WTUI – Cycles Tracking

2. OEM requires tracking of cycles on LM engines

The term “cycles tracking” got special emphasis in the plant manager’s lexicon about seven years ago when the OEM assigned life limits to hot parts and required owner/operators to track engine cycles—specifically normal start/stop, trip from load, and partial cycles (step change). This followed a somewhat similar directive from the FAA for on-wing engines.

    Goal: To achieve the highest level of operational safety by assuring that design-life limits of critical parts—rotors and disks, for example—are not exceeded. The editors were told by one attendee at last year’s Western Turbine meeting that the requirement to track cycles is specified in engine O&M manuals. Some plants in the fleet are tracking cycles, but others still have no system in place for doing so.

   A panel was put in place by WTUI at the 2011 conference to find out how LM owner/operators were approaching the challenge. There were three participants: Ed Jackson of Missouri River Energy Services, Chris Heiberger of Wellhead Services Inc, and Dan Dowler of Encana Corp.

   Each participant explained the system his plant had developed to track cycles. The approaches differed, but all three of the self-developed solutions achieved the objective by providing the information required. None of the panelists said his plant was replacing parts based on results, but it was obvious to one attendee with considerable knowledge on the subject that this was coming—sooner rather than later.

   The same expert, while commending the plants for their initiative, suggested that the individual approach does not meet the intent of the directive because it’s a fleet issue, not a customer issue. The proverbial fly-in-the-ointment is rotable parts. If the data have no pedigree, he said, you only will know the impact your operations have had on the lives of individual parts.

   A better approach, he continued, might be to have an industry-wide data acquisition and analysis service track parts from plant to plant, machine to machine, and through repair processes. The service provider would alert owner/operators when parts in their machines were approaching end of life.

   Early in 2012,  the editors spoke with Larry Gasaway of Gasaway Engineering who confirmed that GE had added a chapter to its O&M manual on critical parts life management. It says, in part, “Critical life-limited parts are those parts that, should they fail, could threaten the structural integrity of the engine or its package. Stress cycles on gas-turbine parts result from transients of speed and temperature that occur during starts, accelerations, and decelerations. Therefore, life limits are expressed in terms of engine cycles and can be related to normal operational data.”

   GE goes on to say that “cycles must be recorded and tracked for each critical life-limited part.” Plus, “It is the owner’s/user’s responsibility to establish a tracking system to ensure that adequate records are maintained for each critical life-limited part and that no such part exceeds its life limit.”

   Gasaway said there is only one commercially available system for LM users to count and track their cycles. Because most users are still not tracking cycles, he continued, this could leave them open for risk. If a part were to fail, insurance companies would investigate and discover that the user was not complying with OEM guidelines, and that could affect how the insurer handles the claim.

   Tracking cycles manually has its drawbacks. Operators can miss cycles, fallout of the habit of recording them, or calculate them incorrectly. Installing an automatic counter mitigates this risk; it runs in the background and counts cycles automatically. Additionally, it generates reports that can follow the life-limited parts through maintenance cycles, depots, and different owners as it gets repaired and rotated around.

   The cycle counter  offered by Gasaway Engineering is a small computer that can plug into most control systems through an Ethernet port on the control system’s network (Figs 1, 2). It will interface with most control systems and makes the information available as OPC data. Then the computer automatically counts the cycles and makes the raw cycle data available as OPC data.

   An Excel add-in from Gasaway Engineering allows Excel to read the OPC data and manipulate it as desired. As an additional benefit, this system will make other engine parameters available to be read by Excel and it can then be used for still other calculations and reports. Added options can include thrust-balance monitoring, temperature-spread monitoring for fuel-nozzle troubleshooting, and compressor efficiency.

   Gasaway Engineering also can run historical data through its program, to count past cycles. Additional network ports can be installed to interface with other networks to store cycle reports on networked PCs, send the data to other PCs to run the reports from your office, or send the information as OPC data to your DCS for display on HMIs or to be archived with the plant’s existing historian. If the plant doesn’t have a historian, or wants to keep this separate, one can be loaded on this computer to archive parameters monitored by the cycle computer.

   The Gasaway cycles counter was said to be meeting or exceeding expectations on two base-load LM2500s in Southern California and three LM6000s at a plant in the Midwest. CCJ