SIST EN IEC 63230:2026

Fatigue assessment of hydraulic turbine runners: from design to quality assurance (IEC 63230:2026)

This International Standard applies to runners of reaction turbines, regardless of their size and capacity. These can include radial turbines such as Francis turbines, axial turbines such as Kaplan and propeller turbines, as well as diagonal turbines, in all possible configurations. In the case of turbine runners with adjustable blades, the internal mechanical components of the blades' adjustment mechanism are excluded from this document. Pelton turbines, storage pumps and pump-turbines are not covered in this first edition, even though several topics are applicable to these types of hydraulic machines. Specificities and applicability to Pelton turbine and pump-turbines will be discussed in a later revision of the standard
This document outlines the methodologies for conducting a fatigue assessment of turbine runners. It encompasses several key aspects, such as defining the load events to be considered during the assessment, determining stresses for each of these load events, as well as the detailed approaches for assessing fatigue of new and existing runners. Additionally, it includes manufacturing and quality assurance requirements to be complied with to achieve the desired material fatigue properties and effectively apply the proposed fatigue assessment methodologies. This document also contains best practices for performing and analysing onsite strain gauge measurements performed on existing runners to evaluate their fatigue life.
The purpose of this document is to provide guidelines to assess fatigue in new and existing turbine runners. It does not specify if a fatigue assessment should be performed or not for a given runner. However, Annex B provides guidance to evaluate the necessity of realizing a fatigue assessment or not for a given new runner. The methods described in this document can also be used for remaining life assessments of in-service runners. However, it is important to consider that the assessed runner materials' fatigue properties and quality level could differ from the prescriptions found in the manufacturing and quality assurance section of this document which have been defined for new runners. It is also important to mention that fatigue assessment alone is not sufficient for a complete validation of the mechanical integrity of a new runner design. Other mechanical validations not covered in this document are typically conducted.

Lebensdauerbewertung von Laufrädern hydraulischer Turbinen: vom Design bis zur Qualitätssicherung (IEC 63230:2026)

Évaluation de la fatigue des roues de turbines hydrauliques: de la conception à l'assurance qualité (IEC 63230:2026)

IEC 63230:2026 s'applique aux roues de turbines à réaction, quelles que soient leur taille et leur capacité. Elle peut couvrir les turbines radiales comme les turbines Francis, les turbines axiales comme les turbines Kaplan et les turbines hélices, ainsi que les turbines diagonales, dans toutes les configurations géométriques possibles. Dans le cas des turbines à pales orientables, les composants mécaniques internes du mécanisme de commande des pales sont exclus du présent document. Les turbines Pelton, les pompes d'accumulation et les pompes‑turbines ne sont pas couvertes dans cette première édition, même si plusieurs aspects s'appliquent à ces types de machines hydrauliques. Les spécificités et les aspects relatifs aux turbines Pelton et aux pompes‑turbines seront traités dans une révision ultérieure de la norme.
Le présent document décrit les méthodologies pour effectuer une évaluation de la fatigue des roues de turbines. Il couvre plusieurs aspects clés, notamment la définition des événements‑charge à prendre en compte, la détermination des contraintes pour chacun de ces événements‑charge, ainsi que les approches détaillées pour effectuer cette évaluation à la fatigue de roues neuves et existantes. En outre, il définit les exigences de fabrication et d'assurance qualité à respecter pour obtenir les propriétés de fatigue souhaitées sur les matériaux considérés de sorte à se conformer efficacement aux méthodologies d'évaluation en fatigue proposées. Le présent document fournit également les meilleures pratiques pour effectuer et analyser des mesures de jauges extensométriques sur des roues existantes afin d'évaluer leur durée de vie en fatigue.
Le présent document a pour objet de fournir des lignes directrices pour effectuer une évaluation de la fatigue des roues neuves et existantes. Il ne spécifie pas s'il convient d'effectuer une évaluation en fatigue ou non pour une roue donnée. Cependant, l'Annexe B propose des recommandations pour évaluer la nécessité ou non de procéder à une évaluation en fatigue d'une roue neuve donnée. Les méthodes décrites dans le présent document peuvent également être utilisées pour les évaluations de durée de vie résiduelles de roues en service

Ocena utrujenosti rotorjev hidravličnih turbin: od zasnove do zagotavljanja kakovosti (IEC 63230:2026)

Ta mednarodni standard se uporablja za rotorje reakcijskih turbin, ne glede na njihovo velikost in zmogljivost. To lahko vključuje radialne turbine, kot so Francisove turbine, aksialne turbine, kot so Kaplanove in propelerne turbine, ter diagonalne turbine v vseh možnih konfiguracijah. V primeru rotorjev turbin z nastavljivimi lopaticami so notranje mehanske komponente mehanizma za nastavitev lopatic izključene iz tega dokumenta. Peltonove turbine, črpalke za shranjevanje in črpalno-turbinske enote niso zajete v tej prvi izdaji, čeprav je več tem relevantnih za te vrste hidravličnih strojev. Posebnosti in uporabnost za Peltonove turbine in črpalno-turbinske enote bodo obravnavane v kasnejši reviziji standarda.
Ta dokument opisuje metodologije za izvedbo ocene utrujenosti rotorjev turbin. Vključuje več ključnih vidikov, kot so določanje obremenitvenih dogodkov, ki jih je treba upoštevati med oceno, določanje napetosti za vsak od teh obremenitvenih dogodkov, ter podrobne pristope za ocenjevanje utrujenosti novih in obstoječih rotorjev. Poleg tega vključuje zahteve za proizvodnjo in zagotavljanje kakovosti, ki jih je treba upoštevati za dosego želenih lastnosti utrujenosti materiala in učinkovito uporabo predlaganih metodologij ocene utrujenosti. Dokument vsebuje tudi najboljše prakse za izvajanje in analizo meritev z merilnimi trakovi (strain gauge) na obstoječih rotorjih za oceno njihove življenjske dobe utrujenosti.
Namen tega dokumenta je zagotoviti smernice za oceno utrujenosti novih in obstoječih rotorjev turbin. Ne določa, ali je treba za določen rotor izvesti oceno utrujenosti ali ne. Vendar pa Priloga B nudi smernice za oceno potrebe po izvedbi ocene utrujenosti za določen nov rotor. Metode, opisane v tem dokumentu, se lahko uporabljajo tudi za ocene preostale življenjske dobe rotorjev v uporabi. Vendar je pomembno upoštevati, da se lahko lastnosti utrujenosti materialov ocenjenih rotorjev in raven kakovosti razlikujejo od predpisov, navedenih v oddelku za proizvodnjo in zagotavljanje kakovosti tega dokumenta, ki so bili določeni za nove rotorje. Prav tako je pomembno omeniti, da sama ocena utrujenosti ni zadostna za popolno validacijo mehanske celovitosti nove zasnove rotorja. Običajno se izvajajo tudi druge mehanske validacije, ki niso zajete v tem dokumentu.

General Information

• Status: Published
• Public Enquiry End Date: 31-May-2025
• Publication Date: 06-Jul-2026
• ICS: 27.140 - Hydraulic energy engineering
• Technical Committee: IEHT - Electrotechnics - Hydraulic turbins
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 07-Jul-2026
• Due Date: 11-Sep-2026
• Completion Date: 07-Jul-2026
• Ref Project: EN IEC 63230:2026 - Fatigue assessment of hydraulic turbine runners: from design to quality assurance

Relations

• Refers: SIST EN IEC 60193:2019 - Hydraulic turbines, storage pumps and pump-turbines - Model acceptance tests (IEC 60193:2019)
• Effective Date: 16-Jun-2026

Overview

SIST EN IEC 63230:2026 - Fatigue Assessment of Hydraulic Turbine Runners: From Design to Quality Assurance provides a comprehensive international standard for evaluating the fatigue life of hydraulic turbine runners. Developed by SIST and part of European and international standardization efforts, this document is crucial for owners, designers, and manufacturers of reaction turbines-such as Francis, Kaplan, propeller, and diagonal turbines-regardless of their size or configuration. The standard defines methodologies for fatigue assessment, focusing on ensuring mechanical integrity, optimizing runner performance, and supporting robust manufacturing and quality assurance processes within the scope of hydraulic energy engineering.

Key Topics

• Scope of Application

  • Applies to runners of reaction turbines (Francis, Kaplan, propeller, diagonal) in all configurations and sizes.
  • Excludes the internal mechanical components of blade adjustment mechanisms, Pelton turbines, storage pumps, and pump-turbines in this edition.

• Fatigue Assessment Methodologies

  • Outlines systematic approaches for identifying load events and performing fatigue analysis on both new and existing turbine runners.
  • Provides requirements for stress history evaluation from expected load events, including steady-state and transient operating conditions.

• Fatigue Life Assessment

  • Addresses methods and best practices for applying strain gauge measurements on-site to assess the remaining life of in-service runners.
  • Covers both S-N curve assessment (stress versus number of cycles) and fracture mechanics assessment for comprehensive fatigue analysis.

• Manufacturing and Quality Assurance

  • Specifies manufacturing requirements and quality assurance protocols designed to achieve targeted material fatigue properties.
  • Includes guidance for defect management, non-destructive testing (NDT), welding practices, post-weld heat treatment, and corrosion protection.

• Documentation and Decision Guidance

  • Provides guidance (Annex B) for determining when a fatigue assessment is necessary for a new runner.
  • Notes that fatigue analysis should be integrated with other mechanical validation activities for full structural integrity assessment.

Applications

• Design of New Hydraulic Turbine Runners

  • Supports designers in evaluating expected operational loads and specifying material and manufacturing requirements for new turbine runners.
  • Helps in defining fatigue-related criteria during the initial design phase, contributing to safer and more reliable hydropower systems.

• Assessment of Existing and In-service Runners

  • Offers owners and engineers a framework for evaluating the remaining operational life of existing runners using both historical operational data and field strain measurements.
  • Facilitates decision-making regarding runner refurbishment, replacement, and maintenance scheduling.

• Manufacturing and Supplier Compliance

  • Assists manufacturers and suppliers in implementing internationally recognized quality assurance measures to ensure runner durability.
  • Sets clear manufacturing tolerances and acceptance criteria for key processes, reducing the risk of fatigue-related failures over the runner's service life.

• Hydropower Plant Operations and Maintenance

  • Helps plant operators optimize maintenance schedules and operational strategies to extend runner life and improve power plant availability.

Related Standards

• IEC 60193:2019 - Hydraulic turbines, storage pumps and pump-turbines - Model acceptance tests
• BS 7910:2019 - Guide to methods for assessing the acceptability of flaws in metallic structures
• CCH 70-4 - Specification for Inspection of Steel Castings for Hydraulic Machines
• ISO 80000-4:2019 - Quantities and units Part 4: Mechanics
• ISO 21920-2:2021 - Geometrical product specifications (GPS) - Surface texture: Profile method

For organizations committed to hydraulic energy engineering and ensuring compliance with leading hydraulic turbine standards, SIST EN IEC 63230:2026 delivers a technical, practical framework for fatigue assessment and quality assurance-driving safety, efficiency, and reliability in hydropower applications.

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2026
Ocena utrujenosti tekačev hidravlične turbine: od načrtovanja do zagotavljanja
kakovosti (IEC 63230:2026)
Fatigue assessment of hydraulic turbine runners: from design to quality assurance (IEC
63230:2026)
Lebensdauerbewertung von Laufrädern hydraulischer Turbinen: vom Design bis zur
Qualitätssicherung (IEC 63230:2026)
Évaluation de la fatigue des roues de turbines hydrauliques: de la conception à
l'assurance qualité (IEC 63230:2026)
Ta slovenski standard je istoveten z: EN IEC 63230:2026
ICS:
27.140 Vodna energija Hydraulic energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 63230

NORME EUROPÉENNE
EUROPÄISCHE NORM July 2026
ICS 27.140
English Version
Fatigue assessment of hydraulic turbine runners: from design to
quality assurance
(IEC 63230:2026)
Évaluation de la fatigue des roues de turbines hydrauliques: Lebensdauerbewertung von Laufrädern hydraulischer
de la conception à l'assurance qualité Turbinen: vom Design bis zur Qualitätssicherung(IEC
(IEC 63230:2026) 63230:2026)
This European Standard was approved by CENELEC on 2026-06-11. CENELEC 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-CENELEC
Management Centre or to any CENELEC 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 CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 63230:2026 E
European foreword
The text of document 4/544/FDIS, future edition 1 of IEC 63230, prepared by TC 4 "Hydraulic turbines"
was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-07-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-07-31
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 63230:2026 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
ISO 80000-4:2019 NOTE Approved as EN ISO 80000-4:2019 (not modified)
IEC 60994:1991 NOTE Approved as EN 60994:1992 (not modified)
ISO 21920-2:2021 NOTE Approved as EN ISO 21920-2:2022 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60193 2019 Hydraulic turbines, storage pumps and EN IEC 60193 2019
pump-turbines - Model acceptance tests
BS 7910 2019 Guide to methods for assessing the - -
acceptability of flaws in metallic structures
CCH 70-4 Specification for Inspection of Steel - -
Castings for Hydraulic Machines

IEC 63230 ®
Edition 1.0 2026-05
INTERNATIONAL
STANDARD
Fatigue assessment of hydraulic turbine runners: from design to quality
assurance
ICS 27.140  ISBN 978-2-8327-1164-4

IEC 63230:2026-05(en)
IEC 63230:2026 © IEC 2026
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions, symbols and units . 6
3.1 General . 6
3.2 General terms and definitions . 6
3.3 Units . 10
3.4 Acronyms . 11
3.5 Subjective terms . 11
4 Stress history from expected load events . 11
4.1 Purpose and scope . 11
4.2 Load events . 11
4.3 Stress history and stress spectrum . 13
4.4 Stresses determined by calculation . 14
4.4.1 Stresses in steady state conditions . 14
4.4.2 Stresses in transient conditions . 18
4.5 Stresses determined from on-site strain measurements . 18
4.5.1 General. 18
4.5.2 Test procedure . 19
4.5.3 Instrumentation, acquisition and signal treatment . 19
4.5.4 Hotspot stress history determination . 19
5 Fatigue life assessment . 21
5.1 Purpose and scope . 21
5.2 S-N curve assessment . 22
5.2.1 Design S-N curve . 22
5.2.2 Mean stress effect. 23
5.2.3 Residual stress . 24
5.2.4 Cumulated damage calculation . 24
5.3 Fracture mechanics assessment . 25
5.3.1 General. 25
5.3.2 Loading conditions . 25
5.3.3 Fatigue crack growth law . 26
5.3.4 Fatigue crack growth threshold . 27
5.3.5 Definition of flaw . 28
5.3.6 Recommended crack growth limit for calculations . 28
5.3.7 Stress intensity factor solution . 29
6 Manufacturing and quality assurance . 29
6.1 Purpose . 29
6.2 Engineering instruction for manufacturing. 30
6.2.1 Designer responsibilities . 30
6.2.2 Hotspot area definition . 30
6.3 Quality management . 32
6.4 Manufacturing requirements. 32
6.4.1 Material properties . 32
6.4.2 Welding . 32
6.4.3 Defects removal . 33
IEC 63230:2026 © IEC 2026
6.4.4 Post-weld heat treatment . 34
6.4.5 Non-destructive testing (NDT) . 34
6.4.6 Corrosion protection . 36
6.4.7 Manufacturing tolerances . 36
Annex A (informative) Finite element analysis best practices . 37
Annex B (informative) Guidance on the necessity of conducting a fatigue assessment . 39
B.1 General . 39
B.2 Suggested characteristic of runners for which a fatigue assessment is not
required . 39
B.3 Suggested requirements and allowable stresses when fatigue assessment is
not required . 40
Bibliography . 41

Figure 1 – Constant amplitude loading illustration of the main fatigue stress
parameters . 10
Figure 2 – Example of load events included in a start-stop sequence . 13
Figure 3 – Example of a Francis runner strain measurement history during a start-stop
sequence with multiple power outputs [1] . 13
Figure 4 – Stochastic stress history of a steady state condition . 16
Figure 5 – Standard normalized stochastic stress spectrum curve and stress spectra
from real strain gauge data from which it was defined . 17
Figure 6 – Stress spectra combination method for stochastic stresses and periodic
stresses originating from (a) RSI and (b) part-load vortex rope . 18
Figure 7 – Schematic representation of (a) the localisation of strain gauges, (b) the
predicted strain pattern and (c) the superposition of the strain gauges within the
predicted strain pattern [9]. 20
Figure 8 – Example of a goodness-of-fit representation between measurement and
simulation results . 21
Figure 9 – Design S-N curve for 13 %Cr-4 %Ni stainless steel in river water at R = -1
(see 4.3 for stress amplitude calculation) . 23
Figure 10 – Illustration of the effect of the modified Goodman's model on the design S-
N curve for various mean stress values. 24
Figure 11 – Creation of the design fatigue life load history based on typical 1-year load
histories from assembled load sequences for fracture mechanics assessments . 26
Figure 12 – Standardized crack propagation curves for 13 %Cr-4 %Ni stainless steel
according to Equation (5) . 27
Figure 13 – Definition of recommended initial flaw shapes for a) surface flaws b)
embedded flaws . 28
Figure 14 – Location and definition of hotspot areas on a Francis runner . 31
Figure 15 – Location and definition of hotspot areas on a Kaplan runner blade . 31

Table 1 – Example of specified expected steady state conditions . 12
Table 2 – Example of specified expected transient conditions . 12
Table 3 – Main sources of runner excitation . 14
Table 4 – Design S-N curve coefficients for 13%Cr-4%Ni stainless steels in river water . 22
Table 5 – Parameters of the 13 %Cr-4 %Ni fatigue crack growth law . 27
Table 6 – Recommended PWHT parameters for runners. 34
Table 7 – Acceptance criteria for non-destructive tests on surface excavations, finished
hotspot areas weld reworks and finished hotspot areas . 36
IEC 63230:2026 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Fatigue assessment of hydraulic turbine runners:
from design to quality assurance

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 63230 has been prepared by IEC technical committee TC 4: Hydraulic turbines. It is an
International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
4/544/FDIS 4/552/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
IEC 63230:2026 © IEC 2026
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC 63230:2026 © IEC 2026
1 Scope
This International Standard applies to runners of reaction turbines, regardless of their size and
capacity. These can include radial turbines such as Francis turbines, axial turbines such as
Kaplan and propeller turbines, as well as diagonal turbines, in all possible configurations. In the
case of turbine runners with adjustable blades, the internal mechanical components of the
blades' adjustment mechanism are excluded from this document. Pelton turbines, storage
pumps and pump-turbines are not covered in this first edition, even though several topics are
applicable to these types of hydraulic machines. Specificities and applicability to Pelton turbine
and pump-turbines will be discussed in a later revision of the standard
This document outlines the methodologies for conducting a fatigue assessment of turbine
runners. It encompasses several key aspects, such as defining the load events to be considered
during the assessment, determining stresses for each of these load events, as well as the
detailed approaches for assessing fatigue of new and existing runners. Additionally, it includes
manufacturing and quality assurance requirements to be complied with to achieve the desired
material fatigue properties and effectively apply the proposed fatigue assessment
methodologies. This document also contains best practices for performing and analysing on-
site strain gauge measurements performed on existing runners to evaluate their fatigue life.
The purpose of this document is to provide guidelines to assess fatigue in new and existing
turbine runners. It does not specify if a fatigue assessment should be performed or not for a
given runner. However, Annex B provides guidance to evaluate the necessity of realizing a
fatigue assessment or not for a given new runner. The methods described in this document can
also be used for remaining life assessments of in-service runners. However, it is important to
consider that the assessed runner materials' fatigue properties and quality level could differ
from the prescriptions found in the manufacturing and quality assurance section of this
document which have been defined for new runners. It is also important to mention that fatigue
assessment alone is not sufficient for a complete validation of the mechanical integrity of a new
runner design. Other mechanical validations not covered in this document are typically
conducted.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC 60193:2019, Hydraulic turbines, storage pumps and pump-turbines - Model acceptance
tests
BS 7910:2019, Guide to methods for assessing the acceptability of flaws in metallic structures
CCH 70-4, Specification for Inspection of Steel Castings for Hydraulic Machines
IEC 63230:2026 © IEC 2026
3 Terms, definitions, symbols and units
3.1 General
For the purposes of this document, the following terms, definitions, symbols and units apply.
NOTE Specialized terms are explained where they appear. Where terms are not explicitly defined in this document,
the terms and definitions of IEC TR 61364[1] , as well as those of ASTM E1823-21[2] can be considered where
applicable.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.2 General terms and definitions
The terms below are defined specifically in the context of this document. The provided
definitions may not be complete or coherent with definitions from other standards and codes.
3.2.1
continuous normal operating range
operating range of the turbine for unrestricted operating duration, typically delimited by
minimum and maximum values of net head, minimum values of net positive suction energy, as
well as minimum and maximum values of either or a combination of flow, turbine power output
and guide vane opening
3.2.2
cycle counting method
method of counting the number of discrete stress (strain) cycles of different amplitude and mean
from a history of varying stress (strain)
3.2.3
design fatigue life
the minimum period of time during which the runner is expected to function, according to its
corresponding stress history
3.2.4
design S-N curve
S-N curve defined for design purposes of specific components
Note 1 to entry: It includes sufficient reduction coefficients to ensure conservative results and corresponds to what
is considered a sufficient level of reliability for its related specific components. As the determination of this curve
includes the return of experience on past runners, it cannot be associated with specific levels of probability of
survival.
3.2.5
designer
entity responsible for analysing and translating technical specifications into design solutions
that have the required reliability, safety, integrity and performance levels
3.2.6
dynamic stress
variation of stress over time around a mean stress
___________
Numbers in square brackets refer to the Bibliography.
IEC 63230:2026 © IEC 2026
3.2.7
fatigue crack initiation
fatigue phase during which damage is accumulated in a runner under the action of stress cycles
Note 1 to entry: In the context of a fatigue crack initiation assessment as part of this document, the runner material
is considered to be continuous, and stress is determined according to the principles of continuum mechanics.
3.2.8
fatigue crack propagation
fatigue phase during which a crack propagates in a runner under the action of stress cycles
Note 1 to entry: In the context of a fatigue crack propagation assessment as part this document, the runner material
is considered to contain a discontinuity and stress is determined according to the principles of fracture mechanics.
3.2.9
hotspot
location on the runner with the highest fatigue damage sums for a given stress history
Note 1 to entry: This normally corresponds to the location of the highest dynamic stress during steady state
conditions or the highest stress range of the start-stop sequence.
3.2.10
load event
loading applied to the runner during a specific steady state or transient condition (e.g. start-up,
speed-no-load)
3.2.11
load rejection
transient operating condition characterized by an emergency automatic sequence where
sudden decoupling from the grid and subsequent closing of the guide vanes result in a turbine-
generator unit going from a given power output to transient overspeed and back to speed-no-
load or standstill
3.2.12
load sequence
series of load events, which can include a combination of steady state and transient conditions,
that are frequently repeated (e.g. start-stop load sequence: standstill – start-up - SNL- ramp-
up - full load – stop – standstill)
3.2.13
manufacturer
entity responsible for carrying out the entire manufacturing process until completion of the
hydraulic machine component
3.2.14
maximum power output
highest turbine or unit power output within the continuous normal operating range under a given
net head
3.2.15
mean stress
constant average stress of a steady state condition or moving average stress of a transient
stress history
Note 1 to entry: This term can also refer to the mean stress of a single fatigue cycle from a stress spectrum as
obtained from a cycle counting algorithm.
3.2.16
owner
entity which is either the buyer or user, or both, of the hydraulic machine component, or its
representative
IEC 63230:2026 © IEC 2026
3.2.17
periodic stress
dynamic stress of constant amplitude and frequency
3.2.18
rainflow algorithm
specific cycle counting method used in this document
Note 1 to entry: In this document, rainflow refers to the method named "simplified rainflow counting for repeating
Histories" as per ASTM E1049-85.
3.2.19
residual stress
internal stress in static equilibrium that remains in the absence of any external loading
Note 1 to entry: In runners, such residual stresses most often stem from welding, casting, machining and forming.
3.2.20
rework
process of correcting defective, failed, or non-conforming features in a prototype runner after
inspection
Note 1 to entry: In the context of this document, this process can include weld repair, machining, grinding and
polishing.
3.2.21
runaway
no-load and non-excited steady state operating condition where a turbine-generator unit is
rotating at its maximum runaway speed achieved with guide vanes fully open, under the
maximum net head of the continuous operating range, or whichever condition results in the
highest rotational speed
3.2.22
shutdown
transient operating condition characterized by a normal automatic sequence where a turbine-
generator unit goes from a given power output to standstill
3.2.23
speed-no-load
no-load steady state operating condition where a turbine-generator unit is rotating at
synchronous speed, ready to be synchronized with the grid with positive speed direction and
zero power output
Note 1 to entry: The generator field winding can be excited or not.
3.2.24
start-up
transient operating condition characterized by a normal automatic sequence where a turbine-
generator unit goes from standstill with guide vanes closed to speed-no-load
3.2.25
static stress
constant mean stress, linearized or not, calculated by static structural finite element analysis
for a given steady state condition
IEC 63230:2026 © IEC 2026
3.2.26
steady state conditions
operating condition of the turbine characterised by constant (or almost constant) values of net
head, turbine power output, net positive suction head and rotational speed
Note 1 to entry: Runner mean stresses and characteristics of runner dynamic stresses (amplitude, range, frequency
spectrum, standard deviation, etc.) remain constant for a given steady state condition.
3.2.27
stochastic stress
dynamic stress of randomly varying amplitudes and wideband frequency contents
3.2.28
stress amplitude
one half of the stress range of a cycle (see Figure 1)
3.2.29
stress cycle
variation of stress at a particular point in the runner as obtained from a cycle counting method
and consisting of a change in stress between defined minimum (valley) and maximum (peak)
values and back again
3.2.30
stress history
record or calculation of the stress over time at a particular point in the runner during a load
event or during one or successive load sequences
3.2.31
strain history
record or calculation of the strain over time at a particular point in the runner during a load
event or during one or successive load sequences
3.2.32
stress range
algebraic difference between successive peak and valley stress (see Figure 1)
Note 1 to entry: In constant amplitude loading (see Figure 1), the range is given as follows:
∆S S− S .
max min
3.2.33
stress ratio
algebraic ratio of the lowest algebraic value of an applied stress cycle (S ) and the highest
min
algebraic value of applied stress load in a cycle (S ) (see Figure 1)
max
=
IEC 63230:2026 © IEC 2026
Figure 1 – Constant amplitude loading illustration of the main fatigue stress parameters
3.2.34
stress spectrum
tabulation of the number of all discrete stress cycles of a given amplitude and mean stress
level, as obtained from the rainflow algorithm applied to a stress history
3.2.35
supplier
entity responsible for supplying to the owner the equipment in conformity with contractual
specifications
3.2.36
temporary operating range
operating range of the turbine outside the continuous normal operating range subject to a
specified allowed maximum number of yearly operating hours
3.2.37
transient condition
fast or slow transition from one steady state condition to another (including standstill)
Note 1 to entry: Runner mean stress and characteristics of runner dynamic stresses (amplitude, range, frequency
spectrum, standard deviation, etc.) vary during a given transient condition.
3.3 Units
The International System of Units (SI, see ISO 80000-4[3]) has been used throughout this
document.
All terms are given in SI base units or derived coherent units. The basic equations are valid
using these units. This is taken into account if other than coherent SI units are used for certain
data (e.g. kilowatt instead of watt for power, kilopascal or bar instead of pascal for pressure,
min-1 instead of s-1 for rotational speed, etc.). Temperatures can be given in degrees Celsius
since absolute temperatures (in kelvins) are rarely required.
Any other system of units can be used if agreed in writing by the contracting parties.
IEC 63230:2026 © IEC 2026
3.4 Acronyms
Below is a list of acronyms used throughout the document.
BHN Brinell hardness number
CFD Computational fluid dynamics
FEA Finite element analysis
FEM Finite element method
NDT Non-destructive testing
PWHT Post-weld heat treatment
RSI Rotor-stator interaction
SNL Speed-no-load
3.5 Subjective terms
Some terms used in this document can have a subjective interpretation, e.g. suitable, adequate,
sufficient, significant. This can lead to discussions between owners and suppliers. To provide
a degree of objectivity to these terms, the level of accuracy of the related assessment shall be
considered. Any method, measurement, analysis, simulation, etc. can be considered suitable,
appropriate, adequate, sufficient, significant, etc., as long as it is consistent with the precision
of the overall assessment and does not increase the level of uncertainty by itself.
This also applies if the supplier proposes alternative methods, in which case the supplier shall
demonstrate to the owner that the accuracy achieved by the proposed alternative method is
equal to or better than the methods described in this document. The supplier shall provide
documentation to support the alternative method such as internal or public documentation
reviewed by independent peers comparing the proposed alternative methods with relevant
benchmarks. The owner shall evaluate the information provided and decide whether to accept
the method, failing which the original method shall be used.
4 Stress history from expected load events
4.1 Purpose and scope
Clause 4 provides general information on load events and related stresses that shall be
considered as part of a fatigue assessment of a runner. Its main purposes are:
– to provide guidance on operating conditions to be considered and the definition of related
load events required for runner fatigue assessment;
– to define the characteristic of fatigue-relevant loads and stresses to which runners can be
subject;
– to provide a general discussion on how stresses related to specific load events and
sequences can be predicted or calculated.
4.2 Load events
The definition of load events for the fatigue assessment of a runner shall be established on a
case-by-case basis depending on the expected operating regime of the turbine. The expected
type, range, frequency and number of load events, as well as the required design fatigue life,
shall be specified by the owner.
For the design of new runners, or residual life assessment of existing runners, owners shall
specify the steady state conditions under which the turbine is expected to be operated.
IEC 63230:2026 © IEC 2026
These steady state conditions should typically be specified in terms of yearly hours of operation
in a similar manner as shown in Table 1. This should include operation at each specified steady
state condition for the rated net head, as well for the minimum, maximum and any other relevant
net heads in the case of a large net head range. The power or flow ranges shown in Table 1
represent one example and can be modified by the owner to suit the expected operation of the
specified runner.
The specified yearly hours of operation within power or flow ranges outside typical normal
operating ranges (e.g. below 60 % to 70 % of the maximum power in the case of a Francis
runner) shall be as realistically defined as possible to avoid unnecessary constraints on the
design which can lead to compromise on efficiency and on cavitation behaviour.
Table 1 – Example of specified expected steady state conditions
Power or flow range (%) Power [MW] Number of Number of …
hours per year hours per year
or flow [m /s]
for head ___m for head ___m
range
High load temporary operating range
90 % to 100 %
70 % to 90 %
40 % to 70 %
10 % to 40 %
Low load temporary operating range
Speed-no-load
Other steady-state conditions
In addition to steady state conditions, owners shall also specify all transient conditions that the
runner can realistically see during its lifetime, along with the expected number of events for
each transient condition, which can be in terms of number of occurrences per year or for the
entire design fatigue life, in a manner similar to Table 2 below.
Table 2 – Example of specified expected transient conditions
Transient condition Number of events
(per year or per entire design fatigue life)
Start-ups and shutdowns
Load rejections
Speed ramp-up to runaway
Power variations
from ___MW to ___MW (or in % of maximum power)
from ___MW to ___MW
from ___MW to ___MW
Synchronous condenser transitions
Ancillary services relevant for fatigue
(e.g. frequency control, load control, black starts)

In addition, for the assessment of existing runners, the owner should provide historical
operational data since the runner's commissioning, information on on-site repairs and
modifications, all available hydraulic performance data, as well as all relevant test data to
establish the actual hydraulic conditions under which the runner was operated.
IEC 63230:2026 © IEC 2026
4.3 Stress history and stress spectrum
In order to define the stress history for a runner, the designer shall create sequences of
transient and steady state load events to represent the expected runner operation. Each
sequence shall begin and end at the same condition, thus representing a complete cycle. The
creation of such representative load sequences, as opposed to using only the separate load
events part of the sequence, is required as the resulting stress history can result in a larger
cycle envelope.
With such an established stress history, a stress spectrum can be obtained by applying a cycle
counting method to the entire stress history. The technicalities of various cycle counting
methods to be used in fatigue analysis are explained in ASTM E1049-85. In the context of this
document, the simplified rainflow counting method as described in ASTM E1049 is
recommended.
Figure 2 shows an example of a schematic representation of such a load sequence, while
Figure 3 presents an example of a strain measurement illustrating the strain history of a stop-
start-power-stop sequence.
Figure 2 – Example of load events included in a start-stop sequence

Figure 3 – Example of a Francis runner strain measurement history
during a start-stop sequence with multiple power outputs [1]
For FEA stress evaluation, stress amplitude and mean stress values of the different stress
cycles included in the stress spectrum shall be derived from the complete stress tensor using
standardized methods detailed in well-known codes (e.g. [4], [5]). For instance, for S-N curve
analysis, the equivalent Von Mises stress of the resulting tensor can be used, and for crack
propagation analysis, the maximum principal stress of the resulting tensor can be used.
IEC 63230:2026 © IEC 2026
4.4 Stresses determined by calculation
4.4.1 Stresses in steady state conditions
4.4.1.1 General
Stresses in the runner during steady state conditions can include static stresses, dynamic
stresses, or a combination of both.
4.4.1.2 Static stresses
Static stresses in runners under steady state conditions are typically calculated by FEA using
a linear elastic model of strain-stress correlation.
The specific load cases to be considered for the calculation will vary on a case-by-case basis
depending on the operating regime and expected load events of a given runner. At a minimum,
static stresses should be calculated for the following load events:
– speed-no-load;
– maximum flow or maximum power output condition, whichever results in the most
unfavourable static stresses in each assessed hotspot of the runner. This shall consider the
high load temporary operating range if applicable;
– maximum theoretical runaway speed.
Prediction of static stresses in these steady state conditions using FEA is a well-established
method that has been shown, through strain gauge testing, to accurately predict static stresses
in the runner. Annex A provides guidelines on best practices for static structural FEA of turbine
runners.
4.4.1.3 Dynamic stresses
4.4.1.3.1 General
Dynamic stresses occurring in runners during operation at steady state conditions typically
include periodic stresses, stochastic stresses, or a superposition of both.
Periodic stresses are caused by hydraulic phenomena acting as sources of excitation. Such
exciting phenomena can be amplified by resonance conditions when external excitation
frequencies under specific nodal diameters coincide with one or more of the runner's natural
frequencies of the same nodal diameter.
On the other hand, stochastic stresses are typically of a random and irregular nature and cannot
be associated with specific frequencies.
Potential sources of excitation which should be considered are shown in Table 3.
Table 3 – Main sources of runner excitation
Type of excitation source Characteristic
Rotor stator interaction (RSI) Periodic
Draft tube vortex Periodic
Von Karman vortices Periodic
Inter blade vortices Stochastic
Vaneless space vortices Stochastic

IEC 63230:2026 © IEC 2026
In addition to assessing static stresses, the runner designer or supplier should assess dynamic
stresses in relevant steady state conditions, covering the entire operating range, either by
predicting the stresses themselves or providing justification to demonstrate that the periodic
and stochastic stresses can be neglected. Such stress predictions and justifications can be
based on reference stress measurements or calculations from similar runners.
4.4.1.3.2 Perio
...