Expansion joints are extremely important because they allow for the accommodations of temperature changes. Changes in temperature can cause problems or destruction. This article will discuss some of the basics of expansion joints.
Types of Expansion Joints
Types of expansion joints include:
- Piping Expansion Joints
- Flue Duct Expansion Joints
- High Temperature Expansion Joints
- Metal Expansion Joints
Types of Movement
Types of movement include:
- Axial Compression
- Dimensional shortening of the expansion joint face-to-face gap parallel to its longitudinal axis.
- Axial Extension
- Dimensional lengthening of the expansion joint face-to-face gap parallel to its longitudinal axis.
- Lateral
- Inlet and outlet flanges are dimensional displaced perpendicular to its longitudinal axis.
- Torsional Rotation
- Twisting of one end of the expansion joint with respect to the opposite end of the expansion joint about its longitudinal axis.
- Angular Rotation
- Movement that occurs when one flange is moved to an out-of-parallel position with the opposite flange.
- Vibration
- Small, rapid movements back and forth which can occur in any combination of planes.
Typical Applications
300-LT
- Can be used up to 300 degrees F and 5psig in a wet or dry service
- Neoprene, EPDM or Chlorobutyl rubber
- Woven fabric or knitted wire with single or multiple layers
- Applications include wet or dry scrubbers, precipitators, baghouses and FD fans
- Belt or flanged configurations
400-LT
- Can be used up to 400 degrees F and 5psig in a wet or dry service
- Reinforced with single or multiple layers of woven fabric or knitted wire and constructed using Viton
- For increased chemical resistance, especially in where ammonia slip is expected, additional FEP or PTFE gas barrier can be added
- Applications include wet or dry scrubbers, stack breeching ducts, air heater gas outlets, precipitators, baghouses and induced draft fans
- In the case of the air heater fails for short durations, can withstand temperatures up to 750 degrees F
- Belt or flanged configurations
500-T
- Used in wet or dry service up to 575 degrees F and 5spig
- Zero porosity gas barrier of varying thickness ranging from 5mils-30mils mechanically bonded to the substrate constructed from fiberglass reinforced PTFE
- Applications include wet scrubbers and paper processing liquors
500-HT-1000-HT
- Can be found on economizer outlets, secondary air, SCR inlets and other hot flue gas applications
- Requires flow liner and should not be insulated externally unless temperature is below 500 degrees F
- For use in high temperature or gas applications: without insulation pillow-up to 740 degrees F and 2psig, with an insulation pillow-up to 1000 degrees F
- Made from multiple layers based on design temperature requirements
- Utilizes components including: gas seal, insulation, woven fabric and possibly knitted wire
- Several different materials can be used to construct the gas barrier including: EPDM, Viton, PTFE or metal allows based on design conditions
1200-HTG
- Specifically designed for gas turbine applications where temperature is above 1000 degrees F and radial growth, heavy cycling and large movements are expected
- Designed to proved long life, easy installation, low external temperatures and reduced noise
- Found on GT exhausts, HRSG inlets and other high temperature applications
Environmental Controls
One of the most challenging applications for expansion joints is flue gas desulfurization. Due primarily to the “wet” atmosphere found at the inlet and outlet locations and the possibility of pressure fluxuations caused by stack draft, the nature of the process is essentially harmful to most of the common expansion joint designs.
Most expansion joint designs include a cavity that often fills with acidic liquid. This liquid penetrates the edges of the flex element almost immediately. It then slowly begins the process of degrading the bond between the reinforcement plies and the elastomer. This will cause inner ply of the flex element to eventually bubble and separate from the reinforcement layer, thus weakening the tensile strength of the reinforcement layers. Ultimately, this leads to the expansion joint being completely deteriorated even with a drain plug for removing the liquid.
The development of a product suitable for long-term use has been developed for use in this harsh environment. This specially designed FGD flex elements uses a robust Viton outer flex element resistant to aggressive acids and proven to fight against pressure shifts up to 5psig along with PTFE barrier of zero porosity acting as an inner gas seal. This combination of advanced materials will assure long life and predictable performance.
Source: 