SIST EN ISO 10441:2009

SLOVENSKI STANDARD
01-februar-2009
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Petroleum, petrochemical and natural gas industries - Flexible couplings for mechanical
power transmission - Special-purpose applications (ISO 10441:2007)
Erdöl- und Erdgasindustrie - Nachgiebige Kupplungen zur mechanische
Kraftübertragung - Besondere Anwendungsfälle (ISO 10441:2007)
Industries du pétrole, de la pétrochimie et du gaz naturel - Accouplements flexibles pour
transmission de puissance mécanique - Applications spéciales (ISO 10441:2007)
Ta slovenski standard je istoveten z: EN ISO 10441:2007
ICS:
21.120.20 Sklopke Couplings
75.180.20 Predelovalna oprema Processing equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 10441
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2007
ICS 75.180.20 Supersedes EN ISO 10441:1999
English Version
Petroleum, petrochemical and natural gas industries - Flexible
couplings for mechanical power transmission - Special-purpose
applications (ISO 10441:2007)
Industries du pétrole, de la pétrochimie et du gaz naturel - Erdöl- und Erdgasindustrie - Nachgiebige Kupplungen zur
Accouplements flexibles pour transmission de puissance mechanische Kraftübertragung - Besondere
mécanique - Applications spéciales (ISO 10441:2007) Anwendungsfälle (ISO 10441:2007)
This European Standard was approved by CEN on 28 February 2007.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN 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 translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10441:2007: E
worldwide for CEN national Members.

Foreword
This document (EN ISO 10441:2007) has been prepared by Technical Committee ISO/TC 67
"Materials, equipment and offshore structures for petroleum and natural gas industries" in
collaboration with Technical Committee CEN/TC 12 "Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries", the secretariat of which is
held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by September 2007, and conflicting national
standards shall be withdrawn at the latest by September 2007.

This document supersedes EN ISO 10441:1999.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United
Kingdom.
Endorsement notice
The text of ISO 10441:2007 has been approved by CEN as EN ISO 10441:2007 without any
modifications.
INTERNATIONAL ISO
STANDARD 10441
Second edition
2007-03-15
Petroleum, petrochemical and natural gas
industries — Flexible couplings for
mechanical power transmission —
Special-purpose applications
Industries du pétrole, de la pétrochimie et du gaz naturel —
Accouplements flexibles pour transmission de puissance mécanique —
Applications spéciales
Reference number
ISO 10441:2007(E)
©
ISO 2007
ISO 10441:2007(E)
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©  ISO 2007
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Published in Switzerland
ii © ISO 2007 – All rights reserved

ISO 10441:2007(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Statutory requirements .7
5 Coupling selection.7
6 Coupling design.9
7 Coupling ratings .11
8 Coupling requirements .12
8.1 Metallic flexible-element couplings .12
8.2 Machining .12
8.3 Spacer .13
8.4 Hub type.13
8.5 Integral flanges .13
8.6 Hubs .13
8.7 Solo plate (idling adapter).15
8.8 Moment simulator.15
8.9 Component fit tolerances and potential unbalance calculations .15
8.10 Fasteners (including studs).15
8.11 Electrical insulation.16
8.12 Dynamics .16
9 Balance .17
9.1 General.17
9.2 Balancing methods.18
9.3 Balance criteria .20
9.4 Trim balance holes .23
10 Materials .24
11 Accessories.24
12 Manufacturing quality, inspection, testing and preparation for shipment .25
12.1 Manufacturing quality .25
12.2 Inspection and testing.25
12.3 Inspection .26
12.4 Testing .26
12.5 Preparation for shipment .27
13 Vendor data .27
13.1 General.27
13.2 Proposals and contract data .28
Annex A (normative) Torsional damping couplings and resilient couplings .31
Annex B (normative) Gear couplings.34
Annex C (normative) Quill-shaft couplings .36
Annex D (informative) Factors for metallic element couplings .37
Annex E (informative) Example of the determination of potential unbalance .39
ISO 10441:2007(E)
Annex F (informative) Examples of misalignments . 43
Annex G (informative) Coupling tapers. 44
Annex H (normative) Coupling guards. 45
Annex I (informative) Procedure for residual unbalance check . 47
Annex J (informative) Coupling datasheets. 51
Bibliography . 56

iv © ISO 2007 – All rights reserved

ISO 10441:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 10441 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 6, Processing equipment and
systems.
This second edition cancels and replaces the first edition (ISO 10441:1999), which has been technically
revised.
ISO 10441:2007(E)
Introduction
This International Standard was developed from the API Std 671, 3rd edition, 1998. It is intended that the 4th
edition of API Std 671 will be identical to this International Standard.
Users of this International Standard should be aware that further or differing requirements may be needed for
individual applications. This International Standard is not intended to inhibit a vendor from offering, or the
purchaser from accepting alternative equipment or engineering solutions for the individual application. This
may be particularly appropriate where there is innovative or developing technology. Where an alternative is
offered, the vendor should identify any variations from this International Standard and provide details.
This International Standard requires the purchaser to specify certain details and features.
A bullet (●) at the beginning of a subclause or paragraph indicates that either a decision is required or further
information is to be provided by the purchaser. This information should be indicated on the datasheet(s),
typical examples of which are included as Annex J; otherwise it should be stated in the quotation request or in
the order.
vi © ISO 2007 – All rights reserved

INTERNATIONAL STANDARD ISO 10441:2007(E)

Petroleum, petrochemical and natural gas industries —
Flexible couplings for mechanical power transmission —
Special-purpose applications
1 Scope
This International Standard specifies the requirements for couplings for the transmission of power between the
rotating shafts of two machines in special-purpose applications in the petroleum, petrochemical and natural
gas industries. Such applications are typically in large and/or high speed machines, in services that can be
required to operate continuously for extended periods, are often unspared and are critical to the continued
operation of the installation. By agreement, it can be used for other applications or services.
Couplings covered by this International Standard are designed to accommodate parallel (or lateral) offset,
angular misalignment and axial displacement of the shafts without imposing unacceptable mechanical loading
on the coupled machines. It is applicable to gear, metallic flexible element, quill shaft and torsionally resilient
type couplings. Torsional damping and resilient type couplings are detailed in Annex A; gear-type couplings
are detailed in Annex B and quill shaft style couplings are detailed in Annex C.
This International Standard covers the design, materials of construction, manufacturing quality, inspection and
testing of special-purpose couplings.
This International Standard does not define criteria for the selection of coupling types for specific applications.
This International Standard is not applicable to other types of couplings, such as clutch, hydraulic, eddy-
current, rigid, radial spline, chain and bellows types.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 262, ISO general-purpose metric screw threads — Selected sizes for screws, bolts and nuts
ISO 286-2, ISO system of limits and fits — Part 2: Tables of standard tolerance grades and limit deviations for
holes and shafts
ISO 2491, Thin parallel keys and their corresponding keyways (Dimensions in millimetres)
1)
ANSI Y14.2M , Line Conventions and Lettering
2)
ANSI/AGMA 9000 , Flexible Couplings — Potential Unbalance Classification
ANSI/AGMA 9002, Bores and Keyways for Flexible Couplings (Inch Series)
ANSI/AGMA 9003, Flexible Couplings — Keyless Fits

1) American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA.
2) American Gear Manufacturers Association, 500 Montgomery Street, Suite 350, Alexandria, VA 22314-1560, USA.
ISO 10441:2007(E)
ANSI/AGMA 9004, Flexible Couplings — Mass Elastic Properties and other Characteristics (Inch Series)
ANSI/AGMA 9104, Flexible Couplings — Mass Elastic Properties and other Characteristics (Metric Series)
ANSI/AGMA 9112, Bores and Keyways for Flexible Couplings (Metric Series)
3)
ANSI/ASME B1.1 , Unified inch screw threads, UN and UNR thread form
4)
DIN 7190 , Interference fits — Calculation and design rules
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
angular misalignment
〈double-engagement couplings〉 two minor angles between the extension of each machine centreline and the
centreline of the structure joining the two flexible elements
3.2
angular misalignment
〈single-engagement couplings〉 minor angle between the extensions of two machine-shaft centrelines
NOTE If the shaft centrelines do not intersect, a single-engagement coupling is not appropriate.
3.3
assembly balance
procedure in which a completely assembled coupling is balanced as a unit
3.4
assembly balance check
procedure in which an assembled coupling is placed on a balancing machine and the residual unbalance is
measured
NOTE An assembly balance check can be carried out on a component balanced coupling, or on an assembly-
balanced coupling.
3.5
axial displacement
change in the relative axial position of the adjacent shaft ends of two coupled machines, usually caused by
thermal expansion
3.6
component balance
procedure for achieving coupling balance in which the components or factory assembled sub-assemblies are
balanced separately before assembly of the coupling
3.7
continuous torque rating
coupling manufacturer’s declared maximum torque that the coupling is capable of transmitting continuously for
unlimited periods
3) ASME International, Three Park Avenue, New York, NY 10016-5990, USA.
4) Deutsches Institut fur Normung, Burggrafenstrasse 6, Sresemannallee 15, Berlin, Germany D-10787.
2 © ISO 2007 – All rights reserved

ISO 10441:2007(E)
3.8
crown diameter
major diameter of the external teeth of a gear-type coupling
3.9
distance between shaft ends
DBSE
distance from the extreme end of one shaft (including any threaded end) to the extreme end of the next shaft
or, in the case of integral flanges, the distance from the mating faces
3.10
double engagement coupling
coupling with two planes of flexure
NOTE This arrangement enables couplings of certain types, notably gear and metallic flexible element types, that
cannot normally accommodate parallel (or lateral) offset, to do so.
3.11
factor of safety
factor that is used to cover uncertainties in a coupling design
EXAMPLES Analytical assumptions in stress analysis, material properties, manufacturing tolerances, etc.
NOTE Under given design conditions, the factor of safety is the material yield strength divided by the calculated
stress, where the stress is a function of torque, speed, misalignment and axial displacement.
3.12
fatigue factor of safety
factor of safety at the published continuous rated conditions of torque, speed, misalignment and axial
displacement, used by the manufacturer to establish the coupling rating
See 7.1.
NOTE The fatigue factor of safety is further explained and defined in Annex D.
3.13
flex-hub coupling
gear-type coupling with the external teeth on the hubs and the internal teeth in the sleeves
3.14
gear coupling
coupling of the mechanical contact type that transmits torque and accommodates angular misalignment,
parallel offset and axial displacement by relative rocking and sliding motion between mating, profiled gear
teeth
3.15
half coupling
composite of all of the components of the coupling attached to, and supported from, one shaft including an
appropriate portion of the spacer assembly in the case of a double-engagement coupling or of the flexing
elements of a single-engagement coupling
3.16
idling adapter
solo plate
device designed to rigidly hold in alignment the floating parts of certain types of couplings to allow uncoupled
operation of the driving or driven machine without dismounting the coupling hub
ISO 10441:2007(E)
3.17
lateral offset
lateral distance between the centrelines of two shafts, which are not parallel, measured perpendicularly to the
centreline and in the plane of the shaft end of the driving machine
See Annex F.
3.18
manufacturer
agency responsible for the design and fabrication of the coupling
NOTE The manufacturer is not necessarily the vendor.
3.19
maximum allowable temperature
maximum continuous temperature for which the manufacturer has designed the coupling
3.20
maximum continuous angular misalignment
maximum angular misalignment at each plane of flexure that the coupling is able to tolerate for unlimited
periods
NOTE Maximum continuous angular misalignment can be expressed as either
a) a single value when transmitting the coupling continuous torque rating at the coupling rated speed, and
simultaneously subjected to the coupling maximum continuous axial displacement, or
b) a range of values expressed as an inter-related function of speed, torque, and axial displacement.
3.21
maximum continuous axial displacement
maximum axial displacement the coupling is able to tolerate for unlimited periods
NOTE Maximum continuous axial displacement can be expressed as either
a) a single value when transmitting the coupling continuous torque rating at the coupling rated speed and
simultaneously subjected to the coupling maximum continuous angular misalignment, or
b) a range of values expressed as an inter-related function of speed, torque, and angular misalignment.
3.22
maximum continuous speed
highest rotational speed at which the coupling, as made and tested, is capable of continuous operation
3.23
metallic flexible-element coupling
coupling type that obtains its flexibility from the flexing of thin metallic discs, diaphragms or links
3.24
moment simulator
auxiliary device intended to simulate the moment of the mass of a half coupling
NOTE A moment simulator can also be designed to serve as an idling adapter (solo plate).
3.25
momentary torque limit
torque that corresponds to a factor of safety of 1,0 with respect to the most highly stressed component’s
material yield strength, allowing for a combination of speed, angular misalignment and axial displacement
4 © ISO 2007 – All rights reserved

ISO 10441:2007(E)
3.26
normal operating point
point at which usual operation is expected
NOTE This point is usually the point at which the machine manufacturer(s) certify(ies) that performance is within the
tolerances stated to the owner.
3.27
owner
final recipient of the equipment, who may delegate another agent as the purchaser of the equipment
3.28
parallel offset
distance between the centrelines of two coupled shafts that are parallel but not in the same straight line
See Annex F.
3.29
peak torque rating
maximum torque the coupling can tolerate for short periods
3.30
pilot
rabbet
register
surface that positions a coupling component, sub-assembly, or assembly radially with respect to another
coupling component
3.31
potential unbalance
probable net unbalance of a complete coupling
NOTE 1 Potential unbalance results from a combination of the residual unbalance of individual components and sub-
assemblies and possible eccentricity of the components and sub-assemblies due to run-out and tolerances of the various
surfaces and registers. Since it can be assumed that the actual values of the various contributory unbalances are random
in both magnitude and direction, the numerical value of the potential unbalance is the square root of the sum of the
squares of all the contributory unbalances. Typical contributory unbalances are
a) the residual unbalance of each component or sub-assembly,
b) errors in the balance of each component or sub-assembly resulting from eccentricity in the fixture used to mount the
component or sub-assembly in the balance machine,
c) the unbalance of each component or sub-assembly due to eccentricity resulting from clearance or run-out of the
relevant registers or fits.
NOTE 2 The concept of potential unbalance is explained more fully and a worked example is provided in Annex E.
3.32
purchaser
agency that issues the order and the specification to the vendor
NOTE The purchaser can be the owner of the plant in which the equipment is to be installed, the owner’s appointed
agent or, frequently, the manufacturer of the driven machine.
3.33
quill-shaft coupling
coupling that is both laterally and torsionally flexible, with angular misalignment, parallel offset and torsional
fluctuations being accommodated by elastic deformation of a relatively long, slender shaft
NOTE Quill-shaft couplings, unless combined with another type, cannot accommodate axial displacement.
ISO 10441:2007(E)
3.34
rated speed
highest rotational speed at which the coupling is required to be capable of transmitting the continuous torque
rating while simultaneously subjected to the rated angular misalignment and the coupling rated axial
displacement
3.35
residual unbalance
level of unbalance remaining in a component or assembly after it has been balanced, either to the limit of the
capability of the balancing machine or in accordance with the relevant standard
3.36
service factor
factor applied to the steady-state torque in order to allow for off-design conditions, cyclic and other variations
as well as equipment variations resulting in higher torque than that at the equipment normal operating point
NOTE Service factor is not the same as the factor of safety, 3.11 or the fatigue factor of safety, 3.12.
3.37
single-engagement coupling
coupling with only one plane of flexure
NOTE This type of coupling can accommodate angular misalignment and axial displacement. Single-engagement
couplings of some types, notably gear and metallic flexible element types, do not normally accommodate parallel (or
lateral) offset. Certain types of single-engagement couplings (not covered by this International Standard) can
accommodate offset misalignment to a limited extent.
3.38
spacer
part of a coupling that is removable to give access for maintenance and/or removal of the coupling hubs
NOTE The spacer can be a single component or an assembly.
3.39
spacer gap length
distance between coupling hubs or sleeves in which the coupling spacer is installed
NOTE Spacer gap length is not necessarily equal to the distance between the shaft ends.
3.40
torsional damping
absorption or dissipation of oscillatory rotary energy
NOTE Torsional damping is necessary in some cases to limit the build-up of steady-state torsional resonant
oscillations in a system.
3.41
torsional natural frequency
frequency of the undamped, free-rotational vibration of a system composed of revolving mass inertias acting
in combination with the restraining torsional rigidities of the connected shafts and couplings
3.42
torsionally resilient coupling
coupling with increased flexibility in a rotational direction, increased capability to recover from flexing and with
hysteresis capability
NOTE Resilience is the ability to recover from deformation under repeated flexing, taking account of energy storage
and hysteresis effects. Some types of torsionally resilient couplings can also be designed to accommodate misalignment
and/or axial displacement.
6 © ISO 2007 – All rights reserved

ISO 10441:2007(E)
3.43
torsional stiffness
ratio of the applied torque to the resulting torsional displacement of either a complete coupling or part of the
coupling, such as a spacer
NOTE With some types of couplings, the torsional stiffness is not constant but is a function of the magnitude of the
torque and, with oscillating torques, also the frequency.
3.44
total indicator reading
TIR
difference between the maximum and minimum readings of a dial indicator or similar device, monitoring a face
or cylindrical surface during one complete revolution of the monitored surface
NOTE 1 For a perfectly cylindrical surface, the total indicator reading implies an eccentricity equal to half the reading.
For a perfectly flat face, the total indicator reading implies an out-of-squareness equal to the reading. If the surface in
question is not perfectly cylindrical or flat, the interpretation of the meaning of total indicator reading is more complex and
can represent ovality or lobing.
NOTE 2 Total indicator reading is also known as “full indicator movement”.
3.45
unit responsibility
responsibility for co-ordinating the delivery and technical aspects of the equipment and all auxiliary systems
included in the scope of the order
NOTE The technical aspects to be considered include, but are not limited to, such factors as the power requirements,
speed, rotation, general arrangement, dynamics, noise, lubrication, sealing system, material test reports, instrumentation,
piping, conformance to specifications and testing of components.
3.46
vendor
supplier
agency that supplies the equipment
NOTE The vendor is the manufacturer of the equipment or the manufacturer’s agent and normally is responsible for
service support.
4 Statutory requirements
The purchaser and the vendor shall mutually determine the measures to be taken to comply with any federal,
state or local codes, regulations, ordinances or rules that are applicable to the equipment.
5 Coupling selection
z 5.1 The purchaser shall specify the type of coupling required. Unless otherwise specified, the coupling shall
be a metallic flexible-element coupling. For torsional damping and resilient couplings, refer to Annex A; for
gear couplings, refer to Annex B; and for quill-shaft couplings, refer to Annex C.
5.2 The coupling shall be selected based on the equipment loading and shall be capable of transmitting the
maximum steady-state torques, cyclic torques, and the maximum transient torques under all conditions of
angular misalignment, axial displacement, speed and temperature, simultaneously, to which it will be
subjected in service.
In general, a special-purpose coupling shall be designed and constructed for a minimum service life of five
years for flexible element couplings and three years for gear and torsional damping and resilient couplings.
Figure 1 provides guidance for the typical selection process for a coupling.
z 5.3 If specified, the coupling, coupling-to-shaft juncture and shafting may be sized for a future condition.
ISO 10441:2007(E)
Figure 1 — Typical coupling selection process
8 © ISO 2007 – All rights reserved

ISO 10441:2007(E)
6 Coupling design
z 6.1 The purchaser shall specify the following requirements, where applicable:
a) type of train;
b) normal power;
c) normal speed and variations;
d) maximum continuous speed;
e) any defined overspeed;
f) angular misalignment;
g) axial displacements;
h) shaft sizes and styles;
i) distance between shaft-ends;
j) temperature;
k) type of driver;
l) driver power rating (list and driver service factor);
m) expected transient (peak) and cyclic torque conditions, including magnitude, nature and number of
occurrences of transients to which the coupling will be subjected in service.
z 6.2 The purchaser shall specify the maximum angular misalignments the coupling is expected to
experience during start-up, normal operation and shut-down of the coupled machines, normally expressed as
parallel (or lateral) offset and/or angular misalignment between the coupled shafts. These values shall allow
for all the known effects on the machines from thermal, pressure and dynamic forces. Unless otherwise
specified, the steady-state angular misalignment capability across each flexible element shall be not less than
0,2°.
z 6.3 The purchaser shall specify the maximum axial displacements the coupling is expected to experience,
expressed as the amount and direction of the relative movement of the shaft ends toward or away from each
other as the coupled machines go through their start-up, normal operation and shut-down cycle. These
dimensions shall be given from the machine at ambient conditions, non-operating position. Unless otherwise
specified, the minimum steady-state axial deflection (plus/minus) capability shall be determined by the largest
shaft diameter divided by 125.
z 6.4 The purchaser shall specify the speed range for the fully assembled coupling, moment simulator and
solo plate for both continuous speed and any defined overspeed.
6.5 The steady-state torque, T , expressed in newton-metres (inch-pounds force), shall be determined as
n
given in Equation (1):
KP×
1normal
T = (1)
n
N
normal
where
K is a constant, equal to 9 550 (63 000);
ISO 10441:2007(E)
P is the input power required by the driven machine at the specified normal operating point,
normal
expressed in kilowatts (horsepower);
N is the speed corresponding to the normal power, expressed in revolutions per minute.
normal
z If specified by the purchaser, the steady-state torque shall be based on the power required by the driven
machine at the rated operating point and the corresponding speed rather than that at the normal operating
point. This can be appropriate if the power required by the driven machine at the rated point is significantly
higher than that at the normal point.
NOTE 1 This situation can occur, for example, in the case of a centrifugal compressor with a number of different
specified operating duties.
NOTE 2 Basing the coupling torque rating on the driven-machine-rated operating point rather than the normal point can
result in a coupling that is undesirably large or heavy. This can be significant if one or both of the connected machines is
sensitive to overhung mass.
The purchaser should also consider possible future up-rating of the connected machines, for example
augmentation of the power output of a gas turbine by water injection.
6.6 Unless otherwise specified, the steady-state selection torque, T , expressed in newton-metres (inch-
s
pounds), used to select the coupling shall be as given in Equation (2):
TT=×F (2)
sn S
where F is the service factor (as specified for the specific coupling type).
S
NOTE The service factor allows for various modes of off-design operation that can result from such factors as a
change in density of the fluid (molar mass, temperature or pressure variation), unequal load sharing, fouling or driver
output at maximum conditions.
6.7 Unless otherwise specified, the coupling shall have, as a minimum, a service factor of 1,5 for a metallic
flexible-element coupling.
6.8 The service factor may be reduced by agreement between the purchaser and the vendor if
a) the characteristics of the driver and driven machines and the operating process are well understood, or
b) all reasonable attempts to achieve the specified steady-state torque service factor fail to result in a
coupling mass and subsequent overhung moment commensurate with the requirement for rotor dynamics
of the connected machines.
In no case shall the service factor be reduced to a value lower than 1,2 based on the normal power.
z 6.9 If specified, for the steady-state conditions, the coupling shall be sized based on the driver rating
multiplied by 1,2 (typically, excluding the driver service factor).
NOTE If the driver rating is large compared with the normal load, this requirement can result in an excessively
conservative coupling selection.
6.10 If the machine train is driven by an induction motor, the coupling, coupling-to-shaft juncture and the
machinery shafting shall be capable of transmitting 115 % of the expected transient (peak) torque
encountered during a start-up without damage.
6.11 If the machine train is driven by a synchronous motor, the coupling shall be capable of withstanding the
cyclic torque associated with start-up for the expected number of starts specified by the purchaser. A limited
life fatigue stress analysis shall be carried out to verify this.
NOTE For initial coupling selection, a large cyclic torque requirement is typically assumed until all conditions are
known so that the torsional response analysis can be completed.
10 © ISO 2007 – All rights reserved

ISO 10441:2007(E)
z 6.12 If specified, the coupling shall be capable of transmitting a specified transient torque associated with a
generator short circuit and/or a motor breaker re-closure without damage.
NOTE During these situations large torques can occur, which require that the total system be subsequently examined
for possible damage.
6.13 Unless otherwise specified, the coupling-to-shaft juncture and the machinery shafting shall be capable
of operating at a steady-state torque determined in accordance with 6.6, substituting a service factor of 1,75.
6.14 Unless otherwise agreed, the torque capacity of a coupling-to-shaft juncture that is hydraulically fitted
and keyless shall be determined by using the methods and equations in ANSI/AGMA 9003 or DIN 7190. Other
methods of calculation may be used with the approval of the purchaser.
The coefficient of friction used shall be 0,15.
The assumed length of hub engagement shall not include “O”-ring and oil-distribution grooves in the hub or
the shaft.
6.15 Couplings may be designed to transmit torque through flange face friction. Unless otherwise agreed, a
value of 0,15 shall be assumed for the coefficient of friction. However, the fasteners for coupling flanges,
including integral flanges, shall be not less than that required to transmit the specified torques, as identified in
6.9 through 6.12, in shear.
7 Coupling ratings
7.1 The vendor shall state the continuous torque rating at the rated speed, when simultaneously subjected
to the maximum continuous angular misalignment and the maximum continuous axial displacement. The
fatigue factor of safety at the continuous torque rating and any published combination of speed, angular
misalignment and axial displacement shall be determined using the proportional increase method with either
the modified Goodman diagram or constant-life curves (see Annex D), together with the mean and cyclic
stresses induced in the flexible element under the evaluated conditions. If the modified Goodman diagram is
used, the fatigue factor of safety shall be not less than 1,25. If the constant-life curve is used, the fatigue factor
of safety shall be not less than 1,35. Regardless of the method used, data for material strength shall be drawn
from published industry standards or test data.
NOTE This subclause defines (for the coupling manufacturer) the minimum fatigue factors of safety and the methods
for applying them to recognized material properties. This definition standardizes the basis for continuous coupling ratings.
Details of the design, such as equations and analysis used to derive the stresses, are often considered proprietary and are
not a point of documentation.
7.2 The vendor shall state the peak torque rating of the coupling. With the coupling subjected
simultaneously to its peak torque rating and rated conditions of speed, axial displacement and angular
misalignment, all torque-transmitting coupling components shall have a factor of safety not less than 1,15 with
respect to the component’s material yield strength. The manufacturer shall also state the momentary torque
limit that corresponds to a factor of safety of 1,0 with respect to the yield strength of the most highly stressed
component.
The vendor shall advise which components, if any, should be inspected and/or replaced following th
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