Valves for Power Plant Steam and Water Applications was Hot Topic on June 2, 2011

The following speakers addressed issues for the various valve applications in power plant steam and water systems:

Don Bowers, Vice-President, Sales & Marketing at Weir Valves & Controls, discussed the challenges of Center Cavity over Pressurization (CCOP) that can cause Pressure Locking (PL) and Thermal Binding. He gave the following advice:

• All valves with two seats are subject to CCOP and/or pressure locking.
• There are a number of methods to guard against CCOP and pressure locking. The utility needs to choose the most effective solution for its plant piping system needs.
• It is the owner’s (or designee) responsibility to identify the potential for CCOP and thermal binding.
• Because of design features, parallel slide valves are not subject to thermal binding.

Ory Selzer, Valve Doctor - Power, Americas at CCI -Control Components, Inc, described the important requirements of severe service control valves, as they apply to steam and water.

Velocity related damage mechanisms are:

• Cavitation damage varies as a 5^th to 6^th power of velocity.
• Erosion damage varies as a 2^nd to 4^th power of velocity.
• Control valve noise varies as logarithmic with mach.
• Vibration is caused by excessive fluid velocities and turbulence.
• Corrosion is accelerated by velocity and fluid turbulence.

Common severe service applications for combined cycle power plants are:

• Main boiler feed pump recirculation
• Start-up and main feedwater regulation
• Turbine bypass systems
• Attemperation and spraywater control
• Auxiliary stem
• Vent valves
• Condensate Recirc valves

Don Johnson of CRANE ChemPharma Flow Solutions & CRANE Energy Flow Solutions stated that pressure locking and thermal binding solutions are important for wedge gate and parallel slide gate valves. Thermal binding is generally associated with a wedge gate valve that is closed while the system is hot and then allowed to cool before attempting to open the valve. In a Wedge Gate the wedge is generally cast and has machined seating surfaces on both sides at an angle of 5° from vertical. The wedge evolved from a solid to a Flex Wedge with the addition of flex slots around its center, thereby permitting the wedge to deform to any body seat irregularities. This feature also reduced the torque requirements in order to achieve shutoff. Thermal binding is more common at high temperature conditions. A wedge type gate valve has a mechanical interference between the gate and the seating surfaces. Due to the difference in expansion and contraction the reopening of the valve might be prevented until the valve and disc are reheated. Parallel sliding gate valves are not subject to thermal binding.

The BIOS, PHOTOS and ABSTRACTS are linked below.

BIOS, ABSTRACTS, PHOTOS - June 2, 2011.htm

The individual presentations are as follows:

·         Valves for Power Plant Steam and Water Applications Webinar - Hot Topic Hour June 2, 2011  (Webinar Recording)

·         Prevention of Valve Center Cavity Overpressurization and Thermal Binding: Key Concerns in Power Plant Design and Operation by Don Bowers, Weir Valves & Controls - Hot Topic Hour June 2, 2011  (Presentation)

·         Severe Service Control Valves by Ory Selzer, CCI Valve - Hot Topic Hour June 2, 2011  (Presentation)

·         Pressure Locking & Thermal Binding in Wedge Gate & Parallel Slide Gate Valves by Donald Johnson, Crane Energy Flow Solutions - Hot Topic Hour June 2, 2011  (Presentation)