1. Scope
The following Rules apply to main and auxiliary steam turbines.
The Society reserves the right to authorize deviations from the Rules in the case of low-power turbines.
2. Documents for approval
For every steam turbine installation, the documents listed below under a) to f) are to be submitted to the Society in triplicate1) for approval:
a) Assembly and sectional drawings of the turbines,
b) Detail drawings of rotors, casings,
diaphragms, blades, valves, bed frames and main condenser (for gearing, see Section 5), c) Details of operating characteristics and
critical speeds,
d) Proof of a sufficient safety margin in the components subject to the severest loads. For temperatures up to approximately 400 oC, the relevant strength characteristic is the yield point at elevated temperatures; for higher temperatures it is the long-term creep strength or the 1 % time yield limit for 100.000 hours at service temperature, e) Details of the welding conditions applicable
to welded components and
f) On request, calculations relating to blade vibration.
For small auxiliary turbines with a steam inlet temperature of up to 250 C it is generally sufficient to submit sectional drawings of the turbines. Heat flow diagrams for each turbine installation and a set of operating instructions for at least each turbine type are to be submitted.
B. Materials
1. Approved materials
1.1 Rotating components
Turbine rotors, discs and shafts are to be manufac- tured from forged steel.
The rotors of small turbines may also be cast in spe- cial-grade steel. Turbine blades, shrouds, binding and damping wires are to be made of corrosion-resistant materials.
1.2 Stationary components
The casings of high-pressure turbines and the bodies of manoeuvering, quick-closing and throttle valves are to be made of high-temperature steel or cast steel. Depending upon pressure and temperature, the casings of intermediate and low-pressure turbines may also be made of nodular or grey cast iron.
Diaphragms are to be manufactured from steel, cast steel, nodular or grey cast iron depending on the temperature and load. Welded construction may also bc approved for steel or cast steel components. Grey and nodular cast iron may be used up to a steam temperature of 300 oC.
2. Testing of materials
2.1 The following parts are subject to testing in accordance with the Society's Rules for Materials: a) Rotating parts such as rotors, discs, shafts,
shrink rings, blades, toothed couplings and other dynamically loaded components as well as valve spindles and cones.
b) Stationary parts such as casings, diaphragms, nozzles and nozzle chests, guide vanes, turbine casing bolts, bed frames and bearing pedestals.
c) Condenser tubes and tube plates.
In the case of small auxiliary turbines with a steam inlet temperature of up to 250 C, the extent of the tests may be limited to the disc and shaft materials.
C. Design and Construction Principles
1. Foundations
The foundations of geared turbine installations are to be so designed and constructed that only minor rela- tive movements can occur between the turbine and the gearing which can be compensated by suitable couplings.
2. Jointing of mating surfaces
The mating flanges of casings must form a tight joint without the use of any interposed material.
3. Bearing lubrication
The lubrication of bearings must not be impaired by adjacent hot parts or by steam.
For the lubricating oil system, see Section 11, H.
4. Connections
Pipes are to be connected to the turbine in such a way that no unacceptably high forces or moments can be transmitted to the turbine.
5. Drains
Turbines and the associated piping systems are to be equipped with adequate means of drainage.
6. Turning gear
Main propulsion turbines are to be equipped with turning gear for both directions of rotation. The rotors of auxiliary turbines must at least be capable of being turned by hand.
7. Measurement of rotor clearances
After assembly of each turbine in the manufacturer's works, the rotor position and the clearances are to be determined. The clearances are to be specified in the operating instructions.
8. Vibrations
The range of service speeds of turbine plant must not give rise to unacceptable bending vibrations or to vi- brations affecting the entire installation1) .
D. Astern Running, Emergency Operation
1. Astern power for main propulsion 1.1 The main propulsion machinery must possess
sufficient power for running astern. The astern power is considered to be sufficient if, given free running astern, it is able to attain astern revolutions equivalent to at least 70 % of the rated ahead revolutions for a period of at least 30 minutes.
1.2 For main propulsion machinery with reverse gearing, controllable pitch propellers or an electrical transmission system, astern running must not cause any overloading of the propulsion machinery.
2. Arrangements for emergency operation
In single screw ships fitted with multi-cylinder steam turbines, the arrangement is to be such as to ensure safe operation when the steam led to any one of the cylinders is cut off. For this purpose, means are to be provided either for supplying steam directly to the low-pressure turbine or for conveying the exhaust steam from the high or intermediate pressure turbine directly to the condenser.
With a view to such emergency operation, suitable equipment is to be provided to prevent the permissible steam pressures and temperatures for the turbines and condenser from being exceeded.
E. Manoeuvering and Safety Equipment
1. Manoeuvering and control equipment 1.1 The simultaneous admission of steam to the ahead and astern turbines is to be prevented by interlocks. Brief overlapping of the ahead and astern valves during manoeuvering can be allowed.
1.2 Fluids for operating hydraulic manoeuvering equipment, quick-closing and control systems must be suitable for all service temperatures and of low flammability.
1.3 Turbines for main propulsion machinery equipped with controllable pitch propellers, disen- gaging couplings or an electrical transmission system are to be filled with a speed governor which, in the event of a sudden loss of load, prevents the revolu- tions from increasing to the trip speed.
1.4 The speed increase of turbines driving electric generators - except those for electrical pro- peller drive - resulting from a change from full load to no-load may not exceed 5 % on the resumption of steady running conditions. The transient speed increase resulting from a sudden change from full load to no-load conditions may not exceed 10 % and must be separated by a sufficient margin from the trip speed.
2. Safety devices
2.1 Main propulsion turbines must be equipped 1
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with quick-closing devices which automatically shut off the steam supply in case of:
a) Overspeed. Excess speeds of more than 15 % above the rated value are to be prevented, b) unacceptable axial displacement of the rotor, c) an unacceptable increase in the condenser
pressure,
d) an unacceptable increase in the condenser water level and
e) an unacceptable drop in the lubricating oil pressure.
2.2 In cases a) and b), the quick-closing devices must be actuated by the turbine shafts.
2.3 It must also be possible to trip the quick- closing device manually at the turbine and from the control platform.
2.4 Re-setting of the quick-closing device may be effected only at the turbine or from the control platform with the control valve in the closed position. 2.5 It is recommended that an alarm system should be fitted which responds to excessive vibration velocities1) .
2.6 An interlock is to be provided to ensure that the main turbine cannot be started up when the turning gear is engaged.
2.7 Steam bleeder and pass-in lines are to be fitted with automatic devices which prevent steam from flowing into the turbine when the main steam admission valve is closed.
2.8 Turbines driving auxiliary machines must at least be equipped with quick-closing devices for contingencies 2.1 a and 2.1 d. An excessive rise in the exhaust steam pressure must actuate the quickclosing device.
2.9 It shall be possible to start up any turbine only when the quick-closing device is ready for operation.
3. Other Rules
Depending on the degree of automation involved, the extent and design of the equipment is also subject to Volume VII, Rules for Automation.
F. Control and Monitoring Equipment
1. Arrangement
The control and monitoring equipment for each main propulsion unit is to be located on the control
platform.
2. Scope and design of equipment
Depending on the degree of automation involved, scope and design of the equipment is also subject to Volume VII, Rules for Automation.
3. Control and indicating instruments
When the turning gear is engaged, this fact must be indicated visually at the control platform.
Turbine and pipeline drainage valves are either to operate automatically or are to be combined into groups which can be operated from the control platform.
4. Equipment for auxiliary turbines
Turbines driving auxiliary machines are to be provided with the necessary equipment on the basis of paragraphs 2 and 3.
G. Condensers
1. Design
The condenser is to be so designed that the inlet steam speed not to prohibitive stressing of the condenser tubes result. Excessive sagging of the tubes and vibration are to be avoided, e.g. by the incorporation of tube supporting plates.
The water chambers and steam space must be provided with openings for inspection and cleaning. Anti-corrosion protection is to be provided on the water side.
ln the case of single-plane turbine installations, suitable measures must be taken to prevent condensate from flowing back into the LP turbine.
2. Cooling water supply
The supply of cooling water to the condenser is subject to the Rules contained in Section 11, J.
H. Tests
1. Testing of turbine rotors
1.1 Thermal stability test
Rotors forged in one piece and welded rotors are to be tested for axial stability by submitting them to a 1
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thermal stability test. 1.2 Balancing1)
Finished rotors, complete with blades and associated rotating parts and ready for assembly, are to be dynamically balanced in the presence of the Surveyor.
1.3 Cold overspeed test
Turbine rotors are to be tested at a speed at least 15 % above the rated speed for not less than three minutes. The Society may accept mathematical proof of the stresses in the rotating parts at overspeed as a substitute for the overspeed test itself provided that the design is such that reliable calculations are possible and the rotor has been non-destructively tested to ascertain its freedom from defects.
2. Pressure and tightness tests
2.1 All finished casing components are to be subjected to hydrostatic testing in the presence of the Surveyor.
The test pressure pp is calculated as follows: pP = 1,5 pe,perm
where pe,perm 80 bar pP = pe,perm + 40 bar
where pe,perm > 80 bar
pe,perm [bar]= maximum allowable working pressure
For the bodies of quick-closing, manoeuvering and control valves, the test pressure is 1,5 times the maximum allowable working pressure of the boiler (approval pressure). The sealing efficiency of these valves when closed is lo be tested at 1,1 pe,perm
2.2 Casing parts on the exhaust side of LP turbines subjected during operation to the condenser pressure are to be tested at pp = 1,0 bar.
2.3 Condensers are to be subjected to separate hydrostatic testing on both the steam and the water side. The test pressure shall be:
pp = 1,0 bar on the steam side
pp = 1,5 pe,perm on the water side
I. Trials
1. Factory Trials
Where steam turbines are subjected to a trial run at the factory, the satisfactory functioning of the manoeuvering, safety and control equipment is to be verified during the trial run, and such verification shall in any case take place not later than the commissioning of the plant aboard ship.
2. Shipboard trials
2.1 Main turbines are to be subjected to a dock trial and thereafter, during a trial voyage, to the following tests:
a) Operation at rated rpm for at least 6 hours,
b) Reversing manoeuvres, and
c) During the dock or sea trials, astern revolutions equal to at least 70 % of the rated ahead rpm for about 20 minutes. During astern and subsequent forward operation, the steam pressures and temperatures and the relative expansion must not assume magnitudes liable to endanger the operational safety of the plant.
2.2 Turbines driving electric generators or auxiliary machines are to be run for at least 4 hours at their rated power and for 30 minutes at 110 % rated power.
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