Interactive discussions at CCUG enable users to benefit from the experiences of colleagues

Two of the more insightful open-discussion sessions at the Combined Cycle Users Group’s (CCUG) 2017 Annual Conference, held in Phoenix the last week of August, had plant representatives, somewhat extemporaneously, tell the conference leaders (all veteran plant managers) what they needed help with and what problems might they solve, or at least address, during the meeting.

The following are some of the topics/concerns on the minds of users reported out in the first discussion session:

      • We’re seeing components fail for the first time; thermowells are an example. What are some of the other “one-offs” others are seeing, things not expected?

      • The way we operate is changing. We’re now offline during the peak of the day. We have six-hour minimum runs, instead of 12. We had a control valve split in half. Generally, we’re experiencing more cycling and increased maintenance.

      • Daily cycling is leading to cracking of steam piping, not leaks, but weld failures, valve seats cracking, etc. Strainer baskets are not catching foreign material going to the steam turbine.

      • We are experiencing gas-supply issues, curtailments, and gas compressor issues.

      • We tripped a 7FA offline and borescope inspection revealed fuel nozzle orifices coked up (this is gas-only plant). We had compressor station lubricating oil pouring out of everywhere. Eventually, we replaced five sets of gas-turbine fuel nozzles.

      • We’re having gas supply issues. We added diaphragm valves. We’ve had to step up line pressure because of low flow conditions, and experienced valve failures.

      • Our plant doesn’t have adequate cathodic protection because the original plant designers didn’t think it was needed because we are a desert location. 

      • A big recent problem for us centered on failure of the steam turbine/generator’s transformers. We ran for a month in simple cycle because of it.

      • We’ve had all kinds of different brands of flowmeters for our attemperators. One model split in half. How often should we inspect them? Once a year? We found an obstruction in the liner after a borescope inspection. We got a good look at the 180-deg bend in the hot-reheat attemperator and found liner cracks and leaks in the gaskets between the valve body and attemperator. We must inspect these components often.

During the user discussion session later in the program, new sparing and inventory programs sucked up a good portion of the oxygen. One utility representative spoke about a formal critical-parts risk matrix—including cost, location, turnaround times, potential suppliers, etc—conducted across their combined-cycle fleet. This led to increased inventory, especially for long-lead time critical spares at single-point-of-failure locations.

However, increasing spares adds to the tax burden. Another non-utility combined cycle shares parts with other owner/operators in the area, primarily a competing utility. A third user cautioned that equipment sourced overseas requires that you “document the hell out of stuff.” Just because you specked out an in-kind replacement doesn’t mean you’re going to get it.

The discussion on spares necked down to thermocouples. One plant representative said that often one fails, then you put the installed spare in service, and forget about it. Now the practice has shifted so that the plant immediately orders a new one held as inventory.

Steam bypass valves and systems continue to give users fits. A plant attendee reported that the piston on one of his bypass valves broke in half, and they had to use another unit’s bypass system to get the unit started up. Another participant said bypass valves are now inspected every outage because of Stellite seat failures.

Other miscellaneous points to ponder from the discussion include these:

      • A user reported blowing out the guts of the silencer “more than once.”

      • A plant experienced multiple boiler-feed-pump failures and massive pitting on the pump shaft tied to an O-ring failure.

      • A 3 × 1 plant designed for baseload had to significantly modify its zero-discharge water treatment system, originally designed to accommodate a five-day, 16-hr shift operating tempo. “The plant wasn’t able to run in 1 × 1 or 2 × 1 configurations because of this limitation.”

      • If you operate under a two-starts-per-day regime, you need a robust vibration analysis program, and a vibration specialist, to anticipate when critical components may fail.

      • Test motor breaker open/closing regularly, because internals have a limited defined life.

      • Another plant caught relief-valve and thermocouple issues by implementing a commercially available advanced pattern-recognition software package designed for startup periods.

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