichtungen. Eine genauere Berechnung ist in Anhang A enthalten.

## Brides et leurs assemblages - Règles de calcul des assemblages à brides circulaires avec joint - Partie 1: Méthode de calcul

1.1 Généralités

La présente partie définit une méthode de calcul des assemblages à brides boulonnées circulaires avec joint. Son objectif est d'en assurer l'intégrité structurale et la maîtrise de l'étanchéité. L'ENV 1591-2 fournit des valeurs qui peuvent être utilisées pour les caractéristiques de joints intervenant dans la méthode de calcul.

1.2 Prescription d'emploi

La présente méthode est destinée à être utilisée lorsqu'un code ou une réglementation l'exige. Elle constitue l'une des alternatives possibles (quand cela est permis), pour la justification de la conception d'un assemblage, au même titre que d'autres, par exemple :

¾ des essais spécifiques ;

¾ la référence à une expérience pratique justifiée ;

¾ l'utilisation de brides normalisées, dans les conditions autorisées.

1.3 Domaine de validité

1.3.1 Géométrie

La présente méthode est applicable aux configurations présentant :

¾ des brides dont la section correspond ou peut être assimilée à l'une de celles présentées dans les Figures 4 à 12 ;

¾ quatre boulons identiques ou plus, répartis régulièrement ;

¾ un joint dont la section et la configuration après chargement peuvent être assimilés à l'une de celles présentées en Figure 3 ;

¾ des dimensions de brides qui satisfont aux conditions suivantes :

0,2 £ bF / eF £ 5,0 ; 0,2 £ bL / eL £ 5,0 ;

eF ³ max ;

cos *S ³ 1/(1 + 0,01 ds / es)..

NOTE 1 Voir article 2 pour la signification des symboles.

NOTE 2 La condition bF / eF * 5,0 n'a pas besoin d'être satisfaite pour le collet d'une bride tournante.

NOTE 3 La condition eF x pB a pour objet de limiter l'inégalité de la répartition de la compression du joint qui peut résulter de l'espacement des boulons. Les valeurs 0,01 et 0,10 sont à utiliser respectivement pour les joints à faible dureté (non métalliques) et pour les joints durs (métalliques). Un critère plus préci

## Prirobnice in prirobnični spoji - Pravila za načrtovanje okroglih prirobničnih spojev s tesnili - 1. del: Način izračuna

### General Information

### Relations

### Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Flanges and their joints - Design rules for gasketed circular flange connections - Part 1: Calculation methodBrides et leurs assemblages - Regles de calcul des assemblages a brides circulaires avec joint - Partie 1: Méthode de calculFlansche und ihre Verbindungen - Regeln für die Auslegung von Flanschverbindungen mit runden Flanschen und Dichtung - Teil 1: BerechnungsmethodeTa slovenski standard je istoveten z:EN 1591-1:2001SIST EN 1591-1:2002en23.040.60ICS:SLOVENSKI

STANDARDSIST EN 1591-1:200201-maj-2002

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 1591-1April 2001ICS 23.040.60English versionFlanges and their joints - Design rules for gasketed circularflange connections - Part 1: Calculation methodBrides et leurs assemblages - Règles de calcul desassemblages à brides circulaires avec joint - Partie 1:Méthode de calculFlansche und ihre Verbindungen - Regeln für dieAuslegung von Flanschverbindungen mit runden Flanschenund Dichtung - Teil 1: BerechnungsmethodeThis European Standard was approved by CEN on 8 March 2001.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2001 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 1591-1:2001 E

Page 2EN 1591-1:2001ContentsPageForeword .31Scope .51.1General .51.2Requirement for use of the Calculation method .51.3Validity .52Normative references .73Notation .73.1Use of figures .73.2Subscripts and special marks .83.3Symbols .93.4Terminology .124Calculation parameters .204.1Flange parameters .204.2Bolt parameters .234.3Gasket parameters .245Internal forces (in the joint) .275.1Applied loads .275.2Compliance of the joint .285.3Minimum forces necessary for the gasket .285.4Internal forces in assembly condition (I = 0) .295.5Internal forces in subsequent conditions (I = 1, 2, .) .306Checking of the admissibility of the load ratio .316.1General .316.2Bolts .326.3Gasket .326.4Integral flange and collar .326.5Blank flange .346.6Loose flange with collar .34Annex A

(informative) Requirement for limitation of non-uniformity of gasket stress .35Annex B

(informative) Dimensions of standard metric bolts.36Annex C

(informative) Scatter of bolting-up methods .37Annex D

(informative) Assembly using torque wrench .38Annex E

(informative) Flange rotations .40 Annex F

(informative) Diagram of calculation sequence .41Annex G

(informative)

Joints with spacer seated flanges

....................................43Annex ZA (informative) Clauses of this European Standard addressing essential requirementsor other provisions of the PED .....................................................48Bibliography .....................................................................49

Page 3EN 1591-1:2001ForewordThis European Standard was prepared by the Technical Committee CEN/TC 74 "Flanges and their joints", thesecretariat of which is held by DIN.This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by October 2001, and conflicting national standards shall be withdrawn at the latestby October 2001.This European Standard has been prepared under a mandate given to CEN by the European Commission and theEuropean Free Trade Association. This European Standard is considered as a supporting standard to otherapplication and product standards which in themselves support an essential safety requirement of a New ApproachDirective and will appear as a normative reference in them.For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this standard. EN 1591 consists of two parts:– EN 1591-1 Flanges and their joints – Design rules for gasketed circular flange connections – Part 1: Calculationmethod– ENV 1591-2 Flanges and their joints – Design rules for gasketed circular flange connections – Part 2: GasketparametersThe Calculation method satisfies both leaktightness and strength criteria. The behaviour of the complete flanges-bolts-gasket system is considered. Parameters taken into account include not only basic ones such as:– fluid pressure;– material strength values of flanges, bolts and gaskets;– gasket compression factors;– nominal bolt load;but also:– possible scatter due to bolting up procedure;– changes in gasket force due to deformation of all components of the joint;– influence of connected shell or pipe;– effect of external axial forces and bending moments;– effect of temperature difference between bolts and flange ringCalculation for sealing performance is based on elastic analysis of the load/deformation relations between all partsof the flange connection, corrected by a possible plastic behaviour of the gasket material. Calculation for mechanicalresistance is based on (plastic) limit analysis of the flange-shell combination. Both internal and external loads areconsidered. Load conditions covered include initial assembly, hydrostatic test, and all significant subsequentoperating conditions. The calculation steps are broadly as follows:1) First, the required minimum initial bolt load (to be reached at bolting-up) is determined, so that in anysubsequent specified load condition, the residual force on the gasket will never be less than the minimum meanvalue required for the gasket (value is gasket data from ENV 1591-2, for instance). The determination of this loadis iterative, because it depends on the effective gasket width, which itself depends on the initial bolt load.2) Then, the internal forces that result from the selected value of initial bolt load are derived for all loadconditions, and the admissibility of combined external and internal forces is checked as follows:– bolting-up condition: the check is performed against the maximum possible bolt force that may result from thebolting-up procedure;– test and operating conditions: checks are performed against the minimum necessary forces, to ensure that theconnection will be able to develop these minimum forces without risk of yielding, except in highly localized areas.Higher actual initial bolting results in (limited) plastic deformation in subsequent conditions (test, operation).

Page 4EN 1591-1:2001But the checks so defined assure that these deformations will not reduce the bolt force to a value less than theminimum required.If necessary, the flange rotations may be estimated in all load conditions, using annex E, and the values obtained,compared with the relevant gasket limits which could apply.Checks for admissibility of loads imply safety factors which are those applied to material yield stress or strength inthe determination of the nominal design stresses used in the Calculation method.NOTE

Where flanges are used to comply with other codes the Calculation method does not specify valuesfor nominal stresses.Nevertheless, since all significant design parameters are accounted for, the use of low safety factors is madepossible by special use of nominal design stresses:– for assembly conditions the nominal design stresses have the same values as for the hydraulic pressure tests(normally higher than for operating conditions);– the nominal design stresses for the bolts are determined by the same rules as relevant for the flange and shellmaterial e.g. same safety factor on yield stress.The minimum force required on the gasket for leak tightness considerations may be established by two differentways:1) Use of tabulated gasket factors, for example those given in ENV 1591-2, which are based on industrialexperience and correspond to mainly gas and steam leak rates.2) Derivation from measured leak rate versus gasket stress data, if available for the gasket, for example as inENV 1591-2. This permits design to be based on any specified maximum leak rate.The use of this Calculation method is particularly useful for joints where the bolt load is monitored when bolting up.The greater the precision of this, the more benefit can be gained from application of the Calculation method.In the present stage of development, the Calculation method is not applicable to joints with narrow metal-to-metalcontact (with the exception of joints with spacer seated flanges (see annex G)), or to joints whose rigidity variesappreciably across gasket width.A chart illustrating the calculation process is given in annex F.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,Switzerland and the United Kingdom.

Page 5EN 1591-1:20011

Scope1.1

GeneralThis European Standard defines a Calculation method for bolted, gasketed, circular flange joints. Its purpose is toensure structural integrity and control of leaktightness. ENV 1591-2 gives values for gasket properties which can beused in the Calculation method.1.2

Requirement for use of the Calculation methodWhere permitted, the Calculation method is an alternative to design validation by other means e.g.– special testing;– proven practice;– use of standard flanges within permitted conditions.1.3

Validity1.3.1

GeometryThe Calculation method is applicable to the configurations having:– flanges whose section is given or may be assimilated to those given in Figures 4 to 12;– four or more identical bolts uniformly distributed;– gasket whose section and configuration after loading can be assimilated by one of those given in Figure 3;– flange dimension which meet the following conditions:a) 0,2 £ bF/eF £ 5,0; 0,2 £ bL/eL £ 5,0b) eF³max

e2;dB0;pB×

3(0,01.0,10)×pB/bFc) cosjs ³ 1/(1 + 0,01 ds/es)NOTE 1

For explanations of symbols see clause 3.NOTE 2

The condition bF/eF £ 5,0 need not to be met for collar in combination with loose flange.NOTE 3

The condition

is for limitation of non-uniformity of gasket pressure dueeF³pB×

3(0,01.0,10)pB/bFto spacing of bolts. The values 0,01 and 0,10 are to be applied for soft (non-metallic) and hard (metallic)gaskets respectively. A more precise criterion is given in annex A.NOTE 4

Attention may need to be given to the effects of tolerances and corrosion on dimensions; referenceshould be made to other codes under which the calculation is made, for example values are given inEN 13445 and EN 13480.The following configurations are outside the scope of the Calculation method:– flanges of essentially non-axisymmetric geometry, e.g. split loose flanges, web reinforced flanges;– flange connections having direct or indirect metal to metal contact between flanges inside and/or outside thegasket, inside and/or outside the bolt circle, except the special case of spacer-seated flanges, which is coveredin annex G.

Page 6EN 1591-1:20011.3.2

MaterialsValues of nominal design stresses are not specified in this Calculation method. They depend on other codes whichare applied, for example these values are given in EN 13445 and EN 13480.Design stresses for bolts are to be determined as for flanges and shells. The model of the gaskets is modelled byelastic behaviour with a plastic correction.For gaskets in incompressible materials which permit large deformations (for example: flat gaskets with rubber asthe major component), the results given by the Calculation method can be excessively conservative (i.e. requiredbolting load too high, allowable pressure of the fluid too low, required flange thickness too large, etc.) because itdoes not take account of such properties.1.3.3

LoadsThis Calculation method applies to the following load types:– fluid pressure: internal or external;– external loads: axial forces and bending moments;– axial expansion of flanges, bolts and gasket, in particular due to thermal effects.1.3.4

Mechanical modelThe Calculation method is based on the following mechanical model:a) Geometry of both flanges and gasket is axisymmetric. Small deviations such as those due to a finite numberof bolts, are permitted. Application to split loose flanges or oval flanges is not permitted.b) The flange ring cross-section (radial cut) remains undeformed. Only circumferential stresses and strains in thering are treated; radial and axial stresses and strains are neglected. This presupposition requires compliance withcondition 1.3.1 a).c) The flange ring is connected to a cylindrical shell. A tapered hub is treated as being an equivalent cylindricalshell of calculated wall thickness, which is different for elastic and plastic behaviour, but always between theactual minimum and maximum thickness. Conical and spherical shells are treated as being equivalent cylindricalshells with the same wall thickness; differences from cylindrical shell are explicity taken into account in thecalculation formula.This presupposition requires compliance with 1.3.1 c).At the connection of the flange ring and shell, the continuity of radial displacement and rotation is accounted forin the calculation.d) The gasket contacts the flange faces over a (calculated) annular area. The effective gasket width (radial) bGemay be less than the true width of gasket. This effective width bGe is calculated for the assembly condition (I = 0)and is assumed to be unchanged for all subsequent load conditions (I = 1,2 .). The calculation of bGe includesthe elastic rotation of both flanges as well as the elastic and plastic deformations of the gasket (approximately)in assembly condition.e) The modulus of elasticity of the gasket may increase with the compressive stress Q on the gasket. TheCalculation method uses a linear model: EG = E0 + K1 × Q. This is the unloading elasto-plastic secant modulusmeasured between 100 % and 33 % of the highest stress (Q) in assembly conditions.f) Creep of the gasket under compression is approximated by a creep factor gc (see ENV 1591-2).g) Thermal and mechanical axial deformations of flanges, bolts and gasket are taken into account.h) Loading of the flange joint is axisymmetric. Any non-axisymmetric bending moment is replaced by anequivalent axial force, which is axisymmetric according to equation (44).

Page 7EN 1591-1:2001i) load changes between load conditions cause internal changes of bolt and gasket forces. These are calculatedwith account taken of elastic deformations of all components. To ensure leaktightness, the required initialassembly force is calculated (see 5.4) to ensure that the required forces on the gasket are achieved under allconditions (see 5.3 and 5.5).j) load limit proofs are based on limit loads for each component. This approach prevents excessive deformations.The limits used for gaskets, which depend on Qmax are only approximations.The model does not take account of the following:k) Bolt bending stiffness and bending strength. This is a conservative simplification. However the tensile stiffnessof the bolts includes (approximately) the deformation within the threaded part in contact with the nut or threadedhole (see equation (34)).l) Creep of flanges and bolts. m) Different radial deformations at the gasket (this simplification has no effect for identical flanges).n) Fatigue proofs (usually not taken into account by codes like this).o) external torsional moments and external shear loads, e.g. those due to pipework.2Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).prEN 1092-1:1997Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories, PNdesignated - Part 1: Steel flangesEN 1092-2Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories, PNdesignated - Part 2: Cast iron flangesprEN 1092-3:1994Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories - Part3: Copper alloy and composite flanges, PN designatedprEN 1092-4:1995Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories, PNdesignated - Part 4: Aluminium alloy flangesENV 1591-2Flanges and their joints - Design rules for gasketed circular flange connections - Part 2:Gasket parameters3

Notation3.1

Use of figuresFigures 1 to 12 illustrate the notation corresponding to the geometric parameters. They only show principles and arenot intended to be practical designs. They do not illustrate all possible flange types for which the Calculation methodis valid.For standard flange types, according to EN 1092, the relevant figures are the following:Type 01Figure8Type 02Figure 10Type 04Figure 10Type 05Figure9Type 07Figure 10Type 11Figure4Type 12Figure 11

Page 8EN 1591-1:2001Type 13Figure 12Type 21Figure4 to 73.2

Subscripts and special marks3.2.1

SubscriptsA–Additional (FA, MA)B–BoltC–Creep of gasket (gc)D–Equivalent cylinder (tapered hub + connected shell) for load limit calculationE–Equivalent cylinder (tapered hub + connected shell) for flexibility calculationF–FlangeG–GasketH–HubI–Load condition identifier (taking values 0, 1, 2 .)L–Loose flangeM–MomentP–PressureQ–Net axial force due to pressureR–Net axial force due to external forceS–Shell, shearT–Shell, modifiedX–Weak cross-sectionD–Symbol for change or differenceav–averagec–calculatedd–designe–effectivemax–maximummin–minimumnom–nominalopt–optimalreq–requireds–non-threaded part of boltt–theoretical, torque, thread

Page 9EN 1591-1:20010–initial bolt-up condition (I = 0, see subscript I)3.2.2

Special marks~–Accent placed above symbols of flange parameters that refers to the second flange of the joint, possiblydifferent from the first3.3

SymbolsWhere units are applicable, they are shown in brackets. Where units are not applicable, no indication is given.AB–Effective total cross-section area of all bolts [mm2], equation (33)AF, AL–Gross radial cross-section area (including bolt holes) of flange ring, loose flange [mm2],equations (5), (7), (8)AGe, AGt–Gasket area, effective, theoretical [mm2], equations (39), (36)C–Coefficient to account for twisting moment in bolt load ratio, equation (71)E0–Compressive modulus of elasticity of the gasket [MPa] at zero compressive stress Q = 0 [MPa](see ENV 1591-2)EB, EF, EG, EL–Modulus of elasticity of the part designated by the subscript, at the temperature of the part[MPa] (for EG see ENV 1591-2)FA–Additional external axial force [N], tensile force > 0, compressive force < 0, see Figure 1FB–Bolt force (sum of all bolts) [N]FG–Gasket force [N]FGD–Minimum gasket force in assembly condition [N] that guarantees after all load changes tosubsequent conditions the required gasket force, equation (51)FQ–Axial fluid-pressure force [N], equation (43)FR–Force resulting from FA and MA [N], equation (44)I–Load condition identifier, for assembly condition I = 0, for subsequent conditions I = 1, 2, 3, .IB–Plastic torsion modulus [mm3] of bolt shanks , equation (71)

p12×min(dBe;dBs)3K1–Rate of change of compressive modulus of elasticity of the gasket with compressive stress,ENV 1591-2Ks–Systematic error due to the inaccuracy of the bolt tightening methodMA–Additional external moment [N × mm], Figure 1Mt–Bolt assembly torque [N × mm], annex DMt,B–twisting moment [N × mm] applied to bolt shanks as a result of application of the bolt assemblytorque Mt, equations (71) and (D.8) to (D.11)NR–Number of re-assemblies and re-tightenings during service life of joint, equation (67)P– Pressure of the fluid [MPa], internal pressure > 0, external pressure < 0 (1 bar = 0,1 MPa)NOTE

P in this standard is equal to the maximum allowable pressure PS according to the PED.

Page 10EN 1591-1:2001Q– Mean effective gasket compressive stress [MPa], Q = FG/AGeQI–Mean effective required gasket compressive stress at load condition I [MPa]Qmin–Minimum necessary compressive stress in gasket for assembly condition (on the effectivegasket area) [MPa], equation (49), (see ENV 1591-2)Qmax–Maximum allowable compressive stress in the gasket (depends on the gasket materials,construction, dimensions and the roughness of the flange facings) [MPa], equation (72), seeENV 1591-2 (including safety margins, which are same for all load conditions)Qmax,Y–Yield stress characteristic of the gasket materials and construction, see Table 1, andENV 1591-2 [MPa]TB, TF, TG, TL–Temperature (average) of the part designated by the subscript [°C] or [K], equation (45)TO–Temperature of joint at assembly [°C] or [K] (usually + 20 °C)U–Axial displacement [mm]; DU according to equation (45)WF, WL, WX–Resistance of the part and/or cross-section designated by the subscript [N × mm], equations(74), (86), (88), (90)XB, XG–Axial flexibility modulus of bolts, gasket [1/ mm], equations (34), (42)YG, YQ, YR–Axial compliance of the bolted joint, related to FG, FQ, FR [mm/N], equations (46), (47), (48) ZF, ZL–Rotational flexibility modulus of flange, loose flange [mm

3], equations (27), (31), (32)b0–Width of chamfer (or radius) of a loose flange [mm] see Figure 10, equation (15) such that:d7min = d6+2×b0bF, bL–Effective width of flange, loose flange [mm], equations (5) to (8)bGi, bGe, bGt–Gasket width (radial), interim, effective, theoretical [mm], equations (35), (38), Table 1cF, cM, cS–Correction factors, equations (20), (78), (79)d0–Inside diameter of flange ring [mm] and also the outside diameter of central part of blank flange(with thickness e0), in no case greater than inside diameter of gasket [mm], Figures 4 to 12d1–Average diameter of hub, thin end [mm], Figures 4, 5, 11 and 12d2–Average diameter of hub, thick end [mm], Figures 4, 5, 11 and 12d3, d3e–Bolt circle diameter, real, effective [mm], Figures 4 to 12d4–Outside diameter of flange [mm], Figures 4 to 12d5, d5t, d5e–Diameter of bolt hole, pierced, blind, effective [mm], Figures 4 to 12d6–Inside diameter of loose flange [mm], Figures 10, 12d7–Diameter of position of reaction between loose flange and stub or collar [mm], Figure 1,equations (15), (41)d8–Outside diameter of collar [mm], Figure 10d9–Diameter of a central hole in a blank flange [mm], Figure 9dB0, dBe, dBs–Diameter of bolt: nominal diameter, effective diameter, shank diameter [mm], Figure 2,Table B.1dB2, dB3–Basic pitch diameter, basic minor diameter of thread [mm], see Figure 2

Page 11EN 1591-1:2001dGe, dGt–Diameter of gasket, effective, theoretical [mm], Figure 3, Table 1dG1, dG2–Inside, outside diameter of theoretical contact area of gasket [mm], Figure 3dE, dF, dL–Average diameter of part or section designated by the subscript [mm], equations (5) to (8), (10)dS, dXto (12), Figures 4 to 12e0–Wall thickness of central plate of blank flange within diameter d0 [mm], Figure 9e1–Minimum wall thickness at thin end of hub [mm], Figures 4, 5, 11, 12e2–Wall thickness at thick end of hub [mm], Figures 4, 5, 11, 12eD, eE–Wall thickness of equivalent cylinder for load limit calculations, for flexibility calculations [mm],equations (9), (11), (12), (75)eF, eL–Effective axial thickness of flange, loose flange [mm], equations (5) to (8)eFb–Thickness of flange ring at diameter d3 (bolt position) [mm] equation (3)eFt–Thickness of flange ring at diameter dGe (gasket force position), relevant for thermal expansion[mm], equation (45)eG–Thickness fo gasket [mm], Figure 3eP, eQ–Part of flange thickness with (eP), without (eQ) radial pressure loading [mm], Figures 4 to 12,such that eP+eQ = eFeS–Thickness of connected shell [mm], Figures 4 to 8, 10 to 12eX–Flange thickness at weak section [mm], Figure 9fB, fE, fF, fL, fS–Nominal design stress [MPa] of the part designated by the subscript, at design temperature [°C]or [K], as defined and used in pressure vessel codesgC–Creep factor for gasket, equation (46), see ENV 1591-2hG, hH, hL–Lever arms [mm], Figure 1, equations (14), (16)hP, hQ, hR,–Lever arm corrections [mm], equations (13), (21) to (24), (29), (30)hS, hTjM, jS–Sign number for moment, shear force (+1 or

1), equation (80)kQ, kR, kM, kS–Correction factors, equation (25), (26), (81)lB, ls–Bolt axial dimensions [mm], Figure 2, equation (34)le–le = lB

lslH–Length of hub [mm], Figures 4, 5, 11, 12, equation (9), (75)nB–Number of bolts, equations (1), (4), (33), (34)pB–Pitch between bolts [mm], equation (1)pt–Pitch of bolt thread [mm], Table B.1r0, r1–Radii [mm], Figures 4, 10r2–Radius of curvature in gasket cross-section [mm], Figure 3DU–Differential axial expansions [mm], equation (45)

Page 12EN 1591-1:2001QF, QL–Rotation of flange, loose flange, due to applied moment [rad], annex EY–Load ratio of flange ring due to radial force, equation (82)YZ–Particular value of Y, equation (74), Table 2FB, FF, FG,–Load ratio of part and/or cross-section designated by the subscript, to be calculated for all loadFL, FXconditions, equation (71), (72), (73), (85), (87), (89), (91)Fmax–Reduced maximum allowable load ratio, equation (70)aB, aF, aG, aL–Thermal expansion coefficient of the part designated by the subscript, averaged between T0 andTB, TF, TG, TL, TS, [K-1]b, g, d, J–Intermediate variables, equations (9), (17), (18), (19), (41), (70), (75), (77)k, l, c

1+,

1 –Scatter of initial bolt load of a single bolt, above nominal value, below nominal value, annex C +,

–Scatter for the global load of all the bolts above nominal value, below nominal value, equations(60), (61)p–Numerical constant (p = 3,141593)jG–Angle of inclination of a sealing face [rad or deg], Figure 3, Table 2jS–Angle of inclination of connected shell wall [rad or deg], Figures 6, 73.4

Terminology3.4.1

FlangesIntegral flange:Flange attached to the shell either by welding (e.g. neck weld, see Figures 4 to 7 or slip onweld see Figures 8 and 11) or cast onto the envelope (integrally cast flanges, type 21)Blank flange:Flat closure, Figure 9Loose flange:Separate flange ring abutting a collar, Figure 10Hub:Axial extension of flange ring, usually connecting flange ring to shell, Figures 4, 5Collar:Abuttment for a loose flange, Figure 103.4.2

LoadingExternal loads:Forces and/or moments applied to the joint by attached equipment, e.g. weight and thermalexpansion of pipes.3.4.3

Load conditionsLoad condition:State with set of applied simultaneous loads; designated by I.Assembly condition:Load condition due to initial tightening of bolts (bolting up), designated by I = 0Subsequent condition:Load condition subsequent to assembly condition, e.g. test condition, operating condition,conditions arising during start-up and shut-down; designated by I = 1, 2, 3 .3.4.4

CompliancesCompliance:Inverse stiffness (axial), symbol Y, [mm/N]

Page 13EN 1591-1:2001Flexibility modulus:Inverse stiffness modulus, excluding elastic constants of material:axial: symbol X, [1/mm] rotational:symbol Z, [1/mm3]Figure 1 — Loads and lever armsle = lB

lsFigure 2 — Bolts

Page 14EN 1591-1:2001

3a 3b 3c 3

**...**

## Questions, Comments and Discussion

## Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.