Proof of competence of hydraulic cylinders in crane applications

This document applies to hydraulic cylinders that are part of the load carrying structure of cranes. It is intended to be used together with the ISO 8686 series and ISO 20332, and as such they specify general conditions, requirements and methods to prevent mechanical hazards of hydraulic cylinders, by design and theoretical verification. This document does not apply to hydraulic piping, hoses, connectors and valves used with the cylinders, or cylinders made from other material than (carbon) steel.

Vérification d’aptitude des vérins hydrauliques pour appareils de levage

General Information

Status
Published
Publication Date
14-Sep-2022
Current Stage
6060 - International Standard published
Due Date
08-Dec-2022
Completion Date
15-Sep-2022
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INTERNATIONAL ISO
STANDARD 23778
First edition
2022-09
Proof of competence of hydraulic
cylinders in crane applications
Vérification d’aptitude des vérins hydrauliques pour appareils de
levage
Reference number
ISO 23778:2022(E)
© ISO 2022
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ISO 23778:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
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ISO 23778:2022(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 2

5 General ........................................................................................................................................................................................................................... 3

5.1 Documentation ....................................................................................................................................................................................... 3

5.2 Materials for hydraulic cylinders ........................................................................................................................................... 5

5.2.1 General requirements .................................................................................................................................................... 5

5.2.2 Grades and qualities ........................................................................................................................................................ 6

6 Proof of static strength .................................................................................................................................................................................7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Limit design stresses ........................................................................................................................................................................ 8

6.2.1 General ........................................................................................................................................................................................ 8

6.2.2 Limit design stress in structural members ................................................................................................ 8

6.2.3 Limit design stresses in welded connections ........................................................................................... 9

6.3 Linear stress analysis ....................................................................................................................................................................... 9

6.3.1 General ........................................................................................................................................................................................ 9

6.3.2 Typical cylinder arrangements.............................................................................................................................. 9

6.3.3 Cylinder tube....................................................................................................................................................................... 11

6.3.4 Cylinder bottom ...............................................................................................................................................................13

6.3.5 Piston rod welds .............................................................................................................................................................. 14

6.3.6 Cylinder tube and piston rod threads .......................................................................................................... 14

6.3.7 Thread undercuts and locking wire grooves ......................................................................................... 14

6.3.8 Oil connector welds ...................................................................................................................................................... 15

6.3.9 Connecting interfaces to crane structure ................................................................................................. 16

6.4 Nonlinear stress analysis ........................................................................................................................................................... 16

6.4.1 General ..................................................................................................................................................................................... 16

6.4.2 Standard cylinder with end moments .......................................................................................................... 16

6.4.3 Support leg ............................................................................................................................................................................ 16

6.5 Execution of the proof ................................................................................................................................................................... 17

6.5.1 Proof for load bearing components ................................................................................................................ 17

6.5.2 Proof for bolted connections ................................................................................................................................ 17

6.5.3 Proof for welded connections .............................................................................................................................. 18

7 Proof of fatigue strength ..........................................................................................................................................................................18

7.1 General ........................................................................................................................................................................................................ 18

7.2 Stress histories .................................................................................................................................................................................... 18

7.3 Execution of the proof ................................................................................................................................................................... 20

7.4 Limit design stress range ........................................................................................................................................................... 20

7.5 Details for consideration ............................................................................................................................................................20

7.5.1 General .....................................................................................................................................................................................20

7.5.2 Bottom weld ........................................................................................................................................................................ 20

7.5.3 Notch stress at oil connectors ............................................................................................................................. 23

7.5.4 Cylinder head ...................................................................................................................................................................... 24

7.5.5 Piston rod .............................................................................................................................................................................. 26

7.5.6 Cylinder head bolts ........................................................................................................................................................28

7.5.7 Cylinder head flange weld .......................................................................................................................................28

7.5.8 Mechanical interfaces ................................................................................................................................................. 30

8 Proof of elastic stability ............................................................................................................................................................................30

8.1 General ........................................................................................................................................................................................................30

8.2 Critical buckling load .....................................................................................................................................................................30

8.3 Limit compressive design force ............................................................................................................................................ 32

iii
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ISO 23778:2022(E)

8.4 Execution of the proof ................................................................................................................................................................... 33

Annex A (informative) Critical buckling load for common buckling cases .............................................................34

Annex B (informative) Second order analysis of two important cases........................................................................38

Annex C (informative) Shell section forces and moments for cylinder bottom ..................................................41

Annex D (informative) Fatigue analysis of bottom weld for more complex cases .......................................... 44

Bibliography .............................................................................................................................................................................................................................47

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ISO 23778:2022(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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 96, Cranes, Subcommittee SC 10, Design

principles and requirements.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
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INTERNATIONAL STANDARD ISO 23778:2022(E)
Proof of competence of hydraulic cylinders in crane
applications
1 Scope

This document applies to hydraulic cylinders that are part of the load carrying structure of cranes. It is

intended to be used together with the ISO 8686 series and ISO 20332, and as such they specify general

conditions, requirements and methods to prevent mechanical hazards of hydraulic cylinders, by design

and theoretical verification.

This document does not apply to hydraulic piping, hoses, connectors and valves used with the cylinders,

or cylinders made from other material than (carbon) steel.
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.

ISO 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method

ISO 683-1, Heat-treatable steels, alloy steels and free-cutting steels — Part 1: Non-alloy steels for quenching

and tempering·

ISO 683-2, Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and

tempering
ISO 724, ISO general-purpose metric screw threads — Basic dimensions

ISO 5817:2014, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding

excluded) — Quality levels for imperfections
ISO 8492, Metallic materials — Tube — Flattening test
ISO 8686 (all parts), Cranes — Design principles for loads and load combinations

ISO 12100, Safety of machinery — General principles for design — Risk assessment and risk reduction

ISO 20332:2016, Cranes — Proof of competence of steel structures

EN 10277:2018, Bright steel products — Technical delivery conditions — Part 2: Steels for general

engineering purposes

EN 10297-1, Seamless circular steel tubes for mechanical and general engineering purposes — Technical

delivery conditions — Part 1: Non-alloy and alloy steel tubes

EN 10305-1, Steel tubes for precision applications — Technical delivery conditions — Part 1: Seamless cold

drawn tubes

EN 10305-2, Steel tubes for precision applications — Technical delivery conditions — Part 2: Welded cold

drawn tubes
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 12100 apply.

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ISO 23778:2022(E)

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Symbols
For the purposes of this document, the symbols given in Table 1 apply.
Table 1 — Symbols
Symbols Description
A% Percentage elongation at fracture
a Weld throat thickness
A , B , C , D Constants
i i i i
A Stress area
D Piston diameter
d Rod diameter
D Axles diameter
a,i
D Pressure affected diameter
D Weld diameter
E Modulus of elasticity
F Compressive force
F Compressive force
FE Finite elements
f Limit design stress
f Limit design stress, normal
Rdσ
f Limit design stress, shear
Rdτ
F Lateral force
F External compressive design force
f Limit design weld stress
w,Rd
f Yield strength
h thickness of the cylinder bottom
I Moment of inertia, generic
I Moment of inertia of the tube
I Moment of inertia of the rod
L Overall length of the cylinder
L Length of the cylinder tube
L Length of the piston rod
m Slope of the log Δσ − log N curve

M Shell section bending moment, acting at the intersection between tube and bottom

M Bending moment
N Compressive force
N Critical buckling load
N Limit compressive design force
p Maximum pressure in piston side chamber
p Maximum pressure in rod side chamber
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ISO 23778:2022(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbols Description
p Outer pressure
p Design pressure
R Middle radius of the tube (R = r + t/2)
r Inner radius of the tube
r Outer radius of the tube
r Outer radius of the piston rod
s Stress history parameter (see ISO 20332)
t Wall thickness of the tube

T Shell section transverse force, acting at the intersection between tube and bottom

x, y Longitudinal and lateral coordinates
α Angular misalignment, radians
γ General resistance factor (γ = 1,1, see ISO 8686-1)
m m
γ Fatigue strength specific resistance factor (see ISO 20332)
γ Total resistance factor (γ = γ × γ )
R R m s
γ Specific resistance factor
Δσ Stress range
Δσ Bending stress range in the tube
Δσ Characteristic fatigue strength
Δσ Membrane stress range in the tube (axial)
Δσ Limit design stress range
Δσ Design stress range
Δp Design pressure range on piston side
δ Maximum displacement
max
κ Reduction factor for buckling
λ Slenderness
λ Friction parameters
μ Friction factors
ν Poisson’s ratio (ν = 0,3 for steel)
σ Axial stress in the tube
σ Lower extreme value of a stress range
σ Radial stress in the tube
σ Design stress, normal
σ Design weld stress, normal
w,Sd
σ Tangential stress in the tube (hoop stress)
σ Upper extreme value of a stress range
τ Design stress, shear
τ Design weld stress, shear
w,Sd
5 General
5.1 Documentation
The documentation of the proof of competence shall include:
— design assumptions including calculation models;
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ISO 23778:2022(E)
— applicable loads and load combinations;
— material grades and qualities;
— weld quality levels, in accordance with ISO 5817 and ISO 20332;
— relevant limit states;
— results of the proof of competence calculation, and tests when applicable.
The main parts of hydraulic cylinder are indicated in Figure 1 to Figure 3.
Key
1 bushing 8 piston
2 rod head 9 nut
3 cylinder head 10 cylinder bottom
4 oil connector 11 grease nipple
5 piston rod 12 piston side chamber
6 cylinder tube 13 rod side chamber
7 spacer
Figure 1 — Complete cylinder
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ISO 23778:2022(E)
Key
1 wiper
2 O-ring
3 secondary seal
4 guide ring (2 ×)
5 primary seal
6 backup ring
7 O-ring
Figure 2 — Cylinder head
Key
1 seal
2 pressure element
3 guide ring (2 ×)
Figure 3 — Piston
Figures 1 to 3 show some typical design features. Other designs may be used.
5.2 Materials for hydraulic cylinders
5.2.1 General requirements

The materials for load carrying cylinder tubes and piston rods shall fulfil the following requirements:

— The impact toughness in the transversal direction shall be tested in accordance with ISO 148-1

and shall meet the requirements stated in ISO 20332. Samples shall be cut out in the longitudinal

direction. For cylinder tubes and pressurized piston rods, samples shall also be cut out in the

transversal direction. The samples shall be prepared such that the axis of the notch is perpendicular

to the surface of the tube.
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ISO 23778:2022(E)
Key
1 sample cut out in longitudinal direction
2 sample cut out in transversal direction
Figure 4 — Sample for impact toughness testing

— If the material thickness does not allow samples to be cut out in the transversal direction, the tube

material shall pass a flattening test in accordance with ISO 8492. For welded tubes, two tests are

required; one with the weld aligned with the press direction and one where the weld is placed 90°

from the press direction, see Figure 4. The tube section shall be flattened down to a height H given

by:
10, 7⋅t
H =
C +
where
C is a factor that depends on the yield strength of the material,
C is 0,07 for f ≤ 400 MPa and C is 0,05 for f > 400 MPa;
y y
D is the outer diameter of the tube;
t is the wall thickness of the tube.
Material used in other parts shall meet the requirements specified in ISO 20332.
5.2.2 Grades and qualities

Steels in accordance with the following standards shall preferably be used as material for cylinder

tubes and piston rods:
— ISO 683-1;
— ISO 683-2;
— EN 10277:2018;
— EN 10297-1:
— EN 10305-1;
— EN 10305-2.
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ISO 23778:2022(E)

Alternatively, other steel grades and qualities than those listed in this subclause may be used as

material for cylinder tubes and piston rods, provided that the following conditions apply:

— the design value of f is limited to f /1,1 for materials with f /f < 1,1;
y u u y

— the percentage elongation at fracture A % ≥ 14 % on a gauge length LS=×56, 5 (where S is the

00 0
original cross-sectional area).

Grades and qualities of materials used in other parts of cylinders or mounting interfaces of cylinders

shall be selected in accordance with ISO 20332.
6 Proof of static strength
6.1 General

A proof of static strength by calculation is intended to prevent excessive deformations due to yielding

of the material, elastic instability and fracture of structural members or connections. Dynamic factors

given in the relevant part of ISO 8686 are used to produce equivalent static loads to simulate dynamic

effects. Also, load increasing effects due to deformation shall be considered. The theory of plasticity

for calculation of ultimate load bearing capacity is not considered acceptable for the purposes of this

document. The proof shall be carried out for structural members and connections while taking into

account the most unfavourable load effects from the load combinations A, B or C in accordance with the

relevant part of ISO 8686 or relevant product standards.

This document considers only nominal stresses, i.e. those calculated using traditional elastic strength

of materials theory; localized stress concentration effects are excluded. When alternative methods of

stress calculation are used such as finite element analysis, using those stresses directly for the proof

given in this document can yield inordinately conservative results as the given limit states are intended

to be used in conjunction with nominal stresses.

Cylinder actions are either active or passive. The action is active when the force from the cylinder exerts

a positive work on the crane structure, elsewise the action is passive.

As the forces applied to the cylinder by the crane structure are computed in accordance with ISO 8686,

they are already increased by the partial safety factors γ and relevant dynamic factors. Formula (1)

and Formula (2) give design pressures p caused by forces acting on the cylinder from the crane

structure. In addition, additional pressures p caused by internal phenomena in the hydraulic circuit

Sde

shall be considered and added to the design pressures p . Such internally generated pressures can be

caused, for example, by regenerative connections, pressure drop in return lines or cushioning.

In case a cylinder is intended to be tested as a component at higher pressure than the design pressure

p , this load case shall also be taken into account in the proof of static strength, and in which case the

test pressure shall be multiplied by a partial safety factor γ equal to 1,05.

The design pressure p in the piston side chamber or in the rod side chamber shall be computed from

the design force F taking into account the force direction and the cylinder efficiency η due to friction.

An efficiency factor Ψ is used to handle the effect of cylinder friction. For active cylinders Ψ has the

value of 1/η and for passive cylinders Ψ has the value of η.
For the piston side chamber, the design pressure is given by Formula (1):
4⋅F
p = ⋅Ψ (1)
π⋅D
where
F is the external design force;
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ISO 23778:2022(E)
D is the piston diameter;
Ψ is set to η for passive cylinders and to 1/η for active cylinders.
For the rod side chamber, the design pressure is given by Formula (2):
4⋅F
p = ⋅+Ψ p (2)
Sd Sde
π⋅−Dd
where
F is the external design force;
D is the piston diameter;
d is the rod diameter;
Ψ is set to η for passive cylinders and to 1/η for active cylinders;
p is additional pressure caused by internal phenomena (e.g. regeneration).
Sde

Unless justified value of the efficiency η is available and used, Ψ shall be assigned the value of 1,1 for

active cylinders and the value of 1,0 for passive cylinders.
6.2 Limit design stresses
6.2.1 General
The limit design stresses f shall be calculated from Formula (3):
ff= f ,γ (3)
Rd nk R
where
f is a general function as described in 6.2.2;
f is the characteristic values (or nominal value);
γ is the total resistance factor.
6.2.2 Limit design stress in structural members

The limit design stress f , used for the design of structural members, shall be calculated from

Formulae (4) and (5):
f = for normal stresses (4)
Rdσ
f = for shear stresses (5)
Rdτ
γ ⋅ 3
with γγ= · γ
Rm msm
where
f is the minimum value of the yield stress of the material;
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ISO 23778:2022(E)
is the general resistance factor γ =11, (see ISO 8686-1);
γ is the specific resistance factor for material in accordance with ISO 20332;

γ = 0,95 is the basic value for material not loaded perpendicular to the rolling plane.

For tensile stresses perpendicular to the plane of rolling (see Figure 5), the material shall be suitable for

carrying perpendicular loads and be free of lamellar defects. ISO 20332 specifies the values of γ for

material loaded perpendicular to the rolling plane.

Figure 5 provides an example of a cylinder tube bottom where plate steel is used (eye is welded) and

shows a tensile load perpendicular to plane of rolling.
Key
1 plane of rolling
2 direction of stress/load
Figure 5 — Tensile load perpendicular to plane of rolling
6.2.3 Limit design stresses in welded connections

The limit design weld stress f used for the design of a welded connection shall be in accordance with

w,Rd
ISO 20332.
6.3 Linear stress analysis
6.3.1 General

Subclause 6.3 comprises typical details for consideration that may be relevant for the proof of static

strength. Details that are only relevant for fatigue analysis (e.g shell bending of tube) are not dealt

with in 6.3. For cases or conditions not covered here, other recognized sources or static pressure/force

testing may be used.
6.3.2 Typical cylinder arrangements

Before executing calculations, boundary conditions and loading shall be investigated. Typical conditions

to be determined are:
— external forces and directions;
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ISO 23778:2022(E)
— type of cylinder;
— cylinder tube and rod mounting to the machine;
— forces/stresses due to thread pre-tightening;
— direction of gravity.

Different pressurized cylinder arrangements shall be considered when calculating static strength for

cylinders.
Typical pressurized cylinder arrangements are shown in Figure 6 to Figure 10.
Key
p pressure in piston side chamber
Figure 6 — Pushing cylinder with supported bottom
Key
p pressure in piston side chamber
Figure 7 — Pushing cylinder, flange mounted with unsupported bottom
Key
...

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