Q3 2005

CTOTF tackles user issues on a wide range of aero, frame machines

Program covers virtually all GT models

The defining characteristic of the Combustion Turbine Operations Task Force is that it addresses user issues on virtually all gas turbine (GT) models—aeroderivative and frame— produced by the major manufacturers. That’s why CTOTF (pronounced cee-toff) often is the meeting of choice for plant and asset managers responsible for a variety of engines, especially when time and/or budget constraints militate against attending more than one user group meeting per year. more

Proactive management of GT parts life key to controlling maintenance cost

By Salvatore A Della Villa, Strategic Power Systems Inc

The gas-turbine-based segment of the electric power industry is evolving rapidly , considering most change in the electric sector is measured over a period of decades. Only a few years ago, gas was under $3/million Btu and large combined-cycles were being designed for base-load service. F-class GTs dominated combined-cycle orders and longterm service agreements (LTSAs) championed by the OEMs (original equipment manufacturers) were the risk-mitigation strategy of choice by owner/operators. The plan looked perfect. But then the wheels came off. more

The lowdown on the sticky subject of lubricant varnish

By Greg J Livingstone and Brian Thompson, Analysts Inc

Turbine lube-oil systems have many missions. Among the most important: cooling bearings, flushing contaminants away from rotating parts, preventing in leakage of gases, providing hydrostatic lift for shafts, actuating valves in the hydraulic circuit, and protecting lube-system internals. more

Special workshop explores P91/T91 issues, impending ASME Code changes

By Robert W Anderson, chairman, HRSG User’s Group

Problems in the fabrication, construction, and repair of 9Cr-1Mo steels have surfaced at many combinedcycle stations, raising safety concerns among plant owners and spurring efforts within ASME to revise its Boiler & Pressure Vessel Code. Last July, the HRSG User’s Group assembled several of the world’s leading authorities on P91/T91, including the chairman of the Code-revision Task Group, to discuss the problems as well as the Code changes needed to respond to them (Fig 1). Participants in the well-attended workshop, held in Philadelphia, included O&M personnel, manufacturers, fabricators, EPC contractors, constructors, welders, authorized inspectors, and R-stamp holders from 50 different companies. more

7F Users Group: Focused discussion key to problem-solving

The 7F Gas Turbine User’s Group consistently conducts a superior annual conference. Three things stand out when reviewing meeting notes:

  • User involvement. The 7F is the largest frame user group, with more than 600 active members. Attendance at the annual conference— over 200 user delegates—is double that of the next largest frame meeting. more

501F Users Group: Controls issues, mods dominate conference program

Paul Tegen, chairman, and the steering committee (see sidebar) of the 501F User’s Group deserve high grades for the stimulating program at their annual conference March 28-31 in San Francisco. Program was jam-packed with practical presentations delivered by users and sup­pliers alike. So busy was the schedule that some speakers were allowed only their 15 proverbial min­utes of fame at the podium. more

Frame 6 Users Group: ‘Comeback’ user group gains enviable support

If there were a “comeback award” for user groups serving the gas-turbine-based power and pro­cess communities, as there is in sports, it most certainly would go to the Frame 6 Users Group. This group met annually from 1986 through 2000, but interest waned as the machine matured and users thought most issues had been resolved. Bud­get cuts adversely impacted corpo­rate support and participation by GE Energy, Atlanta, and no meetings were held in 2001, 2002, and 2003. more

And finally, don’t forget the gears

It’s easy to forget about gears. Perhaps that’s why they’re the subject of the last article in the 2006 OUTAGE HANDBOOK. If gears are properly designed and manufactured for the intended service, and installed correctly (think alignment here), they should work essentially problem- free for the life of the plant.

Of course, this assumes that you serve them a steady diet of clean lube oil that meets the OEM’s specifications. more

How to identify, prevent waterside failure mechanisms in your HRSGs

By David G Daniels, Mechanical & Materials Engineering
(www.mmengineering.com)

None of the waterside fail­ure mechanisms found in heat-recovery steam generators (HRSGs)—including flow-accelerated cor­rosion (FAC), corrosion fatigue, thermal fatigue, and under-depos­it corrosion)—are exclusive to this type of boiler. However, failures attributed to these mechanisms have occurred more frequently at some combined-cycle plants than at fossil-fired steam/elec­tric stations. Even relatively new HRSGs have suffered damage. more

Inspecting, maintaining air-cooled generators

It’s not often that you find someone at a gas-turbine-based powerplant do more than shrug his or her shoulders when you ask about the facility’s experience with air-cooled generators. Provide these workhorses clean lube oil and cooling air and they’re a good bet to run forever—in theory, anyway. more

Assessing HRSG dependability

The last thing a plant manager wants is for his generating facility to be forced out of service. This is especially true if the plant is a large combined cycle operating in a competitive market or a gas-turbine (GT)- based cogeneration unit serving an industrial process. The financial penalties for an unexpected outage when under contract to deliver electrical and/or thermal energy can be onerous. Worst case—personnel safety aside— is that one such incident can turn a profitable year into a loss. more

Improve GT operating flexibility, reliability with fuel-system mods

By Mitch Cohen, Turbine Technology Services
(www.turbinetech.com)

Fuel options available to most owner/operators of gas-turbine-based powerplants include natural gas and distillate oil, as well as medium- and low-Btu gases from a variety of sources. Recent fuel-price increases suggest that the ability to switch to more economical fuels in response to price fluctuations is particularly critical in deregulated power markets. more

Identify, correct HRSG gas-side corrosion problems

By Bryan Craig, HRST Inc

Gas-side corrosion affects all heat-recov­ery steam generators (HRSGs). Consequenc­es range from unsightliness and reduced performance to reli­ability problems and potential safety hazards. Presented here are thumbnail sketches of sev­eral corrosion mechanisms that you may find when inspecting your boilers. They explain how to identify the different types of corrosion, the consequences of inaction, problem correction, and when to call for outside assis­tance. In most cases, a relatively small investment is all it takes to assure long life for your HRSG and maximize its availability. more

Maintaining servos to ensure top GT performance

Servo valves were developed to precisely control the pressure of oil flowing to hydraulic actuators responsible for transmitting force or torque to open, shut, and/or modulate valves and other equipment. Before servos, human or mechanical means were used to perform such control functions, but they lacked repeatability and flexibility. In gas-turbine-based powerplants, servos control fuel flow, combustor bypass, compressor bleed valves, NOx control water (or steam), as well as the position of inlet guide vanes and of critical valves on steam turbines in combined-cycle plants. This means they are important to your plant’s performance and safe operation and demand respect despite their small size and seemingly pedestrian function. more

Selecting the appropriate vendor to refurbish parts for your turbines

By Hans van Esch, TEServices (www.TEServices.us)

This is the second in a series of four articles defining the six critical steps to successful refurbishment of industrial gas-turbine (GT) parts. The first two steps, which were presented in the last issue of the COMBINED CYCLE Journal (2Q/2005), covered onsite assessment of component condition and development of repair specifications (access at www. psimedia.info/ccjarchives.htm). This article, Step 3, provides guidelines for selecting the appropriate repair vendors to meet your plant’s specific needs. The third article (4Q/2005) will cover Step 4, the vendor verification process for incoming inspection; the final article (1Q/2006), vendor verification of repairs, coatings, and inspections performed during the refurbishment process of your components (Step 5), and final inspection (Step 6). more