Page 73 - Machinery Component Maintenance

58 Machinery Component Maintenance and Repair

3. Get a sample of coupling grease, if a grease-packed coupling is
used.
4. When removing the coupling, remember to turn the nuts and pre-
vent the bolt head from turning so as to avoid wearing the body-
fitted bolts. In a double-keyed coupling, be sure to check that the
keys are marked as to their location.
5. Be sure to keep the coupling bolts and nuts together as individual
assemblies. Do not plan to reuse the nuts more than twice. If any
doubt exists in this area, a new set of match-weighed nut and bolt
assemblies is cheap insurance.
6. Check and record rotor float within the thrust bearings, and note
also the spacing between shaft ends.
7. Check the total rotor float with the thrust bearing removed, and
note the rotor position relative to the machine case. Check nozzle
stand-off in the case of a steam turbine, or position between dia-
phragms in the case of a compressor.
8. When removing the thrust bearing, be sure to measure and tag any
thrust shims used for thickness and location (inboard or outboard).

Opening the Machine

Before actually opening a major piece of machinery, take time to re-
view the critical steps in the operation. Attempting to remove an upper
half casing without first removing internal (nonexposed) bolting or lift-
ing the casing without using guide pins can result in a much longer and
more expensive overhaul. Be especially careful when opening lube oil
lines. The loss of a flow control orifice or the introduction of dirt into the
system can cause serious problems during the machine startup.
As the machine comes apart, take lots of pictures, make written notes,
and/or use a tape recorder to document what you see. It’s amazing how
much detail will be lost and how difficult it is to accurately reconstruct
events hours or days-let alone years-after they have occurred.
One major petrochemical company operates four identical 20,000
horsepower steam turbines which, due to a series of blade problems, had
to be opened a total of 31 times in an eight-year period. They recognize
the importance of rotor charts to keep track of rotor movements and
modifications, as shown in Figure 2-18. When the first blade in the first
rotor failed, it was not apparent that they were in for such a lengthy prob-
lem. The rotor movement chart was laboriously constructed from mem-
ory when they were halfway into the program and had added a sixth rotor
to the system (four installed and two spares).