INTRODUCTION
Information excerpt from
“Inspection and Maintenance Instructions for MS-5001 Gas Turbines Models N, P and R” by
GE Industrial & Power Systems
OPERATING FACTORS AFFECTING MAINTENANCE OF GAS TURBINES
The factors having the greatest influence on the life of parts for any given machine are shown below
• Type of Fuel
• Starting Frequency
• Load Cycle
• Environment
• Maintenance Practices
Fuel
The effect of the type of fuel on parts life is associated with the radiant energy in the combustion
process and the ability to atomize the various liquid fuels. Therefore, natural gas, which does not
require atomization, has the lowest level of radiant energy and will produce the longest life of parts.
Natural gas has been the traditional fuel for use with gas turbines in industrial applications. Limitations
on the available supply of natural gas, with the resultant increase in costs, have led to the
consideration of liquid fuels.
Of the liquid fuels, distillate fuel will produce the next highest life, and crude oil and residual oils, with
the attendant higher radiant energy and more difficult atomization, will produce shorter parts’ life, as
shown in Figure 1-2.
Contaminants in the fuel also affect maintenance intervals. This is particularly true for liquid fuels in
which dirt results in accelerated replacement of pumps, metering elements and fuel nozzles.
Contaminants in fuel gas can erode or corrode control valves and fuel nozzles.
The limiting item to continuous operation on liquid fuels is the fuel nozzles. Exceptionally “clean” fuel
can increase this interval, while “dirty” or ash-containing fuel will decrease it accordingly.
Starting Frequency
Each stop and start of a gas turbine subjects the hot gas path to significant thermal cycles. Control
systems are designed and adjusted to minimize this effect. However, a gas turbine with frequent
starting and stopping requirements will demonstrate parts lives that are shorter than those for a
similar unit in continuous-duty service. See Figure 1-3.
Load Cycle
The load cycle of the gas turbine, up to its continuous rating, will have little effect on parts’ life,
provided it does not require frequent and rapid load changes. See Figure 1-4