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Section 3a

Turbomachinery / Steam Turbines

A. General

1. Scope

The following Rules apply to main and auxiliarysteam turbines.

GL reserve the right to authorize deviations from therequirements in the case of low-power turbines.

2. Documents for approval

For every steam turbine installation, the documentslisted below are to be submitted to GL in triplicate forapproval:

assembly and sectional drawings of the turbines

detail drawings of rotors, casings, guide blading,blades, valves, bed frames and main condenser(for gearing, see Section 5)

details of operating characteristics and criticalspeeds

proof of a sufficient safety margin in the com-

ponents subject to the severest loads; for tem-peratures up to approximately 400 C, the rele-vant strength characteristic is the yield point atelevated temperatures; for higher temperatures itis the long-term creep strength for 100000 hoursat service temperature

details of the welding conditions applicable towelded components

on request, calculations relating to blade vibration

For small auxiliary turbines with a steam inlet tem-perature of up to 250 C it is generally sufficient tosubmit sectional drawings of the turbines.

Heat flow diagrams for each turbine installation and aset of operating instructions for at least each turbinetype are to be submitted.

B. Materials

1. Approved materials

1.1 Rotating components

Turbine rotors, discs and shafts are to be manufactured

from forged steel.The rotors of small turbines may also be cast in special-grade steel. Turbine blades, shrouds, binding and damp-ing wires are to be made of corrosion-resistant materials.

1.2 Stationary components

The casings of high-pressure turbines and the bodiesof manoeuvring, quick-closing and throttle valves areto be made of high-temperature steel or cast steel.Depending upon pressure and temperature, the casingsof intermediate and low-pressure turbines may also bemade of nodular or grey cast iron.

Diaphragms (guide vanes) are to be manufacturedfrom steel, cast steel, nodular or grey cast iron depend-

ing on the temperature and load. Welded constructionmay also be approved for steel or cast steel compo-nents.

Grey and nodular cast iron may be used up to a steamtemperature of 300 C.

2. Testing of materials

2.1 The following parts are subject to testing inaccordance with GL Rules II Materials and Weld-ing:

rotating parts such as rotors, discs, shafts, shrinkrings, blades, toothed couplings and other dy-namically loaded components as well as valvespindles and cones

stationary parts such as casings, guide blading,nozzles and nozzle chests, guide vanes, turbinecasing bolts, bed frames and bearing pedestals

condenser tubes and tube plates

In the case of small auxiliary turbines with a steaminlet temperature of up to 250 C, the extent of thetests may be limited to the disc and shaft materials.

C. Design and Construction Principles

1. Foundations

The foundations of geared turbine installations are tobe so designed and constructed that only minor rela-tive movements can occur between the turbine and thegearing which can be compensated by suitable cou-plings.

For the design of foundation also VI AdditionalRules and Guidelines, Part 4 Diesel Engines, Chap-ter 3 Guidelines for the Seating of PropulsionPlants and Auxiliary Machinery have to be consid-ered.

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2. Jointing of mating surfaces

The mating flanges of casings shall form a tight jointwithout the use of any interposed material.

3. Bearing lubricationThe lubrication of bearings are not to be impaired byadjacent 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 waythat no unacceptably high forces or moments can betransmitted to the turbine.

5. Drains

Turbines and the associated piping systems are to beequipped with adequate means of drainage.

6. Turning gear

Main propulsion turbines are to be equipped with turn-ing gear for both directions of rotation. The rotors ofauxiliary turbines are at least to be capable of beingturned by hand.

7. Measurement of rotor clearances

After assembly of each turbine in the manufacturer'sworks, the rotor position and the clearances are to be

determined. The clearances are to be specified in theoperating instructions.

8. Vibrations

The range of service speeds of turbine plant is not togive rise to unacceptable bending vibrations or to vi-

brations affecting the entire installation 1.

D. Astern Running, Emergency Operation

1. Astern power for main propulsion

1.1 The main propulsion machinery is to possesssufficient power for running astern. The astern poweris considered to be sufficient if, given free runningastern, it is able to attain astern revolutions equivalentto at least 70 % of the rated ahead revolutions for aperiod of at least 30 minutes.

1.2 For main propulsion machinery with reversegearing, controllable pitch propellers or an electricaltransmission system, astern running is not to cause anyoverloading of the propulsion machinery.

1 The assessment may be based on ISO 10816-3 "Mechanicalvibration Evaluation of machine vibration by measurementson non-rotating parts" or an equivalent standard.

2. Arrangements for emergency operation

In single screw ships fitted with cross compoundsteam turbines, the arrangements are to be such as toenable safe operation when the steam supply to any

one of the turbines is isolated. For this emergencyoperation purpose the steam may be led directly to thelower pressure turbine and either the high or mediumpressure part may exhaust directly to the condenser.Adequate arrangements and controls are to be pro-vided for these operating conditions so that the pres-sure and temperature of the steam will not exceedthose which the turbines and condenser are designedfor, thus enabling a long term safe operation underemergency conditions.

The necessary pipes and valves for these arrangementsare to be readily available and properly marked. A fitup test of all combinations of pipes and valves is to be

presented to GL prior to the first sea trials.

The permissible operating conditions (power/speeds)when operating without one of the turbines (all com-binations) are to be specified and accessibly docu-mented on board.

The operation of the turbines under emergency condi-tions is to be assessed by calculations for the potentialinfluence on shaft alignment and gear teeth loadingconditions. Corresponding documentation shall besubmitted to GL for appraisal.

E. Manoeuvring and Safety Equipment

1. Manoeuvring and control equipment

1.1 The simultaneous admission of steam to theahead and astern turbines is to be prevented by inter-locks. Brief overlapping of the ahead and astern valvesduring manoeuvring can be allowed.

1.2 Fluids for operating manoeuvring equipment,quick-closing and control systems are to be suitable

for all service temperatures and of low flammability.

1.3 Turbines for main propulsion machineryequipped with controllable pitch propellers, disengag-ing couplings or an electrical transmission system areto be fitted with a speed governor which, in the eventof a sudden loss of load, prevents the revolutions fromincreasing to the trip speed.

1.4 The speed increase of turbines driving elec-tric generators - except those for electrical propellerdrive - resulting from a change from full load to no-load may not exceed 5 % on the resumption of steadyrunning conditions. The transient speed increase re-sulting from a sudden change from full load to no-loadconditions may not exceed 10 % and is to be separatedby a sufficient margin from the trip speed.

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2. Safety devices

2.1 Main propulsion turbines are to be equippedwith 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 pres-sure

d) an unacceptable increase in the condenser waterlevel and

e) an unacceptable drop in the lubricating oil pres-sure

2.2 In cases a) and b) of 2.1, the quick-closingdevices shall be actuated by the turbine shafts.

2.3 It also is to be possible to trip the quick-closing device manually at the turbine and from thecontrol platform.

2.4 Re-setting of the quick-closing device may beeffected only at the turbine or from the control plat-form with the control valve in the closed position.

2.5 It is recommended that an alarm systemshould be fitted which responds to excessive vibration

velocities 1.

2.6 An interlock is to be provided to ensure thatthe main turbine cannot be started up when the turninggear is engaged.

2.7 Steam bleeder and pass-in lines are to be fit-ted with automatic devices which prevent steam fromflowing into the turbine when the main steam admis-sion valve is closed.

2.8 Turbines driving auxiliary machines at leastare to be equipped with quick-closing devices for con-tingencies a) and d) of 2.1. An excessive rise in theexhaust steam pressure is to actuate the quick-closingdevice.

2.9 It shall be possible to start up any turbineonly when the quick-closing device is ready for opera-tion.

3. Other requirements

Depending on the degree of automation involved, theextent and design of the equipment is also subject tothe requirements in Chapter 4 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 plat-form.

2. Scope and design of equipment

Depending on the degree of automation involved, thescope and design of the equipment is also subject tothe Rules in Chapter 4 Automation.

3. Control and indicating instruments

When the turning gear is engaged, this fact is to beindicated visually at the control platform.

Turbine and pipeline drainage valves are either to op-erate automatically or are to be combined into groupswhich can be operated from the control platform.

4. Equipment for auxiliary turbines

Turbines driving auxiliary machines are to be pro-vided with the necessary equipment on the basis of 2.and 3.

G. Condensers

1. Design

The condenser is to be so designed that the inlet steamspeed does not result in prohibitive stressing of thecondenser tubes. Excessive sagging of the tubes andvibration are to be avoided, e.g. by the incorporationof tube supporting plates.

Thewaterchambersandsteamspacearetobeprovidedwith openings for inspection and cleaning. Anti-corrosionprotectionistobeprovidedonthewaterside.

In the case of single-plane turbine installations, suit-able measures are to be taken to prevent condensate

from flowing back into the low pressure turbine.

2. Cooling water supply

The supply of cooling water to the condenser is sub-ject to the requirements contained in Section 11, I.

H. Tests

1. Testing of turbine rotors

1.1 Thermal stability testRotors forged in one piece and welded rotors are to betested for axial stability by submitting them to a ther-mal stability test.

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1.2 Balancing

Finished rotors, complete with blades and associatedrotating parts and ready for assembly, are to be dy-

namically balanced in the presence of the Surveyor.2

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.GL may accept mathematical proof of the stresses inthe rotating parts at overspeed as a substitute for theoverspeed test itself, provided that the design is suchthat reliable calculations are possible and the rotor hasbeen non-destructively tested to ascertain its freedomfrom defects.

2. Pressure and tightness tests

2.1 All finished casing components are to be sub-jected to hydrostatic testing in the presence of the Sur-veyor.

The test pressure ppis calculated as follows:

where pe,zul80 bar: pp= 1,5 pe,zul

where pe,zul> 80 bar: pp= pe,zul+ 40 bar

pe,zul= maximum allowable working pressure [bar]

For the bodies of quick-closing, manoeuvring andcontrol valves, the test pressure is 1,5 times the maxi-mum allowable working pressure of the boiler (ap-

proval pressure). The sealing efficiency of thesevalves when closed is to be tested at 1,1 pe,zul.

2.2 Casing parts on the exhaust side of low pres-sure turbines subjected during operation to the con-denser pressure are to be tested at pp= 1,0 bar.

2 The assessment may be based on ISO 1940-1 standard "Me-chanical vibration Balance quality requirements of rigid ro-tors" or an equivalent standard.

2.3 Condensers are to be subjected to separatehydrostatic testing on both the steam and the waterside. The test pressure ppshall be:

pp = 1,0 bar on the steam side

pp = 1,5 pe,zul on the water side

I. Trials

1. Factory trials

Where steam turbines are subjected to a trial run at thefactory, the satisfactory functioning of the manoeu-vring, safety and control equipment is to be verifiedduring the trial run, and such verification shall in any

case take place not later than the commissioning of theplant aboard ship.

2. Shipboard trials

2.1 Main turbines are to be subjected to a docktrial and thereafter, during a trial voyage, to the fol-lowing tests:

operation at rated rpm for at least 6 hours

reversing manoeuvres

during the dock or sea trials, astern revolutions

equal to at least 70 % of the rated ahead rpm forabout 20 minutes

During astern and subsequent forward operation, thesteam pressures and temperatures and the relative ex-pansion are not to reach magnitudes liable to endangerthe operational safety of the plant.

2.2 Turbines driving electric generators or auxil-iary machines are to be run for at least 4 hours at theirrated power and for 30 minutes at 110 % rated power.

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