One of the most important design considerations of any chemical storage tank system is the use of flexible connectors and isolation valves. When paired correctly, these accessories will not only help ensure your storage tank's longevity, they can also protect the tank from hinge points that cause dangerous leaks.
Let's take a closer look at flexible connectors and isolation valves—and at a danger that may be hiding in plain sight.
One of the biggest advantages of polyethylene chemical storage tanks is that they expand and contract with pressure changes during loading and unloading and during changing weather conditions. While a rigid tank is more susceptible to cracking and damage over time, a flexible tank is resilient to pressure.
However, a polyethylene storage tank is only as good as the fittings and accessories you pair it with. For many years, the industry standard was hard piping that came directly into the side of the tank. Because hard piping won’t move with an expanding or contracting sidewall, it can damage a polyethylene tank in several ways:
Flexible expansion joints allow the tank to move as it should while avoiding the damage that rigid piping can cause. However, you’ll also need an isolation valve as a backup feature to prevent loss of product.
It’s also important to identify the best type of expansion joints for your application. Some large linear tank manufacturers tried using common expansion joints on their tanks, but the tanks continued to break at the fitting area. It’s important to use the right type of expansion joint and the right type of tank.
Poly Processing offers the PTFE Expansion Joint.
The PTFE 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.
Flexible Connection Minimum Specifications are below: (For common size fittings and piping systems up to 6”) Contact Poly Processing for information on larger expansion joints.
PTFE (polytetrafluoroethylene) is selected for this application because of its exceptional chemical resistance across a broad range of aggressive chemicals, including strong acids, caustics, and oxidizers. Unlike rubber or elastomeric expansion joints, PTFE will not degrade, swell, or become brittle when exposed to the chemicals most commonly stored in polyethylene tanks. This makes it the appropriate choice for long-term service in demanding industrial environments.
Fittings and accessories are very important components in designing your chemical storage tank system. Before selecting a flexible connection, there are a few things to consider.
First, you need to understand the space requirements of your tank system. What will the total dimension be of the plumbing with the expansion joint and the tank system?
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. 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 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, install it in the correct spot. In most cases, flexible connectors 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.
Correct installation sequence is the single most important factor in ensuring your flexible connector and isolation valve system performs as designed. Follow these steps to avoid the most common and costly installation errors:
Install the isolation valve directly at the tank fitting, as close to the tank wall as possible. This is the first component in the flow path.
Install the PTFE Expansion Joint immediately downstream of the isolation valve. The valve must always be between the tank and the expansion joint.
Install the pipe support after the expansion joint, not before it. The support must allow the tank sidewall to move freely in the horizontal plane.
Verify that the expansion joint is not compressed or stretched during installation. It should be installed in its neutral, relaxed position.
Confirm the full assembly with your Poly Processing engineer before commissioning the system. A pre-startup review can catch misconfigurations before they become costly failures.
This sequence ensures that if the expansion joint ever develops a leak, the isolation valve can be closed immediately to stop the flow of chemical. Reversing the order of the valve and the expansion joint eliminates this protection entirely.
An isolation valve is a valve that stops the flow of chemicals in or out of the tank. It is installed for maintenance or safety purposes, and you should have an isolation valve at key intersections along with the flow of travel. If a leak develops in the piping or fittings, the valve can be closed upstream to prevent further loss. This saves on the chemical costs and the hassle of cleanup and downtime.
An isolation valve is operated by a quarter turn and uses a floating valve for closure. The position of the handle tells you at a glance if the line is open or shut, giving you peace of mind that the valve is sealed. There are several types of isolation valves, including ball valves, single body isolation valves, top entry isolation valves and split body isolation valves.
Isolation valves are also relatively inexpensive. One-piece isolation valves are easy to replace, two-piece versions are easy to clean, and three-piece versions are easy to repair.
Selecting the correct isolation valve body style depends on your maintenance priorities and the nature of the chemical being stored:
|
Valve Type |
Best For |
Key Advantage
|
|---|---|---|
|
One-Piece (Single Body) |
Low-maintenance, standard applications |
Lowest cost; easiest to replace |
|
Two-Piece |
Applications requiring periodic cleaning |
Can be disassembled without cutting the line |
|
Three-Piece |
High-value or aggressive chemical service |
Fully repairable in place; longest service life |
|
Top Entry |
Tight spaces or in-line maintenance |
Serviceable without removing from the pipeline |
For most chemical storage applications involving aggressive or high-value chemicals, Poly Processing recommends a three-piece isolation valve. The ability to repair the valve in place, rather than replacing it, reduces both downtime and long-term maintenance costs.
Improperly installed valves and expansion joints can put your chemical tank at risk. If a leak occurs at the joint, you won’t be able to shut off the flow and you will lose good product.
Our field service teams have seen several examples of improper installations at customer sites. In each case, the facility was confident that they were protected and safe. However, their configuration put them in danger of unnecessarily losing a great volume of product.
For a flexible connector to serve its purpose, it has to be installed correctly and supported properly. The problem arises when some customers place the expansion joint between the fitting and the isolation valve. The purpose of the isolation valve is to shut off the flow if the expansion joint starts to leak, but when the valve is placed after the expansion joint, there is no way to shut off the flow. In this case, a failure in the expansion joint will be unstoppable and the entire contents of the chemical tank can be lost—simply due to improper installation.
The financial consequences of this single installation error can be severe. Depending on the chemical stored, the cost of a full tank loss can range from thousands to tens of thousands of dollars in product alone, before accounting for environmental remediation, regulatory fines, facility downtime, and personnel safety incidents. A correct installation costs nothing extra. An incorrect one can cost everything.
You can rely on Poly Processing to help ensure that your flexible connectors are properly installed and functioning as intended. Contact us to arrange for an on-site inspection or send us your questions about flexible connectors. Talk to a chemical storage expert today.