(I-1-2) Section 3a Turbomachinery Steam Turbines

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					I - Part 1    Section 3a      C    Turbomachinery / Steam Turbines                                           Chapter 2
GL 2009                                                                                                      Page 3a–1

                                                     Section 3a

                                  Turbomachinery / Steam Turbines

A.       General                                             1.2        Stationary components

1.       Scope                                               The casings of high-pressure turbines and the bodies
                                                             of manoeuvring, quick-closing and throttle valves are
The following Rules apply to main and auxiliary              to be made of high-temperature steel or cast steel.
steam turbines.                                              Depending upon pressure and temperature, the casings
                                                             of intermediate and low-pressure turbines may also be
GL reserve the right to authorize deviations from the
                                                             made of nodular or grey cast iron.
requirements in the case of low-power turbines.
                                                             Diaphragms (guide vanes) are to be manufactured
2.       Documents for approval                              from steel, cast steel, nodular or grey cast iron depend-
                                                             ing on the temperature and load. Welded construction
For every steam turbine installation, the documents          may also be approved for steel or cast steel compo-
listed below are to be submitted to GL in triplicate for     nents.
                                                             Grey and nodular cast iron may be used up to a steam
–     assembly and sectional drawings of the turbines
                                                             temperature of 300 °C.
–     detail drawings of rotors, casings, guide blading,
      blades, valves, bed frames and main condenser          2.         Testing of materials
      (for gearing, see Section 5)
–     details of operating characteristics and critical      2.1     The following parts are subject to testing in
      speeds                                                 accordance with GL Rules II – Materials and Weld-
–     proof of a sufficient safety margin in the com-
      ponents subject to the severest loads; for tem-        –       rotating parts such as rotors, discs, shafts, shrink
      peratures up to approximately 400 °C, the rele-                rings, blades, toothed couplings and other dy-
      vant strength characteristic is the yield point at             namically loaded components as well as valve
      elevated temperatures; for higher temperatures it              spindles and cones
      is the long-term creep strength for 100000 hours
      at service temperature                                 –       stationary parts such as casings, guide blading,
                                                                     nozzles and nozzle chests, guide vanes, turbine
–     details of the welding conditions applicable to                casing bolts, bed frames and bearing pedestals
      welded components
                                                             –       condenser tubes and tube plates
–     on request, calculations relating to blade vibration
                                                             In the case of small auxiliary turbines with a steam
For small auxiliary turbines with a steam inlet tem-
                                                             inlet temperature of up to 250 °C, the extent of the
perature of up to 250 °C it is generally sufficient to
                                                             tests may be limited to the disc and shaft materials.
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.                                    C.         Design and Construction Principles

                                                             1.         Foundations
B.       Materials
                                                             The foundations of geared turbine installations are to
                                                             be so designed and constructed that only minor rela-
1.       Approved materials                                  tive movements can occur between the turbine and the
                                                             gearing which can be compensated by suitable cou-
1.1      Rotating components                                 plings.
Turbine rotors, discs and shafts are to be manufactured
                                                             For the design of foundation also VI – Additional
from forged steel.
                                                             Rules and Guidelines, Part 4 – Diesel Engines, Chap-
The rotors of small turbines may also be cast in special-    ter 3 – Guidelines for the Seating of Propulsion
grade steel. Turbine blades, shrouds, binding and damp-      Plants and Auxiliary Machinery have to be consid-
ing wires are to be made of corrosion-resistant materials.   ered.
Chapter 2        Section 3a      E      Turbomachinery / Steam Turbines                                          I - Part 1
Page 3a–2                                                                                                        GL 2009

2.        Jointing of mating surfaces                              2.       Arrangements for emergency operation
The mating flanges of casings shall form a tight joint             In single screw ships fitted with cross compound
without the use of any interposed material.                        steam turbines, the arrangements are to be such as to
                                                                   enable safe operation when the steam supply to any
3.        Bearing lubrication                                      one of the turbines is isolated. For this emergency
                                                                   operation purpose the steam may be led directly to the
The lubrication of bearings are not to be impaired by              lower pressure turbine and either the high or medium
adjacent hot parts or by steam.                                    pressure part may exhaust directly to the condenser.
For the lubricating oil system, see Section 11, H.                 Adequate arrangements and controls are to be pro-
                                                                   vided for these operating conditions so that the pres-
4.        Connections                                              sure and temperature of the steam will not exceed
                                                                   those which the turbines and condenser are designed
Pipes are to be connected to the turbine in such a way             for, thus enabling a long term safe operation under
that no unacceptably high forces or moments can be                 emergency conditions.
transmitted to the turbine.
                                                                   The necessary pipes and valves for these arrangements
                                                                   are to be readily available and properly marked. A fit
5.        Drains
                                                                   up test of all combinations of pipes and valves is to be
Turbines and the associated piping systems are to be               presented to GL prior to the first sea trials.
equipped with adequate means of drainage.
                                                                   The permissible operating conditions (power/speeds)
                                                                   when operating without one of the turbines (all com-
6.        Turning gear
                                                                   binations) are to be specified and accessibly docu-
Main propulsion turbines are to be equipped with turn-             mented on board.
ing gear for both directions of rotation. The rotors of
auxiliary turbines are at least to be capable of being             The operation of the turbines under emergency condi-
turned by hand.                                                    tions is to be assessed by calculations for the potential
                                                                   influence on shaft alignment and gear teeth loading
                                                                   conditions. Corresponding documentation shall be
7.        Measurement of rotor clearances                          submitted to GL for appraisal.
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.                                            E.       Manoeuvring and Safety Equipment

8.        Vibrations
                                                                   1.       Manoeuvring and control equipment
The range of service speeds of turbine plant is not to
give rise to unacceptable bending vibrations or to vi-             1.1      The simultaneous admission of steam to the
brations affecting the entire installation 1.                      ahead and astern turbines is to be prevented by inter-
                                                                   locks. Brief overlapping of the ahead and astern valves
                                                                   during manoeuvring can be allowed.
D.        Astern Running, Emergency Operation
                                                                   1.2       Fluids for operating manoeuvring equipment,
                                                                   quick-closing and control systems are to be suitable
1.        Astern power for main propulsion                         for all service temperatures and of low flammability.
1.1       The main propulsion machinery is to possess
sufficient power for running astern. The astern power              1.3       Turbines for main propulsion machinery
is considered to be sufficient if, given free running              equipped with controllable pitch propellers, disengag-
astern, it is able to attain astern revolutions equivalent         ing couplings or an electrical transmission system are
to at least 70 % of the rated ahead revolutions for a              to be fitted with a speed governor which, in the event
period of at least 30 minutes.                                     of a sudden loss of load, prevents the revolutions from
                                                                   increasing to the trip speed.
1.2      For main propulsion machinery with reverse
gearing, controllable pitch propellers or an electrical            1.4       The speed increase of turbines driving elec-
transmission system, astern running is not to cause any            tric generators - except those for electrical propeller
overloading of the propulsion machinery.                           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 re-
1    The assessment may be based on ISO 10816-3 "Mechanical
                                                                   sulting from a sudden change from full load to no-load
     vibration – Evaluation of machine vibration by measurements   conditions may not exceed 10 % and is to be separated
     on non-rotating parts" or an equivalent standard.             by a sufficient margin from the trip speed.
I - Part 1    Section 3a     H   Turbomachinery / Steam Turbines                                       Chapter 2
GL 2009                                                                                                Page 3a–3

2.       Safety devices                                   F.       Control and Monitoring Equipment

2.1       Main propulsion turbines are to be equipped     1.       Arrangement
with quick-closing devices which automatically shut-
                                                          The control and monitoring equipment for each main
off the steam supply in case of:
                                                          propulsion unit is to be located on the control plat-
a)    overspeed. Excess speeds of more than 15 %          form.
      above the rated value are to be prevented
                                                          2.       Scope and design of equipment
b)    unacceptable axial displacement of the rotor
                                                          Depending on the degree of automation involved, the
c)    an unacceptable increase in the condenser pres-     scope and design of the equipment is also subject to
      sure                                                the Rules in Chapter 4 – Automation.

d)    an unacceptable increase in the condenser water     3.       Control and indicating instruments
      level and
                                                          When the turning gear is engaged, this fact is to be
e)    an unacceptable drop in the lubricating oil pres-   indicated visually at the control platform.
      sure                                                Turbine and pipeline drainage valves are either to op-
                                                          erate automatically or are to be combined into groups
2.2      In cases a) and b) of 2.1, the quick-closing     which can be operated from the control platform.
devices shall be actuated by the turbine shafts.
                                                          4.       Equipment for auxiliary turbines
2.3      It also is to be possible to trip the quick-     Turbines driving auxiliary machines are to be pro-
closing device manually at the turbine and from the       vided with the necessary equipment on the basis of 2.
control platform.                                         and 3.

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

2.5      It is recommended that an alarm system           1.       Design
should be fitted which responds to excessive vibration    The condenser is to be so designed that the inlet steam
velocities 1.                                             speed does not result in prohibitive stressing of the
                                                          condenser tubes. Excessive sagging of the tubes and
2.6      An interlock is to be provided to ensure that    vibration are to be avoided, e.g. by the incorporation
the main turbine cannot be started up when the turning    of tube supporting plates.
gear is engaged.
                                                          The water chambers and steam space are to be provided
                                                          with openings for inspection and cleaning. Anti-
2.7      Steam bleeder and pass-in lines are to be fit-   corrosion protection is to be provided on the water side.
ted with automatic devices which prevent steam from
flowing into the turbine when the main steam admis-       In the case of single-plane turbine installations, suit-
sion valve is closed.                                     able measures are to be taken to prevent condensate
                                                          from flowing back into the low pressure turbine.

2.8      Turbines driving auxiliary machines at least
                                                          2.       Cooling water supply
are to be equipped with quick-closing devices for con-
tingencies a) and d) of 2.1. An excessive rise in the     The supply of cooling water to the condenser is sub-
exhaust steam pressure is to actuate the quick-closing    ject to the requirements contained in Section 11, I.

2.9     It shall be possible to start up any turbine
only when the quick-closing device is ready for opera-    H.       Tests
                                                          1.       Testing of turbine rotors
3.       Other requirements                               1.1      Thermal stability test
Depending on the degree of automation involved, the       Rotors forged in one piece and welded rotors are to be
extent and design of the equipment is also subject to     tested for axial stability by submitting them to a ther-
the requirements in Chapter 4 – Automation.               mal stability test.
Chapter 2          Section 3a       I      Turbomachinery / Steam Turbines                                           I - Part 1
Page 3a–4                                                                                                            GL 2009

1.2        Balancing                                                   2.3      Condensers are to be subjected to separate
                                                                       hydrostatic testing on both the steam and the water
Finished rotors, complete with blades and associated
                                                                       side. The test pressure pp shall be:
rotating parts and ready for assembly, are to be dy-
namically balanced in the presence of the Surveyor. 2                  pp    = 1,0 bar       on the steam side

1.3        Cold overspeed test                                         pp    = 1,5 pe,zul    on the water side
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 in
the rotating parts at overspeed as a substitute for the                I.       Trials
overspeed test itself, provided that the design is such
that reliable calculations are possible and the rotor has              1.       Factory trials
been non-destructively tested to ascertain its freedom
from defects.                                                          Where steam turbines are subjected to a trial run at the
                                                                       factory, the satisfactory functioning of the manoeu-
                                                                       vring, safety and control equipment is to be verified
2.         Pressure and tightness tests
                                                                       during the trial run, and such verification shall in any
2.1      All finished casing components are to be sub-                 case take place not later than the commissioning of the
jected to hydrostatic testing in the presence of the Sur-              plant aboard ship.
The test pressure pp is calculated as follows:                         2.       Shipboard trials

where pe,zul ≤ 80 bar:           pp = 1,5 pe,zul                       2.1      Main turbines are to be subjected to a dock
                                                                       trial and thereafter, during a trial voyage, to the fol-
where pe,zul > 80 bar:           pp = pe,zul + 40 bar                  lowing tests:
pe,zul = maximum allowable working pressure [bar]                      –     operation at rated rpm for at least 6 hours
For the bodies of quick-closing, manoeuvring and                       –     reversing manoeuvres
control valves, the test pressure is 1,5 times the maxi-
mum allowable working pressure of the boiler (ap-                      –     during the dock or sea trials, astern revolutions
proval pressure). The sealing efficiency of these                            equal to at least 70 % of the rated ahead rpm for
valves when closed is to be tested at 1,1 pe,zul.                            about 20 minutes

2.2      Casing parts on the exhaust side of low pres-                 During astern and subsequent forward operation, the
sure turbines subjected during operation to the con-                   steam pressures and temperatures and the relative ex-
denser pressure are to be tested at pp = 1,0 bar.                      pansion are not to reach magnitudes liable to endanger
                                                                       the operational safety of the plant.

2     The assessment may be based on ISO 1940-1 standard "Me-
                                                                       2.2     Turbines driving electric generators or auxil-
      chanical vibration – Balance quality requirements of rigid ro-   iary machines are to be run for at least 4 hours at their
      tors" or an equivalent standard.                                 rated power and for 30 minutes at 110 % rated power.