Polyethylene chemical storage tanks are made of a flexible membrane. While they are durable and rigid, they also expand and contract with seasonal temperature variations, pressure changes from loading and unloading the tank, and vibrations from pumps during filling and discharge.
Rigid plumbing connections put the tank and fittings at risk of damage, which can cause leaks. You can mitigate this risk in polyethylene chemical storage tanks by installing flexible connections.
Selecting Flexible Expansion Joints for Your Tank
As you design your tank, you’ll need to consider the location of the flexible connectors. The bottom third of the tank sidewall is the most critical area for flexible connectors, because that is where the most movement occurs in a polyethylene tank.
It’s also important to identify the best type of expansion joints for your application. Poly Processing offers two types of expansion joints, the FLEXIJOINT® Expansion Joint and a Flexible Hose Connection.
FLEXIJOINT Expansion Joint
The FLEXIJOINT Expansion Joint is a PTFE in-line flexible connector that accommodates the tank’s expansion and contraction, absorbs damaging shock and vibration, and compensates for misalignment in the piping it feeds.
Note the minimum parameters for connecting an expansion joint on your polyethylene tank:
- Axial Compression ≥ 0.67”
- Axial Extension ≥ 0.67”
- Lateral Deflection ≥ 0.51”
- Angular Deflection ≥ 14°
- Torsional Rotation ≥ 4°
Flexible Hose Connection
Flexible hose connections are resilient, flexible connectors that meet a variety of needs. They can be 3-4 feet long and bend freely to allow the tank to move. These connections are good choices for transitioning through secondary containment and are available in 1” - 4” sizes.
Before Installing Your Flexible Connections
The fittings and accessories are a very important component of designing your chemical storage tank system. Before selecting a flexible connection, there are a few things to consider.
First, you need to have an understanding of the space requirements of your tank system. Flexible hose connections are longer than expansion joints—if you have limited space it’s likely that you’ll need an expansion joint.
It’s also important for your flexible connection to be supported properly, but the support shouldn’t restrict the horizontal plane movement of the tank. A hose won’t flex in a linear outward movement along a straight position, so it must be set up with a bend that uses elbows. When using an expansion joint, the pipe support should be placed after the flex to allow the tank to move outward when filled.
If you’re using flexible connectors, it is critical to ensure you specify them in the correct specifications. Sometimes engineers will specify flexible connectors in the plumbing specs, but we only receive tank specs. We recommend including any flexible connectors that you require in your tank specs as well, so we can see them, do a review on the specs, and design a proper tank system.
Once you’ve selected your flexible connection, make sure you install it in the correct spot. Flexible connectors in most cases only need to be installed on the lower third of the tank sidewall, since this is the section of the tank that moves the most.
Flexible connectors are one of the primary keys to a fully functioning, safe and effective chemical tank storage system that will perform well and last the desired life.