Page 369 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

348 Major Process &u@ment Mizintenance and Repair

not gotten into the bearing cavities or other internal parts. Be sure that
the working parts of the governing mechanism are clean and in good
working condition.
It is of utmost importance to see that the turbine casing and connecting
pipe lines are drained properly at all times. During operation, any
accumulation of water cools the adjacent metal and causes distortion
which, if severe, may cause blade rubs or vibration. During shutdown
periods, accumulation of water causes excessive corrosion that impairs
the efficiency of the turbine.
The turbine casings are provided with built-in drains from each zone to
the next lower pressure zone and finally to the exhaust. Orifices are
provided for continuous drainage during normal operation, and hand-op-
erated by-passes-where necessary-for use during starting and shut-
down periods.
Similar drains must be provided from all connecting pipe lines. These
include the steam inlet line. and the atmospheric relief line. On condens-
ing machines, all drains-except from the high-pressure steam inlet-
should connect to the condenser or a vacuum trap because, when starting
or operating at light load, vacuum may exist in the entire back end.
It is the duty of the operators to see that these drains function properly
and to use those which are manually operated during starting and shut-
down periods.
Check the overspeed trip mechanism by means of the hand-tripping de-
vice, and be sure it is working properly. Then reset it. It should be obvi-
ous that this tests only the trip mechanism and does not check the speed at
which the overspeed trip weight actually functions.

Starting

1. Be sure that the oil supply to the turbine is operating. See that am-
ple oil pressure is established at the bearings and in the control
system.
2. See that the turbine casing drains, the extraction line drains, the
gland leakoffs are open, and that the steam line is free of water.
3. Open the exhaust valve.
4. Establish water circulation through the condenser.
5. Open the throttle valve a sufficient amount to start the rotor imme-
diately, then close it and open it again just enough to keep the rotor
rolling 200 to 400 rpm. Listen for rubs or other unusual sounds,
especially when the rotor is rolling with the steam shut off, for at
this time a foreign noise can be heard most easily.
6. Start the condensate pump and operate intermittently, if necessary,
to maintain level.