Key Considerations for Designing a Chemical Storage Tank

Proper tank design is crucial to successful safe chemical storage. Purchasing a chemical storage tank isn’t just about selecting the right size — it is vital to design the proper tank configuration for the safety of your employees, the protection of the environment, and to leverage your investment.

Many companies come to us thinking they have a specific chemical storage tank already picked out. As they begin talking with our chemical tank experts, they realize that the tank they had in mind won’t meet their needs at all.

Over the years, we’ve developed a clear process that will help you make all the right decisions about the chemical storage tank that fits your needs. Let’s walk through the steps together.

Step 1: Determine the Chemicals You’re Storing

When designing specifications for a chemical storage tank, many engineers start with size requirements, tank materials, or some other criteria. At Poly Processing, the very first thing we need to know is what kind of chemical will be stored in the tank, and at what concentration. 

This information drives everything else we do in designing your storage solution. Everything about the tank, from the wall thickness to venting structures—even the color of the tank—starts with knowing what chemical will be stored.

If you don’t start by designing for the chemical you’re using, your chemical storage system could be at risk of serious failures, equipment damage, injured personnel, lost product and thousands of dollars in unexpected costs.

Step 2: Identify the Right Tank Materials

Once you understand your chemical’s unique characteristics, you’ll be able to identify the best type of tank materials to meet your storage needs. If you’re storing water, just about any tank will do. If you’re dealing with highly oxidizing chemicals, you’ll need to eliminate certain tank options. 

Let’s take a look at the most common types of tank materials.

Stainless steel storage tanks

Stainless steel tanks can be used for high-pressure, high-volume, and high-temperature applications. Stainless steel storage tanks look nice, too — which is an advantage if your customers will see them. 

Many facilities automatically choose stainless steel simply because the tanks have a good reputation and they are found in every industry. However, that’s not always a wise business decision.

Stainless steel tanks have their drawbacks, especially in cost. In most cases, you can find an alternative solution that’s just as effective, but at three to four times less cost than stainless steel tanks.

Portability is also an issue for stainless steel tanks — once you’ve installed the unit, it’s notoriously difficult to move. There’s also the waiting time — steel tanks often take five months or longer to be delivered.

Fiberglass-reinforced plastic (FRP)

FRP tanks are coated with an interior chemical resin and a structural layer composed of chopped glass fiber or filament-wound fibers and resin. They’re often found in facilities that need to consider tank pressure and volume. 

Many companies purchase expensive fiberglass tanks for applications that FRP solutions aren’t ideally suited for. Harsh chemicals can wick into the tank walls over time, compromising the tank life and requiring early replacement units.

FRP tanks are also more expensive than some other options, and their construction inherently has seams that are vulnerable to leaks — especially if you’re storing aggressive chemicals.

Linear polyethylene

Linear polyethylene is created when a thermoplastic resin is heated to create a fluid plastic. The plastic is hardened and cured into a linear, high-density polyethylene surface. Envision a rope where the individual threads of fiber are mashed and twisted together, but not tied. 

Linear polyethylene is affordable and suitable for storage of benign and non-corrosive chemicals. The lower price point can be attractive, but there’s another cost involved. When a linear polyethylene tank is used to store corrosive materials, the system doesn’t simply develop a pinhole leak — it can fail catastrophically. 

These chemical storage tanks can’t stop cracking once it begins, because the molecular bonds are like a rope of meshed fibers — pull the right way and it comes undone. Eventually, the tank “unzips” itself and the entire sidewall can rip open.

Cross-linked polyethylene (XLPE) storage tanks

Cross-linked polyethylene is high-density polyethylene that is manufactured by adding a catalyst to the thermoplastic resin, which turns it into a thermoset. The catalyst causes a covalent bond that links the molecules together. Picture a chain-linked fence where the metal is welded at the links. 

The result is a plastic that possesses greater impact durability, tensile strength, and resistance to fracture. This makes cross-linked polyethylene an excellent choice when tank integrity is of utmost importance. The chemical resistance, heat resistance, and dimensional stability are unparalleled.

Not only are XLPE tanks safer and stronger than FRP and linear polyethylene, they’re also one of the most affordable solutions on the market. And they have a longer useful life and require less maintenance, increasing their cost value.

When it comes to an affordable chemical tank that can reliably store the harshest materials for decades, it’s hard to beat cross-linked polyethylene.

Tank Design

Once you’ve identified the right tank material for the chemical you’re storing, you’ll need to determine the tank design that will meet your needs. Before you think about costs, consider your floor space, the way that you will use the tank, and any future changes that are likely to affect your storage tanks (e.g., facility upgrades or tank relocation).

Poly Processing offers several innovative tank designs that address specific types of needs.

• Vertical tanks are upright tanks that provide robust containment and dependable service.
• Cone-bottom tanks are generally used in process applications that require total drainage.
• Full-discharge tanks have an outlet valve at the very bottom of the tank, below the tank’s knuckle radius. This gives you a 100% full discharge and makes for safer maintenance.
• Slope-bottom tanks provide full discharge of even heavy substances like sludge and grease. There are no residual materials to clean out.
• Double-wall containment tanks (SAFE-Tanks®) provide a “tank-within-a-tank” solution that reduces your containment footprint and preserves any leaked chemical.
• Open-top tanks are designed for applications that require containment but don’t need everything the SAFE-Tank provides.

Customizations

Finally, your chemical storage tank may require some customizations to meet your application’s needs. We offer two industry-leading options that boost the performance of your storage system.

Poly Processing’s exclusive OR-1000™ system was specifically designed to address aggressive oxidation effects by adding an additional oxidation barrier between the XLPE and the chemical. Its engineered inner surface is made of polyethylene and its outer surface is made of XLPE for superior strength. The result gives you four times the antioxidant strength of any polyethylene on the market today.

PolyGard™ lining system is designed for steel tanks that need the chemical barrier properties of polyethylene. PolyGard is a seamless, corrosive-resistant polyethylene lining system that serves as a barrier between the steel tank  and the chemical it’s storing.

In most cases our customers need fittings and/or accessories installed. The can range from bulkhead fittings, to fill lines, ladders, seismic restraints, tank heating systems, etc. Whatever the need, Poly Processing can help you design your entire tank system.

Chemical Tank Design Made Simple

Finding the right tank is crucial to successful safe chemical storage. It can be easy to design the best tank to fit your needs, if you follow this process. This article provides a high-level overview of the process, but we’ve published an ebook that goes into greater detail to help you make the right decision with greater confidence.

Download our Chemical Storage Tank Buying Guide to identify the right storage system for your unique needs.