Applies to all GE gas turbines
Relates to: If I Owned a Gas Turbine and Liquid Fuel Test Rig
Subject: Functional Testing After Modifications to Gas Turbines

Suppose you are charged with making a modification to an existing GE gas turbine. When completed, the gas turbine should function better than it did during previous operation. Better yet, operation should be significantly improved. Otherwise, why bother?

All too often, when a change is made other problems arise. However, these problems should never be a result of negligence on the part of those charged with the responsibility of upgrading the unit.

At General Electric, there is a group called Conversions, Modifications and Upgrades (CMU). The CMU group offers opportunities to gas turbine owners/operators (GT O/O) to make changes to improve operation, to modify units or to upgrade performance. They come to GT O/O in the form of technical information letters (TIL) and later, if purchased from GE, in field modification instructions (FMI). These two documents are the catalysts for change and improvement. Look at it this way: if GE had had the technology back when the turbine was built, or just “known better,” they would have incorporated these suggestions in the original design.

It would be wise to heed a principle I learned back as a trainee on the GE Gas Turbine Start-up Program (GTSP) from the late engineer George Kennedy:

“Always functionally test the gas turbine after making a change!”

Sure, this seems obvious. However, following this suggestion before you restart the gas turbine is not always done. The way to look at it is this: even if the turbine was malfunctioning before the change was made, the original GE design and operation worked!

Charlie Pond, of PAL Turbine Services, LLC rightly promoted: “taking baby steps” as you bring a gas turbine back on line. There are specific suggestions that were first mentioned in the Turbine Tip: If I Owned a Gas Turbine.

Test, check and simulate some more.

Here is a good example: For early Speedtronic™ Mark I and II gas turbines, the GE Calibrator is a device that can be used to “simulate” operation, as well as to calibrate the panel. You can “dummy in” such signals as turbine speed (NHP), average turbine exhaust temperature (TTX) and voltage to pressure transducer (P2) to simulate the operation of the turbine while still at rest. See photo below:

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Fig 1: Dave Lucier simulates the gas turbine start-up using GE Speedtronic™ Calibrator

When you feel you have adequately tested, checked and simulated gas turbine operation after making a TIL or FMI change, you may be ready for start-up. You should use audio communications with someone placed at the turbine panel ready to push the 5E emergency trip pushbutton. Also, when you are out on the turbine deck and “firing” the turbine, have someone near the hydraulic dump valve with earphones, so a “trip” signal could immediately trip the stop valve to shut off fuel.

Finally, use your human senses: Look, listen, smell and touch (tasting is never necessary). Substitute the last one with a Sixth Sense. Call it Intuition. Never assume anything is right until you prove it to yourself that the turbine is safe to operate.

Below in Fig. 2, an original Roper flow divider is installed on a MS5001P. Notice the rigid tubing for the 10 flow elements and the pressure taps that go to the selector valve and pressure gage.

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Fig. 2: Original flow divider with rigid stainless-steel tubing

In Fig. 3 below, special braided high-pressure hoses are used with the new flow divider. The flexible hosing eliminates any stresses on the new flow divider due to mismatching of tubing connections. Roper flow dividers require installation in a “strain-free” condition. Also, the system must be bled of air and a digital voltmeter can be used to measure fuel flow when testing. Refer to Turbine Tip: Liquid Fuel Test Rig for suggested testing techniques.

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Fig. 3: New Flow Divider with high-pressure flexible hoses on MS5001P

Contact David Lucier of PAL Turbine Services, LLC for more suggestions on how to test, check and simulate operation of gas turbines after changes are made to avoid mistakes.