Choosing Expansion Joints for Power Generation

Expansion joints are used in various types of power plants including fossil fuel fired, hydroelectric, geothermal, waste-to-energy, biomass-to-energy and nuclear installations. They are integral to cooling systems, boiler systems, pumping systems, and any piping system that operates at high temperature and pressure ensuring safety and optimal operation. Typical power generation functions using expansion joints include water cooling, condensers, feed pipelines, steam and air systems, exhaust ducts and areas requiring penetration seals.

Types of expansion joints used in power generation.

Rubber spool-type:

These rubber expansion joints are often used in the pumping system that pushes circulating water throughout the facility. Circulating water pumps pull water into the combined cycle power plant where it is boiled to create steam, which then turns the turbines. The steam returns to the condenser to transform back into water which is then recirculated. These rubber expansion joints will be found near the recirculating water pumps, the condensate pumps, and the condenser connections and cooling towers.

A typical example is the Proco Style 231 spool type rubber expansion joints used for the absorption of directional movement, vibration, noise and shock.

Rubber Piping Expansion Joints:

Rubber expansion joints offer high flexibility, they are also cost effective, corrosion resistant and easy to install. They are often used in power generation applications due to their flexibility, vibration isolation, and corrosion resistance in systems handling water, steam, or other fluids.

A typical example is the Proco Style 240 molded single-sphere rubber expansion joints used for the absorption of directional movement, vibration, noise and shock.

Fabric Ducting Expansion Joints:

The PROCO Series 520,  Series 530, and Series 540 non-metallic connectors are designed to match inlet and outlet flanges between anchor points or next to mechanical equipment such as fans, blowers, compressors and hot air ducts. They are available in U, Arch and W-Designs.

The U-Type integrally flanged non-metallic connector is manufactured in both round and rectangular shapes and found in applications where large movements are required and where vibration and sound absorption are needed. The Arch-Type is found in applications where large movements and short overall lengths are required whereas the W-Type is found in applications where large movements are required for standard hot air/gas service.

PTFE Expansion Joints:

Within environments that require a non-reactive material, moulded PTFE or PTFE lined rubber expansion joints can withstand extreme temperatures, ranging from -200°C to +260°C. With low permeability, PTFE also helps prevent leakage. They offer excellent chemical resistance and low friction, making them ideal for deionized water systems. 

Braided Pipe Connectors:

Use of braided metal connectors for applications such as pumps, compressors, and other mechanical equipment enhances the overall operation of the system by controlling vibration, reducing noise, relieving stress, compensating for potential misalignment whilst withstanding higher operational temperature and pressures.

Flexible metal hose by itself, when subjected to high pressure can over-extend past the ability to operate properly. It is necessary, therefore, to include an external flexible restraint (i.e., braid) to withstand the specified internal pressure and prevent excessive elongation.

Braid, (woven metal) is designed to fit snugly over metal hose and is fastened to the ends of both hose and fittings. The braid is designed to be strong enough to withstand elongation for the full pressure rating of the hose. Common materials used for braided flexible metal connectors are 321 stainless steel hose and 304 stainless steel.

These connectors are made from a variety of different metals, including copper and stainless steel, to suit pumps, compressors and other heavy equipment. Proco Products design and manufacture braided pipe connectors which support the internal hose to withstand pressure whilst allowing necessary movement. 

Pipe Penetration Seals:

Pipe penetration seals provide a robust, watertight seal for pipes passing through walls, floors, or tanks, ensuring efficient system performance and helping to prevent air leakage, water infiltration and fire spread when installed and maintained properly. An example for use in power generation is the top and bottom of the heat steam recovery generator (HSRG) where the pipes grow from thermal expansion

PROCO’s PEN-SEAL Pipe Penetration Seals achieve an efficient, low-cost mechanical seal between any electrical conduit, concrete, cast iron, steel, copper, or pvc/cpvc pipes passing through walls, floors, tanks, pipeline casings, and vaults.

The PEN-SEAL, while being used to seal the gap in electrical conduit lines, will also act as an insulator as well as providing a gas and watertight seal. PEN-SEAL’s standard elastomer material is EPDM, which is suitable for temperatures ranging from -40° F to 250° F. EPDM is suitable for most applications in water—above ground and direct burial—and will provide the electrical insulation where cathodic protection is required.

Silicone material is also available for higher temperature applications up to 400° F. Where the PEN-SEAL may come in contact with Hydrocarbons, Oil, Gas, Jet Fuel, and miscellaneous solvents, a nitrile material is available with temperatures ranging from -40° F to 210° F.

The PEN-SEAL utilizes glass-reinforced plastic for the pressure plates and all hardware is manufactured from steel zinc dichromate. For corrosion resistance, 316 Stainless Steel hardware is also available.

Metal bellows:

Metal bellows expansion joints are designed to withstand high pressures and temperatures, making them suitable for power generation systems. The use of materials such as stainless steel ensures excellent corrosion resistance, suitable for harsh environments. Metal bellows expansion joins are used often within steam turbines, at the crossover and at the turbine to the condenser neck.

Placing Expansion Joints in Power Generation systems

An operational expansion joint relies on anchors, guides, and supports with proper positioning and support crucial for maintaining a maintenance-free system in the long term. Anchoring is necessary for both straight pipeline sections and points where the pipeline changes direction. It’s essential to position expansion joints as close as possible to anchor points. Ensure that piping leading to and from a rubber expansion joint is adequately supported and guided to prevent the joint from bearing the weight of the piping. When specifying expansion joints, consider the following factors:

Supporting Anchors for Pipework
Employing high-quality, dependable anchors capable of withstanding joint pressure thrust and pipe motion forces is crucial. Supplementing anchors with control rods or limit bolts should be placed upstream and downstream of the expansion joints at both ends of the thermally expanding or contracting pipe length. Expansion joints will function without overextending with these full thrust anchors in place.

Calculate Pressure and Temperature
Determine the temperature range and the pressure conditions that the expansion joint will encounter during operation. The “Rule of 250” determines whether rubber or metal expansion joints are appropriate. Rubber expansion joints are preferred if the pressure is under 250 PSI and temperature is below 250° F. Stainless steel expansion joints are typically used for applications with pressures or temperatures over 250, such as steam. In some instances, PTFE or stainless steel is required when pressure or temperature is below 250. This is usually the case for a type of media that is caustic or acidic.

Tips For Storing and Protecting Rubber Expansion Joints

• Use a dry, cool location for storing an expansion joint. Store face down on a pallet or wooden platform without any other boxes on top of expansion joint or expansion joint box.
• Remember when welding near an expansion joint, that splatter can damage rubber material. It is recommended to use a welding blanket to protect against damage.
• It is suggested not to insulate a non-metallic expansion joint however if insulation is required, it should be removable to permit easy access for periodic inspection of the expansion joint material and tightening of expansion joint bolts. Note that insulation could cause restriction of expansion joint movement and heating of the expansion joint material to exceed the maximum rated capability.
• Inspect the mating flanges to ensure that they are clean before installing the rubber expansion joint.

Contact Proco Products for Expansion Joints in Power Generation

Proco Products, Inc. has an inventory of check valves and expansion joints that are suitable for power generation applications and can handle the stresses and pressures that are a normal part of the process. We provide expansion joints for electric power plants, cogeneration and combined heat and power (chp) plants, gas turbine power plants, district heating and cooling systems, diesel engines, turbines, industrial power plants and geothermal power plants. for more information on expansion joints from Proco Products, Inc. and to check pricing and availability, contact us today. 

To find out more about sealing standards, safety, reliability and best practices see Fluid Sealing Association website.