ISO 23778:2022

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)
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© ISO 2022
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Published in Switzerland
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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
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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.
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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
s
D Piston diameter
d Rod diameter
D Axles diameter
a,i
D Pressure affected diameter
p
D Weld diameter
w
E Modulus of elasticity
F Compressive force
F Compressive force
A
FE Finite elements
f Limit design stress
Rd
f Limit design stress, normal
Rdσ
f Limit design stress, shear
Rdτ
F Lateral force
S
F External compressive design force
Sd
f Limit design weld stress
w,Rd
f Yield strength
y
h thickness of the cylinder bottom
I Moment of inertia, generic
I Moment of inertia of the tube
1
I Moment of inertia of the rod
2
L Overall length of the cylinder
L Length of the cylinder tube
1
L Length of the piston rod
2
m Slope of the log Δσ − log N curve
M Shell section bending moment, acting at the intersection between tube and bottom
0
M Bending moment
b
N Compressive force
N Critical buckling load
k
N Limit compressive design force
Rd
p Maximum pressure in piston side chamber
i1
p Maximum pressure in rod side chamber
i2
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ISO 23778:2022(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbols Description
p Outer pressure
o
p Design pressure
Sd
R Middle radius of the tube (R = r + t/2)
i
r Inner radius of the tube
i
r Outer radius of the tube
o
r Outer radius of the piston rod
r
s Stress history parameter (see ISO 20332)
3
t Wall thickness of the tube
T Shell section transverse force, acting at the intersection between tube and bottom
0
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)
mf
γ Total resistance factor (γ = γ × γ )
R R m s
γ Specific resistance factor
s
Δσ Stress range
Δσ Bending stress range in the tube
b
Δσ Characteristic fatigue strength
c
Δσ Membrane stress range in the tube (axial)
m
Δσ Limit design stress range
Rd
Δσ Design stress range
Sd
Δp Design pressure range on piston side
Sd
δ Maximum displacement
max
κ Reduction factor for buckling
λ Slenderness
λ Friction parameters
i
μ Friction factors
i
ν Poisson’s ratio (ν = 0,3 for steel)
σ Axial stress in the tube
a
σ Lower extreme value of a stress range
b
σ Radial stress in the tube
r
σ Design stress, normal
Sd
σ Design weld stress, normal
w,Sd
σ Tangential stress in the tube (hoop stress)
t
σ Upper extreme value of a stress range
u
τ Design stress, shear
Sd
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 =
t
C +
D
o
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;
o
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)
p
and Formula (2) give design pressures p caused by forces acting on the cylinder from the crane
Sd
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
Sd
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
Sd
test pressure shall be multiplied by a partial safety factor γ equal to 1,05.
p
The design pressure p in the piston side chamber or in the rod side chamber shall be computed from
Sd
the design force F taking into account the force direction and the cylinder efficiency η due to friction.
Sd
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
Sd
p = ⋅Ψ (1)
Sd
2
π⋅D
where
F is the external design force;
Sd
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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
Sd
p = ⋅+Ψ p (2)
Sd Sde
22
π⋅−Dd
()
where
F is the external design force;
Sd
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):
Rd
ff= f ,γ (3)
()
Rd nk R
where
f is a general function as described in 6.2.2;
n
f is the characteristic values (or nominal value);
k
γ is the total resistance factor.
R
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
Rd
Formulae (4) and (5):
f
y
f = for normal stresses (4)
Rdσ
γ
Rm
f
y
f = for shear stresses (5)
Rdτ
γ ⋅ 3
Rm
with γγ= · γ
Rm msm
where
f is the minimum value of the yield stress of the material;
y
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ISO 23778:2022(E)
is the general resistance factor γ =11, (see ISO 8686-1);
γ
m
m
γ is the specific resistance factor for material in accordance with ISO 20332;
sm
γ = 0,95 is the basic value for material not loaded perpendicular to the rolling plane.
sm
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
sm
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
i1
Figure 6 — Pushing cylinder with supported bottom
Key
p pressure in piston side chamber
i1
Figure 7 — Pushing cylinder, flange mounted with unsupported bottom
Key
p
...