Keeping aging facilities and equipment maintained is an everchanging task that can jeopardize the goal of maximizing uptime. Years of thermal cycling, vibration or foundation settling can disorient piping or pumps. Piping engineers will use rubber expansion joints to account for these types of challenges in a rigid piping system. Permanent misalignment can set
in after years of operation. The original size expansion joint could no longer be the best fit when it comes time to replace.
Replacing a permanently misaligned expansion joint connection with the original part could lead to reduced service life and/or missed expectations of the new expansion joint. Determining the best way to accommodate this when it comes time to replace the existing expansion joint can have long-term effects on reliability.
On October 26, in Fort Worth, Texas, the Expansion Joint Division will be discussing the activities of the Ducting Technical Committee, which includes reviewing of material properties and specifications and guideline for application and selection. The Piping Technical Committee will discuss the updated technical handbook and educational activities and opportunities. The Division overall will continue their discussion on combining the Ducting and Piping Divisions and goals moving forward, including a membership drive and promotion of the FSA.
Many members of the Fluid Sealing Association (FSA) Non-Metallic Expansion Joint Division and of the Expansion Joint Manufacturers Association (EJMA) feel that expansion joints are the forgotten components of many piping systems. Other piping systems components – flanges, gaskets, strainers, valves, pumps and the pipe itself – seem to get most of the design time.
In many ways, expansion joints are the most important components of a well-designed piping system. They are the “living and breathing” dynamic part of the whole system.
Without well-designed and well-placed expansion joints, parts such as pump nozzles, valve bodies and pipe anchors could face excessive loading and vibrational fatigue. Without proper compensation, thermal growth at elevated temperatures can damage some pipes, reducing their operation life.
It has long been recognized that rubber expansion joints (REJs) provide critical design functions that impact the reliability of the entire piping system. This has led some industry professionals to an overly conservative calendar-based replacement program and others to a somewhat reckless approach based on running equipment to failure.
Maximizing an expansion joint’s functional benefits while minimizing its inherent risk has always been a goal for the industry.
Until recently, end users have addressed this concern by using performance replacement REJs along with best practices for maintenance, reliability and operations (MRO).
The practice of insulating over metallic expansion joints to minimize heat loss in a piping system may be common, but it is not a good idea to follow this same practice with rubber expansion joints.
Rubber expansion joints typically consist of synthetic (oil-based) elastomers (ethylene propylene diene monomer [EPDM], neoprene, chlorobutyl, nitrile or clorosulphonated polyethylene-CSM) combined with polyester or nylon and wire reinforcing that provide pressure-restaining capability.
If an end user were to install a typical rubber expansion joint in a system needing insulation to cover the joint in a “hot” application, that individual must consider the probability of failure resulting from heat exposure.
The criteria for expansion joint selection for fluid piping applications focuses on the expansion joint’s quality, durability and capabilities. To ensure that the rubber expansion joint’s installation provides optimal service life, operators and maintenance personnel must consider specific conditions and take a systematic approach. Piping systems require some degree of flexibility. Inadequate flexibility can lead to a catastrophic, potentially life-threatening system failure, making flexibility an important consideration when selecting an expansion joint.
Elastomeric expansion joints have long been recognized for their ability to reduce noise and vibration and accept fluctuating thermal movements in piping systems. Recent advancements in engineered elastomers and textiles led to the development of expansion joints with improved performance and operating life. Equally valuable is their unique ability to be installed in offset and misaligned applications. These cost saving features have made the expansion joint a pivotal component in replacement and retrofit projects, as well as in new construction.
Nonmetallic expansion joints for piping systems are often neglected when planning ahead for an upcoming outage or standard preventative maintenance plan. They are a product that seems to fall between what
is typically defined as an engineered item and a commodity item. Therefore, there always seems to be a scramble at the time of replacement.
Some important considerations before ordering an expansion joint for replacement should be:
• What is the visual condition of the joint? Is there cracking, leaking, soft spots, etc.?
• What is the age of the joint?
• What are the physical dimensions (face-to-face, angular, lateral or torsional offset)?
• What are the service conditions of the application (media, temperature, pressure and movement)?
These are all important to consider and can be determined by a good field survey. A complete field survey can save money and grief during and after installation, including future down time. Visual examination of the joint being replaced and its length of service provide insight for selection of the best replacement. For example, damage from chemical attack, over elongation and premature deterioration can signal the need for changes in materials or design.