As you know that GE recommends a Major Inspection of Heavy Duty Gas Turbines every 48000 hours. We have GE Frame 6B Gas Turbines for which I'm working on optimizing the Instrumentation scope of Major Inspection. The main idea is that we should utilize the Major Inspection in a way that shall ensure minimum number of corrective jobs and equipment failures before the next Major Inspection.
In this regard, shall we go for replacement of the following instrumentation in every MI:
1) Exhaust Thermocouples
2) Wheelspace Thermocouples
3) All Vibration Probes (Radial, Axial, Accelerometers, Seismic)
4) Both GCVs
Please provide your valuable inputs in order to help me out to develop a good optimized scope.
Firstly I would look at the criticality of the machine and secondly the cost. It is also to look at the machine component failure history.
Sure Exhaust and wheelspace T/Cs will fail but, how many and how often. I tend to look more at points of failure and try to eliminate. For sure to change all you listed would make you feel good but the costs and time involved would not make your managers too happy! Many people do change Fuel and IGV servos whether good or not. Do you really have many problems with vibration probes that you want to replace all?
I think I would rather check than replace except for low cost items. Wheelspace T/C are probably the only item on your list that I would say OK replace.
But machine criticality is still the Major driver. If down time is extremely costly then that should mainly drive your judgements.
Please reply and explain
Thanks a lot for your response. This is a Power Generation machine which is coupled with an HRSG. We are very tight on our power and steam requirement and taking a machine shutdown means we can face shortage in terms of power as well as steam. Therefore, shutdown of a machine is really a concern and we want to avoid it as much as possible.
In this circumstance, I wanted to establish a clear and authentic scope which helps us in our cause of running the machine smoothly till next MI.
The issue with thermocouples and probes are that these elements are always working once a machine is running. Even if you test it today, there is no guarantee that they will be fit for use for the next day even. Now usually for an MI, the machine remains shutdown for a long time around 30-50 days. Dont you think that this shall ensure that we perform maintenance that shall ensure its operation for quite some time in the future.
I look forward to your ideas?