Page 367 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

346 Major Process Equipment Maintenunce and Repair

sources of external vibration, and has the turbine ready for its overspeed
trip check immediately following completion of the carbon seal ring
break in. Note, however, that a solo run turbine is quite different ther-
mally from a coupled fully-loaded turbine at the same speed. This differ-
ence must be accounted for during carbon packing break-in.
Carbon Break-In Procedure

1. Heat the lubrication oil to a minimum of 100°F before beginning
slow roll. Running oil temperature target is usually 110-120°F.
Mount dial thermometers on the gland seal housing, mid-turbine
case and exhaust casing. These temperatures are used to determine
the steady state temperature point of the turbine prior to slow roll.
2. Open all case drains, trip and throttle valve and steam line drains
leading to the turbine and begin slowly admitting warm-up steam.
Do not start slow roll until the turbine is hot. Larger condensing
turbines, particularly partial admission turbines, may require a spe-
cial manufacturer’s recommended startup procedure to avoid local-
ized rotor bowing.
3. Slow roll at 500 rpm at least one hour. Open sealing steam line and
establish 5-8 psis pressure.
As the turbine gets hotter or the vacuum increases, it will speed
up rapidly using the same steam flow due to the increased availabil-
ity of energy.
4. Close case drains as appropriate.
5. Record vibration readings at both ends of the turbine.
6. Raise the speed to 1 ,OOO rpm and immediately record vibration lev-
els. Stay at 1,OOO rpm for one hour minimum. At about 1,OOO-
1,200 rpm, the bearing’s oil film is carrying the rotor and the shaft
has established a reasonably stable orbit in the bearing. Assuming
that the rotor has relaxed its thermal bow, the “first” reading you
will get at 1,OOO rpm is primarily residual rotor unbalance. After
about 15-30 minutes, you will observe an increase in vibration
(about .25 to 1 mil). Gradually the vibration will drop nearly back
to the first reading you took at 1 ,OOO rpm. This is what you’ve been
looking for; a slight carbon seal ring rub followed by a return to
steady state.
7. Raise the speed to 3,500 rpm in 500 rpm increments, repeating the
sequence of immediately taking “new speed” steady state vibration
levels and watching for the vibration increase and decrease cycle
caused by the carbon rings breaking in.
At about 2,500-3,500 rpm, the new carbons are fairly well
glazed and nearly run in. This is also the point where most people
destroy their packings by assuming that the job is complete.