Best practices for steam turbine maintenance and operation

Steam turbine operation and performance require the correct steam pressure at the turbine inlet and high steam quality (steam without condensate entrapment) to ensure high turbine reliability.

05/12/2011


Steam turbine operation and performance require the correct steam pressure at the tur­bine inlet and high steam quality (steam without condensate entrapment) to ensure high turbine reliability. The following addresses best practices for optimal steam system turbine maintenance and operation.

Steam Quality

Steam must be of the highest quality. Condensate entrapment in the steam supply increas­es turbine steam rates, reduces the steam turbine efficiency, and causes erosion of steam turbine components (governor valves, blading, and nozzles). Insulating the steam supply lines and components (valves, casing, etc.) helps prevent steam from releasing latent energy, which causes condensation to occur in the steam system.

All steam supply lines must be properly designed with appropriate condensate removal components, including correctly sized steam line drip pockets and steam trap stations. The steam trap stations must have the proper blow down valves that allow operating personnel to properly blow down the trap at startup and shut down. The steam valves need to be highly reliable, and should adhere to a minimum Class VI shut off.

If steam supply quality is questionable, a mechanical coalescing separator should be installed before the turbine inlet to prevent low-quality steam, entrapped with condensate, from entering the turbine.

Pipe Expansion and Contraction

Steam piping should be reviewed, analyzed, designed, and properly installed to ensure there will be no excessive forces transmitted to the turbine flanges. Steam piping may exert forces from four sources:

  1. Pipe dead weight
  2. Thermal expansion
  3. Thrust
  4. Spring rate caused by different types of expansion joints

Thermal expansion also causes movement of the turbine’s flanged connections, which must be considered during the piping design.

The steam piping must be designed to allow for expansion and contraction of the steam piping. The steam lines must have the correct number of appropriately sized hanger supports. Guides should ensure there are no forces or moments on the tur­bine that exceed the values provided by the turbine manufacturer. If the piping is unable to flex while accom­modating the expansion and contrac­tion, then consider the installation of an expansion device such as a pipe loop or expansion joint.

Low-pressure and vacuum lines are usually large and relatively stiff. It is common practice to use an expan­sion joint in these lines to provide the needed flexibility. If an expansion joint is improperly installed, it may cause a pipe reaction greater than the one which it is intended to eliminate. An expansion joint can cause an axial thrust equal to the area of the largest corrugation times the internal pres­sure.

The force necessary to compress or elongate an expansion joint can be extraordinarily large. Either of these forces may be greater than the limits for the exhaust flange. In order to have the lowest reaction, it is best to avoid absorbing pipe line expansion by axial compression or elongation. If it is found that the expansion joints are required, it is essential that they be properly located and their foundations determined.

Supply and Exhaust Line Sizing

Steam piping must be designed to provide full-line steam pressure at the turbine inlet at full-load capacity. The supply line size needs to be calcu­lated not only for the load, but also to include the pressure drops due to length of pipe and system components, including valves and fittings. Any pres­sure loss in the supply line will affect turbine performance.

The discharge piping exhaust pressure will dictate the required discharge line size. As with the inlet piping, all pressure drops must be taken into consideration. Excessive pressure must be eliminated so turbine performance is not affected.

Typically the inlet and outlet steam piping size will be equal to or greater than the actual turbine connections provided for by the manufacturer.

Improper Installations

An improper installation can cause the following problems:

  • Premature bearing failure
  • Nozzle degradation
  • Blade failure
  • Premature coupling failure

Steam Piping Supports

All steam piping requires support for the dead weight of the pipe. The two types of support commonly used in practice are rigid and spring designs. Both types are designed to support the piping, but not to aid in guiding the pipe for expansion reasons. However, a rigid support can be used to restrict the movement of piping in conjunc­tion with an expansion joint. Typical installations employ anchors, supports, and guides. Each of these components assists in supporting the steam piping, but performs different functions. A detailed analysis should always be conducted to ensure proper weights are supported.

Best Practices

  1. Ensure proper steam quality is delivered to the turbine
  2. Proper expansion compensation
  3. Supply and exhaust line are sized properly
  4. Steam piping needs to be properly supported

For more information, visit www.swagelokenergy.com.

The above material is part of Swagelok Energy Advisors' series of Best Practice papers, authored by Kelly Paffel. Kelly is a recognized authority in steam and condensate systems. He is a frequent lecturer and instructor on the technical aspects of steam systems. In addition, Kelly has published many papers on the topics of steam system design and operation. Over the past 30 years, he has conducted thousands of steam system audits and training sessions in the United States and overseas, which has made Kelly an expert in trouble-shooting actual and potential problems in the utilities of steam. Kelly is a member of the U.S. Department of Energy’s (DOE) Steam Best Practices and Steam Training Committees.



The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
A new approach to the Skills Gap; Community colleges may hold the key for manufacturing; 2017 Engineering Leaders Under 40
Doubling down on digital manufacturing; Data driving predictive maintenance; Electric motors and generators; Rewarding operational improvement
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
The cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Power system design for high-performance buildings; mitigating arc flash hazards
Research team developing Tesla coil designs; Implementing wireless process sensing
Commissioning electrical systems; Designing emergency and standby generator systems; Paralleling switchgear generator systems

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me