MORE TOPICS | Expansion Joints
Expansion Joints in Pump Stations
What field surveys reveal about failure and service life.
Eddie Enright | Proco Products
| IMAGE 1: Expansion joints in a deep well pump station (Images courtesy of Proco Products)
Expansion joints in pump stations are small components compared to the pumps, motors and valves surrounding them, but they carry a significant amount of the mechanical stress in a piping system. They absorb thermal expansion and contraction, isolate vibration from rotating equipment and accommodate minor pipe misalignment. In a pump station, each pump typically has one expansion joint on the suction side and another on the discharge side, though configurations vary. A small deep-well station might have only two expansion joints, whereas a larger facility can have a dozen or more spread across multiple pumps.
Field surveys of pump stations are important to prevent joint failure, which can result in leaks or a burst that spews media all over the station. A recent multisite inspection tour across roughly a dozen locations for a Connecticut utility shows the need to treat each site individually. One station was a deep well roughly 60 to 80 feet below the surface with only three pumps and three joints, well-protected from the elements most of the time, except during heavy rain events that sometimes caused the pump station to operate under floodwaters. Others were scattered through residential neighborhoods and had anywhere from three to 10 expansion joints. No two stations are quite alike, so conditions and environment will likely affect the life expectancy of expansion joints differently.
Material Selection & Configuration
Selecting the right expansion joint for a pump station starts with the type of media that is passing through. Chlorination levels and pH affect which elastomer will hold up over time. For typical water and wastewater duty, ethylene propylene diene monomer (EPDM) and neoprene are the most common choices. Nitrile compounds are preferred for sewer applications where petroleum derivatives may be present. More aggressive chemicals or elevated temperatures require polytetrafluoroethylene (PTFE)-lined joints. Do not paint or cover an expansion joint, as it can damage the joint material, hide defects during inspection, trap moisture and interfere with maintenance access.
Configuration matters as much as material. Eccentric reducing joints frequently appear on the suction side of a pump because they promote better flow characteristics into the impeller, while the discharge side more often uses a standard expansion joint style. Eccentric joints also help to prevent cavitation. Movement capability, meaning how much axial compression, extension, lateral offset and angular deflection a joint must tolerate, needs to be matched to the piping layout and anchor points before the joint is installed. Placing the joint near a fixed anchor limits each run to a single axial joint between anchors. Guides then direct movement into the joint itself rather than letting the pipe buckle around it.
Engaging a manufacturer during the design phase, or when reliability engineers become involved, is free and can prevent errors that are expensive to correct.
| IMAGE 2: Expansion joint on the discharge side of the pump
THE 'STAMPED' FRAMEWORK
FOR EXPANSION JOINT SPECIFICATION
Design engineers rely on a structured acronym to ensure complete specification data:
S — Size: Inner diameter, pipe thickness and face-to-face distance between flanges
T — Temperature: Media and ambient temperature ranges, including rate of change
A — Application: Industry, connected equipment, process media, solids content, piping type
M — Movement: Type and magnitude of expected movement at each installation point
P — Pressure/Vacuum: Test, operating and surge pressures
E — End fittings: Fitting type and material (carbon steel, stainless steel 304 or 316), configuration and required drilling pattern (material selection)
D — Delivery: Required lead time for procurement and installation Incomplete STAMPED data is a leading contributor to incorrectly specified joints and premature failure.
What Causes Failure
Expansion joints are designed to fail first to prevent damage to more expensive or critical piping and equipment, but the goal is to avoid failure entirely. Stress and turbulence within the system, the pressure and volume of water moving through it and whether the system was properly anchored can lead to premature expansion joint failure.
Startup surge pressure is a key factor in pump stations, since frequent starting and stopping introduces repeated stress cycles that a continuously running system does not experience.
Installation errors compound these operating stresses. Piping should be aligned before a joint goes in; an expansion joint is not designed to correct misalignment, and offsets greater than about an eighth of an inch can overstress the material well ahead of its expected service life. Where tight spatial constraints make correction impractical, joints can be fabricated with a built-in offset. This requires coordination with the manufacturer, not field improvisation. Tearing near the flange often results from lateral misalignment, overextension or excessive movement.
Install joints at or near ambient design temperature and at their neutral length, with anchors and guides firmly in place before filling and pressure testing. Cracking or tearing near the flange often indicates the joint was overextended or overcompressed relative to its allowable movement range. Inspectors check all of this during an expansion joint survey by measuring the joint’s inside diameter and overall length against its rated tolerance.
Environment plays a role as well. Indoor joints in a stable, temperature-controlled environment can last 15 to 20 years. A typical expectancy for a well-maintained joint in normal service runs seven to 10 years, though the range on either side is wide enough that blanket assumptions are unreliable without an actual inspection. Outdoor installations face ultraviolet exposure and temperature swings that drive thermal expansion in warm weather and contraction in cold climates, both of which shorten service life.
| IMAGE 3: EPDM is a common material used in water and wastewater applications.
Building a Maintenance Program
Regular inspection intervals matter more than any single fix. It is a good idea to have an initial check about a week after commissioning, then follow up with an annual condition assessment conducted by a service provider. Some manufacturers provide this service for free. Facilities that have a preventive maintenance schedule avoid emergency shutdowns and costly repairs.
The most useful outcome of an expansion joint survey is a documented record of every joint in the system: type, size, material, media, temperature, pressure and condition, compiled into a spreadsheet the facility can use going forward. That record gives maintenance staff a reference for future installations, speeds up quoting and lead-time planning and flags custom joints that could take 10 to 14 weeks to replace if one fails without a spare on hand. For facilities running multiple pumps with identical joint sizes, keeping one or two spares on the shelf is a good idea for a quick repair.
Eddie Enright is the eastern regional sales manager of industrial sales for Proco Products. He has over 20 years of experience in the pipe construction, installation and industrial fields. For more information, visit procoproducts.com.
In This Issue
