Section
9 'Guidelines' for the acceptance of non-duplicated rudder actuators
for tankers, chemical tankers and gas carriers of 10 000 tons gross
and upwards but of less than 100 000 tons deadweight
9.1 Materials
9.1.1 Parts
subject to internal hydraulic pressure or transmitting mechanical
forces to the rudder-stock are to be made of duly tested ductile materials
complying with recognised Standards. Materials for pressure retaining
components are to be in accordance with recognised pressure vessel
Standards. These materials are not to have an elongation less than
12 per cent nor a tensile strength in excess of 650 N/mm2.
9.2 Design
9.2.2
Analysis. In order to analyse the design the following are required:
-
The manufacturers
of rudder actuators should submit detailed calculations showing the
suitability of the design for the intended service.
-
A detailed stress
analysis of pressure retaining parts of the actuator should be carried
out to determine the stresses at the design pressure.
-
Where considered
necessary because of the design complexity or manufacturing procedures,
a fatigue analysis and fracture mechanics analysis may be required.
In connection with these analyses, all foreseen dynamic loads should
be taken into account. Experimental stress analysis may be required
in addition to, or in lieu of, theoretical calculations depending
upon the complexity of the design.
9.2.4
Allowable
stresses. For the purpose of determining the general scantlings
of parts of rudder actuators subject to internal hydraulic pressure
the allowable stresses should not exceed:
σm ≤ f
σ1 ≤ 1,5f
σb ≤1,5f
σ1 + σb ≤ 1,5f
σm + σb≤ 1,5f
where
|
= |
|
σb
|
= |
equivalent
primary bending stress |
σm
|
= |
equivalent
primary general membrane stress |
σy
|
= |
specified
minimum yield stress or 0,2 per cent proof stress of material at ambient
temperature |
σB
|
= |
specified
minimum tensile strength of material at ambient temperature |
σ1
|
= |
equivalent
primary local membrane stress |
A and B are as follows:
|
Wrought steel
|
Cast steel
|
Nodular cast iron
|
A
|
4
|
4,6
|
5,8
|
B
|
2
|
2,3
|
3,5
|
9.2.5
Burst
test. Pressure retaining parts not requiring fatigue analysis
and fracture mechanics analysis may be accepted on the basis of a
certified burst test and the detailed stress analysis required by Pt 5, Ch 19, 9.2 Design 9.2.2 need not be provided.
The minimum bursting pressure should be calculated as follows:
9.3 Construction details
9.3.1
General. The construction should be such as to minimise local concentrations
of stress.
9.3.2
Welds.
-
The welding details
and welding procedures should be approved.
-
All welded joints
within the pressure boundary of a rudder actuator or connection parts
transmitting mechanical loads should be full penetration type or of
equivalent strength.
9.3.4
Isolating
valves are to be fitted at the connection of pipes to the actuator,
and should be directly mounted on the actuator.
9.3.5
Relief
valves for protecting the rudder actuator against over-pressure
as required in Pt 5, Ch 19, 3.3 Valve and relief valve arrangements 3.3.3 are
to comply with the following:
-
The setting pressure is not to be less than 1,25 times the maximum
working pressure expected under operating conditions required by Pt 5, Ch 19, 2.2 Performance requirements for rudder-type steering systems 2.2.1.(a).
-
The minimum discharge
capacity of the relief valve(s) is to be not less than 110 per cent
of the total capacity of all pumps which provide power for the actuator.
Under such conditions the rise in pressure should not exceed 10 per
cent of the setting pressure. In this regard due consideration should
be given to extreme foreseen ambient conditions in respect of oil
viscosity.
9.4 Non-destructive testing
9.4.1 The
rudder actuator should be subjected to suitable and complete non-destructive
testing to detect both surface flaws and volumetric flaws. The procedure
and acceptance criteria for non-destructive testing should be in accordance
with requirements of recognised Standards. If found necessary, fracture
mechanics analysis may be used for determining maximum allowable flaw
size.
9.5 Testing
9.5.1 Tests,
including hydrostatic tests, of all pressure parts at 1,5 times the
design pressure should be carried out subject to any limitations imposed
by valves and other components. Where additional testing of systems
or subsystems following final assembly is required, the test pressure
may be subject to any limitations imposed by valves and other components.
9.5.2 When
installed on board the ship, the rudder actuator should be subjected
to a hydrostatic test at the pressure defined in Pt 5, Ch 19, 9.5 Testing 9.5.1 and a running test.
9.6 Additional requirements for steering gear fitted to ships with
Ice Class notations
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