Vibration trips

Safety features such as overspeed trip, low-od trip, remote-solenoid trip, vibration monitor, or other special monitoring of temperature, temperature changes, and casing and rotor expansion... 

Personnel transfers (falls into the water) access by boat access by helicopter Slips and trips Vibration Weather exposure... 

The proteetive system is independent of the eontrol system and provides proteetion from over-speed, over-temperature, vibration, loss of flame, and loss of lubrieation. The over-speed proteetion system generally has a trans-dueer mounted on the aeeessory gear or shaft, and trips the gas turbine at approximately 10% of maximum design speed. The over-temperature system has thermoeouples similar to the normal temperature eontrols with a similar redundant system. The flame deteetion system eonsists of at least two ultraviolet flame deteetors to sense a flame in the eombustion eans. 

The vibration characteristics, determined by use of the instrumentation, will serve as the basis for acceptance or rejection of the machine. API standards generally require that the equipment be operated at speed increments of approximately 10% from zero to the maximum continuous speed and run at the maximum continuous speed until bearings, lube-oil temperatures, and shaft vibrations have stabilized. Next, the speed should be increased to trip speed and the equipment run for a minimum of 15 minutes. Finally, the speed should be reduced to the maximum continuous speed and the equipment should be run for four hours. API does not require that the four hours be uninterrupted however, it is generally interpreted that way. The interpretation is one of the many test criteria to be discussed. It would seem that a break in the test at the midpoint is not the same as having it cut short five minutes from the end because the vendor s boiler took an upset that was not related to the compressor test. The ibration during the shop test is normally specified as the API limit of 1.0 mils peak to peak, or the value from Equation 10.1, unfiltcred. whichever is lower. 

At any speed greater than the maximum eontinu-ous speed, up to and including the trip speed of the driver, the vibration shall not exceed 150 percent of the maximum value reeorded at the maximum continuous speed. 

Before the incident, the facility had experienced a power failure that led to the shutdown of an olefins unit. For several hours, a restart had been attempted and the compressor had tripped on high vibration at low speed. This caused the check valve to close, which placed additional stresses on the valve shaft. Failure to execute a smooth planned start-up was a key contributor to the timing of this incident. However, given the design defects inherent in the valve, an ultimate failure was inevitable. 

At the trip speed of the driver (105 percent for a gas turbine), the vibration should not exceed this level by more than 0.5 mil. 

Eventually, the fouling deposits on the rotor will become so thick that they start to break off, especially if you shut the compressor down for a few hours for minor repairs to the lube-oil system. When the compressor is put back on line, bits and pieces of grayish salt break off, and unbalance the rotor. At 8000 rpm, the high-vibration trip cuts off the fuel to the gas turbine, and the machine is taken off line for repair. 

Compressors also have vibration trips. These trips measure the amplitude of the vibrations—which, if they become excessive, will shut off the fuel, steam, or electricity to the compressor s driver. 

Vibration monitor and overspeed trip on large-scale rotating equipment... 

Test running of compressors and drivers, making vibration trip, governor, and safety device checks, and any other operating tests and adjustments as required. 

Dissolved air is not readily drawn out of solution. It becomes a problem when temperatures rise rapidly or pressures drop. Petroleum oils contain as much as 12% dissolved air. When a system starts up or when it overheats, this air changes from a dissolved phase into small bubbles. If the bubbles are very small in diameter, they remain suspended in the liquid phase of the oil, particularly in high viscosity oils. This can cause air entrainment, which is characterized as a small amount of air in the form of extremely small bubbles dispersed throughout the bulk of the oil. Air entrainment is treated differently than foam and is typically a separate problem. Some of the potential effects of air entrainment include pump cavitation, spongy and erratic operation of hydraulics, loss of precision control, vibrations, oil oxidation, component wear due to reduced lubricant viscosity, equipment shutdown when low oil pressure switches trip, microdieseling... 

---