Section 3 Construction and design

3.1 General

3.1.1 Rudder actuators other than those covered by Pt 5, Ch 19, 8.3 For oil storage units of 10 000 tons gross and upwards but of less than 100 000 tons deadweight and the ‘Guidelines’ are to be designed in accordance with the relevant requirements of Pt 5, Ch 11 Other Pressure Vessels for Class I pressure vessels (notwithstanding any exemptions for hydraulic cylinders).

3.1.2 Accumulators, if fitted, are to comply with the relevant requirements of Pt 5, Ch 11 Other Pressure Vessels.

3.1.3 The welding details and welding procedures are to be approved. All welded joints within the pressure boundary of a rudder actuator or connecting parts transmitting mechanical loads are to be of full penetration type or of equivalent strength.

3.1.4 The construction is to be such as to minimise local concentrations of stress.

3.1.5 The design pressure for calculations to determine the scantlings of piping and other steering gear components subjected to internal hydraulic pressure shall be at least 1,25 times the maximum working pressure, which is to be expected under the operational conditions specified in Pt 5, Ch 19, 2.1 General 2.1.2, taking into account any pressure which may exist in the low pressure side of the system. Fatigue criteria may be applied for the design of piping and components, taking into account pulsating pressures due to dynamic loads, see Pt 5, Ch 19, 9 ‘Guidelines’ for the acceptance of non-duplicated rudder actuators for oil storage units of 10 000 tons gross and upwards but of less than 100 000 tons deadweight.

3.1.6 For the rudder actuator, the permissible primary general membrane stress is not to exceed the lower of the following values:

where

specified minimum tensile strength of material at ambient temperature

specified minimum yield stress or 0,2 per cent proof stress of the material at ambient temperature A and B are given by the following Table:

	Wrought steel	Cast steel	Nodular cast iron
A	3,5	4	5
B	1,7	2	3

3.2 Components

3.2.1 Special consideration is to be given to the suitability of any essential component which is not duplicated. Any such essential component shall, where appropriate, utilise anti-friction bearings such as ball bearings, roller bearings or sleeve bearings which shall be permanently lubricated or provided with lubrication fittings.

3.2.2 All steering gear components transmitting mechanical forces to the rudder stock, which are not protected against overload by structural rudder stops or mechanical buffers, are to have a strength of at least the equivalent to that of the rudder stock in way of the tiller.

3.2.3 Actuator oil seals between non-moving parts, forming part of the external pressure boundary, are to be of the metal type or of an equivalent type.

3.2.4 Actuator oil seals between moving parts, forming part of the external pressure boundary, are to be duplicated, so that the failure of one seal does not render the actuator inoperative. Alternative arrangements providing equivalent protection against leakage may be accepted.

3.2.5 Piping, joints, valves, flanges and other fittings are to comply within the requirements of Pt 5, Ch 12 Piping Design Requirements for Class I piping systems components. The design pressure is to be in accordance with Pt 5, Ch 19, 3.1 General 3.1.5

3.2.6 Hydraulic power-operated steering gears are to be provided with the following:

Arrangements to maintain the cleanliness of the hydraulic fluid, taking into consideration the type and design of the hydraulic system;
A fixed storage tank having sufficient capacity to recharge at least one power actuating system including the reservoir, where the main steering gear is required to be power-operated. The storage tank is to be permanently connected by piping, in such a manner that the hydraulic systems can be readily recharged from a position within the steering gear compartment and provided with a contents gauge.

3.3 Valve and relief valve arrangements

3.3.1 For vessels with non-duplicated actuators, isolating valves are to be fitted at the connection of pipes to the actuator, and are to be directly fitted on the actuator.

3.3.2 Arrangements for bleeding air from the hydraulic system are to be provided, where necessary.

3.3.3 Relief valves are to be fitted to any part of the hydraulic system which can be isolated and where pressure can be generated from the power source or from external forces. The settings of the relief valves is not to exceed the design pressure. The valves are to be of adequate size and so arranged as to avoid an undue rise in pressure above the design pressure.

3.3.4 Relief valves for protecting any part of the hydraulic system which can be isolated, as required by 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.
the minimum discharge capacity of the relief valve(s) is not to be less than 110 per cent of the total capacity of the pumps which can be delivered through them. Under such conditions, the rise in pressure is not to exceed 10 per cent of the setting pressure. In this regard, due consideration is to be given to extreme foreseen ambient conditions, in respect of oil viscosity.

3.4 Flexible hoses

3.4.1 Hose assemblies approved by LR may be installed between two points where flexibility is required but are not to be subjected to torsional deflection (twisting) under normal operating conditions. In general, the hose should be limited to the length necessary to provide for flexibility and for proper operation of machinery, see also Pt 5, Ch 12 Piping Design Requirements

3.4.2 Hoses should be high pressure hydraulic hoses, according to recognised standards and should be suitable for the fluids, pressures, temperatures and ambient conditions in question.

3.4.3 Burst pressure of hoses is to be not less than four times the design pressure.