This article will look at the reasons why chemical storage tanks fail.

Steel Storage Tank Failure

Chemical storage tanks constructed from stainless steel are subject to failure in two main areas.

1. Steel chemical storage tanks are fabricated with sheets of metal. The sheets are welded together to form the tank. The weld seams are where leaks can occur when the weld quality is poor.
2. In addition, chemical attack can break down the integrity of the metal itself. For example, sulfuric acid can become very aggressive if concentrations are below 93%, resulting in acid etching. Acid etching reduces the structural integrity of the stainless steel tank. The chemical concentrations can then become altered due to improper venting, increased humidity, or different concentrations from the supplier. Visual, x-ray, or dye inspections are recommended to detect leaks in steel chemical storage tanks, paying particular attention to weld seams. 

Fiberglass Storage Tanks

Fiberglass is a multi-layer composite construction with an outer layer of resin. Once the resin layer is compromised with a crack, it typically impacts and compromises the structural filament layer of the tank. Chemicals will tend to find the cracks and expand the leak. In addition, the leak can develop into a catastrophic failure of the tank. 

Polyethylene Chemical Storage Tanks

There are two types of construction of polyethylene both create storage tanks are free of welds or seams:

1. Linear (non-molecular bonded)
2. Cross-linked (molecular bonded)

Linear poly storage tanks have the potential to come apart at the polymer chains. This is due to the lack of molecular bonding and reliance on static attraction to gain its strength known as van der Waals force. Caution must be exercised when selecting this material, as it is designed to be a general purpose material used in many applications from toys to containers. When designing this type of tank it is very important to consider how susceptible it is to crack propagation. The installation of a fitting creates an environment that can lead to cracks, which is why fitting areas need to be inspected for cracks with linear polyethylene plastic tanks. A linear poly plastic tank under pressure or even static load can experience a catastrophic failure, similar to what happens when dropping a gallon of milk that splits apart.

Cross-linked polyethylene chemical storage tanks are covalently bonded or molecular bonded. They are extremely resistant to stress cracks. Just like all chemical storage tanks, special attention must be paid to the mechanical fitting on a cross-linked poly chemcial storage tank. If stress occurs due to over pressurization or hard piping, spider or micro cracks will form. The advantage of cross-linked polyethylene is that it will not catastrophly fail. It will, however, require you to cut the compromised section out of the tank and install a larger fitting or replace the tank. While this may be more costly, the risk of large cracks and catastrophic failure of cross-linked polyethylene storage tanks is minimal.

Storing chemicals safely and avoiding the expense of a chemical leak or catastrophic failure of a storage tank is always a concern. Carefully consider the materials and construction of the storage tank and the chemicals which are being stored.

To explore the advantages of a durable high density cross-linked polyethylene chemical storage tank system for your facility, please contact a Poly Processing storage system specialist.

While sodium hypochlorite is a commonly used chemical, it does present unique storage challenges. Let’s examine the storage considerations and solutions for sodium hypochlorite.

Storage Considerations for Sodium Hypochlorite

Since sodium hypochlorite is an aggressive oxidizer, the opportunity for the chemical to escape the storage tank must be limited. The number of wetted connections and fittings on the side of the tank must be minimized to reduce leak paths which can damage a tank.

In addition to oxidation, sodium hypochlorite is sensitive to transition metals. Transition metals will quickly degrade the chemical and cause off-gassing and even more aggressive oxidation.

Sodium Hypochlorite Storage Solutions

To minimize the potential for oxidation, chemical storage tank sidewall fittings and connections must be minimized. Poly Processing’s innovative solution to minimize bulkhead and traditional sidewall fittings, and reduce potential leaks that develop from oxidation, is the Integrally Molded Flanged Outlet, or IMFO® system. Since the full drain flange is molded into the polyethylene plastic tank, the potential for leaks that lead to cracks from oxidation is minimized. In addition, with the IMFO system, gaskets on the bulkhead fitting can be maintained from the exterior of the polyethylene tank.

The IMFO system also makes full tank draining feasible which allows transition metals to be flushed out of the tank before refill.

An additional Poly Processing innovation for storage of sodium hypochlorite is the exclusive OR-1000 system. OR-1000’s engineered inner surface is made of medium-density polyethylene, specifically formulated to resist oxidation. Its outer surface is made of XLPE, high-density crosslinked polyethylene, for superior strength. The two surfaces are molecularly bound together during the roto-molding process, creating a truly seamless bond between the XLPE and the inner surface of the polyethylene tank.

With the IMFO, full tank drainage is accomplished, and the one-piece molded tank construction minimizes the need for any other sidewall connections. In addition, the OR-1000 minimizes the potential for oxidation to the wetted surfaces of the tank. With this one-two punch, Poly Processing offers the superior storage solution for sodium hypochlorite. Poly Processing is the only company to offer a published warranty for sodium hypochlorite storage systems over one year.

If a five-year published warranty and long tank life makes sense for your sodium hypochlorite storage needs, download the sodium hypochlorite storage system guide for more information or contact a Poly Processing chemical storage tank expert.

There are three ways to change the color of polyethylene tanks: inserting color pigments directly into the mold with raw resin, using a compounded resin that is produced in a controlled environment by a resin manufacturer, or by painting the exterior of the chemical storage tank.  Let’s take a closer look at the advantages and disadvantages of each option for coloring polyethylene chemical tanks. 

Adding a Pigment to Resin: Potential for Issues

Coloring a polyethylene tank by adding a pigment into a virgin poly resin can cause unintended negative results.  Pigments are contaminants at some level and often require heavy metals to discolor resin past its natural color.  Pigment also affects other compounds in resin, such as UV inhibitors or antioxidants.  Therefore, any time you add a pigment post-production to a resin you effectively compromise the overall performance of the end product. 

Also, different colors affect the processing of polyethylene tanks.  For example, certain colors will absorb more heat or reflect more heat in the manufacturing process.  Without a way to properly measure the internal temperature of the cooking cycle, you could potentially vary the manufacturing temperature significantly.  Overcooking or undercooking now becomes a distinct possibility.  This can alter the tank’s performance by affecting the brittleness of the plastic as well as how the plastic responds to environmental factors

Compounded Resins: A Better Solution

Another option for coloring polyethylene plastic tanks is by using a compounded resin.  Compounded resins arrive colored directly from the supplier with the pigment introduced in an earlier phase so it doesn’t compromise the structure of the polyethylene.  Poly Processing only uses compounded resins to color polyethylene tanks as they preserve the reaction and don't affect the catalyst, or peroxide, that allows for cross-linking in XLPE tanks.

Painting a Tank vs. Compounded Resin

Another option for changing the color of a polyethylene tank is by painting the exterior.  Painted tanks have an advantage in that the exterior paint 100% blocks the UV.  A latex paint is recommended and will prevent UV from degrading the polymer over time.  This may be a good option for outside tanks storing chemicals that are highly sensitive to UV and heat, like sodium hypochlorite.

What Color Should I Choose?

Polyethylene has the positive trait of being a poor conductor of heat.  Therefore, with large polyethylene tanks, such as tanks over 6,000 gallons, it will take a lot of energy to raise the temperature of the chemical just from exposure to UV.  Since heat is not a big issue in this case, a black tank might make most sense to block UV rays.  With small tanks or in warmer environments where ambient temperature is high, a few degrees difference may create off-gassing issues with temperature sensitive chemicals.  In that case, a white or lighter colored compounded resin polyethylene tank would make most sense to deflect heat.  With a high ambient temperature and UV exposure, painting a tank, or insulating and painting the insulation would likely be the best solution.  The insulation will provide temperature stability while the mastic paint coating will block all UV exposure to the polyethylene tank.

A Study on the Effects of Adding Pigment

Poly Processing commissioned a thorough study with the Pennsylvania College of Technology on the impact of blending pigment with polyethylene.  To view technical details and results from this comprehensive study, click the button below. 

For questions about coloring polyethylene tanks or to determine what color you should choose for your specific tank application, please contact a chemical storage tank expert.

The Properties of High-Density Crosslinked Polyethylene

A specially engineered resin that crosslinks the polymer chains, XLPE essentially delivers a tank constructed of one giant molecule. As a result, XLPE offers 20 times the environmental stress crack resistance of high-density polyethylene. (HDPE)  While XLPE offers a stronger, more durable product, like all polyethylene certain oxidizers can cause it to become brittle. As a result, an innovative solution is required when storing highly oxidizing chemicals.

The OR-1000™ Solution

Inherently all polyethylene tanks can potentially become compromised when exposed to highly oxidizing chemicals. Overtime any type of normal polyethylene material will become brittle, and cracks and leaks may develop at the weaker points of the tank - around the fittings. Knowing these challenges we set out to develop products to extend the life of our customers' tanks, when storing highly oxidizing chemicals such as sulfuric acid and sodium hypochlorite, a special chemical storage system is required.

OR-1000™ adds a barrier between the oxidizing chemical and the XLPE. The wetted, interior surface of an OR-1000™ system is engineered with a medium-density polyethylene, specially designed to resist oxidation. The lower melt heat index of the medium-density polyethylene preserves a special antioxidant package that protects the interior surface of the tank. The result is the best of both worlds when storing highly-oxidizing chemicals: the superior strength and durability of high-density crosslinked polyethylene of the exterior is seamlessly bonded with a medium density polyethylene interior surface in OR-1000™ that resists the damage of oxidation and protects the XLPE exterior surface.

This delivers a chemical storage solution that offers four times the anti-oxidation. The combination of a robust structurally superior plastic in XLPE when combined with the oxidation repelling properties of OR-1000™ is designed as the longest lasting storage system on the market for highly oxidizing chemicals.

Are you using highly oxidizing chemicals such as sulfuric acid or sodium hypochlorite in your processes? If so, explore the advantages of this innovative bonding of high-density crosslinked polyethylene with medium-density polyethylene. Contact a Poly Processing tank specialist to design a chemical storage solution customized for your needs.

In this video, we'll review how we insulate polyethylene chemical storage tanks at Poly Processing.  The insulation maintains the temperature of the chemical being stored.  We apply two inches of insulation and a coating of industrial grade latex paint as well as heating pads of various T-levels and a redundant thermostat controller box. As with all chemical storage considerations, it's important to start with the chemical you're storing.  Factor in the lowest temperature you'd experience in the storage environment to determine the Delta T required.

Have questions about polyethylene plastic tank insulation?  Contact a Poly Processing chemical tank expert for additional information or to configure a custom poly tank package.

Let’s look at why it’s so important to get your chemical storage system right based on the chemical being stored. 

It Always Starts with the Chemical Being Stored

In order to maximize the operation and performance of the chemical delivery system, and the longevity of the chemical storage tank, the nuances of the properties of the chemicals being stored are used must be carefully considered. The storage tank is the headworks of the system. It is a critical component to the overall process of the use of the chemical. If the foundation of the storage tank is wrong, it potentially leads to serious problems.

If you simply spec out a tank for a bid based on generic factors such as size, material, and capacity within defining the chemical used within the tank, you risk getting non-optimal tank. While a chemical storage tank system matched to the specific chemical usage may cost you 20-30% more initially, you recoup the up-front expense in reduced maintenance and tank replacement.

Also, consider the nuances the chemical properties have on the other component parts of the chemical storage system. Expensive valves, fittings, pumps, and flow meters, all essential parts for proper operation, could potentially be compromised.

A Few Examples of Getting It Wrong

Hydrogen peroxide can be a very volatile chemical. As a result the fittings and connections used in the storage of hydrogen peroxide are crucial. Hydrogen peroxide is also a aggressive oxidizer and a strong irritant, so the proper fittings, expansion joints, and venting of the storage system to prevent a fire or explosion and exposure of hydrogen peroxide to employees is vital.

Hydrofluosilicic acid also requires a specialized chemical storage system solution. Hydrofluosilicic acid fumes easily, and the fumes are highly corrosive to nearly all metals. Hydrofluosilicic acid fumes also can quickly etch glass and stoneware. Damage to windows, copper piping, metal electrical conduits resulting from hydrofluosilicic acid fuming can quickly cause thousands of dollars of damage within a building.

Fume tight fittings, overflow fittings, and a proper wetted trap are essential component parts of a chemical storage system for hydrofluosilicic acid.

Get Your Chemical Storage System Right 

Don’t take a risk that could expose people to serious injury, cost you thousands of dollars in property damage, or increase your maintenance and tank replacement costs. Contact a Poly Processing specialist to get the right polyethylene plastic chemical storage tank solution.

Considering the risk of an earthquake on a chemical storage tank, a proper restraint system is essential. Let’s explore steps to take to protect your chemical storage tank in the event of an earthquake.

Evaluate the Earthquake Risk 

It’s vital to determine the possibility of a seismic event at the specific location of the polyethylene chemical storage tank.  Poly Processing uses the latest International Building Code to design restraint systems for polyethylene plastic storage tanks. The actual location and seismic activity are evaluated to make sure safety is ensured.

How Do Polyethylene Tanks React in a Seismic Event

Fiberglass tanks are more rigid and brittle than polyethylene tanks and therefore can’t absorb higher seismic and wind forces.  Polyethylene is more ductile, absorbing the forces and stresses during a seismic event.  As a result, the risk of damage to the polyethylene chemical storage tank is less than a steel or fiberglass tank. 

How a Seismic Tank Restraint System Is Designed 

The size of the polyethylene storage tank, the weight of the fluid, and the type of chemical being stored will determine the restraint system required to prevent damage to the tank during an earthquake. Passive stainless or galvanized steel clips, separate from the polyethylene tank design are used. These clips confine the tank to the area during an earthquake. 

Fiberglass tanks, typically with the clips molded into the tank design, work as long as material structure of the fiberglass tank isn’t compromised. Damage to these structural components can be difficult or impossible to detect on fiberglass chemical storage tanks.

Inspection of seismic restraints is simplified with polyethylene tanks since the restraints are separate from the tank and made of steel. It’s important to visually inspect the steel tank clips and any cables and anchor bolts for corrosion to make sure the restraint system will be effective if it’s needed.

During the 1989 Loma Prieta earthquake in California, over 100 Poly Processing polyethylene storage tanks were located in the earthquake zone. None of the tanks failed. However, while the tanks and seismic restraints held up to the quake, pipes fitted to the tanks cracked and were damaged due to the effect of tank movement on inflexible fittings. Consider flexible tank fittings to help reduce the risk of failure in the complete chemical storage system.

Designing a separate restraint system that functions independently from the tank is the solution to preventing catastrophic storage tank failure in the event of an earthquake. For questions and specific solutions to your chemical storage requirements, please talk to a Poly Processing chemical storage tank system specialist.

What is Fiberglass Reinforced Plastic?

A fiberglass tank is constructed with interwoven glass filaments in a multi-layer construction. The multi-layer starts with a thin resin chemical barrier, followed by the chemical veil (which reinforces the chemical resin) glass filament and a outer weather barrier resin.

Fiberglass Storage Tanks: What Are the Concerns?

Due to the mechanical properties of fiberglass, concerns exist when using fiberglass tanks to store harsh chemicals. While fiberglass reinforced plastic is the material of choice for storage of petroleum-based products such as gasoline and kerosene, it has its faults when storing harsh chemicals where oxidation and corrosion potential exists. The area between the filament layer and the resin is inherently weak in fiberglass reinforced plastic tanks and highly prone to attack from oxidizing or corrosive chemicals such as sodium hypochlorite or sulfuric acid.

Additional concerns with fiberglass reinforced plastic tanks include:

1. Seams - Hand laid in fittings are a major limitation with fiberglass reinforced plastic. Because the fittings are installed after the tank shell is created additional seams are needed in the manufacturing process. The seams are potential weak points in the tanks.
2. More rigid, brittle material - While FRP is lighter than polyethylene or steel tanks, the multi-layered material is more rigid and requires special handling during transportation and installation.
3. Prone to scratching - Scratches to the outer resin layer can compromise the fiberglass tank. Any impact with the outside shell of the tank resulting in a scratch can lead to micro cracking and compromise the tank.
4. Limited UV Protection - While a polyethylene is manufactured with built-in UV inhibitors and storage tank can be manufactured using a Carbon Black resin to provide additional UV protection, the purchaser must specify this option with FRP tanks.
5. Etching of the Glass Resin - Certain chemicals, like Hydrofluosilicic acid can etch the glass and compromise the tank.

The Challenge of Repairing Fiberglass Storage Tanks

Fiberglass Reinforced Plastic tanks are prone to micro-cracks. Given the interwoven strands of the glass layer used in FRP tanks, the origin of the crack is often difficult to locate. As we have highlighted above, the inherent mechanical nature of FRP, micro cracks in the tanks is a serious concern that can lead to tank leaks and potential tank failure and catastrophic exposure. Repairing the entire compromised area when micro cracks develop in fiberglass reinforced plastic storage tanks is virtually impossible. In essence, once a micro crack develops, the storage tank is compromised.

When evaluating your chemical storage options, carefully weigh the advantages a crosslinked polyethylene chemical storage system offers for storing harsh and corrosive chemicals (see FRP vs. PE Tanks Comparison). Crosslinked poly storage tanks minimize expensive maintenance and repairs and reduce the risk of catastrophic tank failure.

Contact a Poly Processing polyethylene chemical storage system specialist to learn how a crosslinked polyethylene storage tank offers increased peace of mind vs. a FRP storage tank.

This article will explore solutions to protect outdoor polyethylene storage tanks from UV damage.

How Ultraviolet Exposure Effects Poly Storage Tanks

Extended exposure to sunlight radiation and in particular ultraviolet rays results in weathering of polyethylene storage tanks.  Without proper treatment, the higher energy spectrum of the UV light causes a compound breakdown of the polyethylene elements, resulting in the polyethylene tank material becoming brittle. This can cause micro cracks leading to leaks and potential failure of the poly chemical storage tank.  For additional information about the impact of ultraviolet light exposure on various resin colors, please refer to the Poly Processing test within the Technical Bulletins under Carbon Black & Plastics.

Solutions to Reduce the Risk of Polyethylene Tank Exposure to UV

Several solutions exist to minimize the potential of UV light when polyethylene storage tanks are stored outside.

1. Carbon Black Resin - Carbon Black is a nearly pure, elemental carbon.  When used as a resin in the molding of the polyethylene tank, it acts as an absorber of UV light.  Adding Carbon Black is a simple, inexpensive solution to creating an internal stabilizer to the poly tank.  When outside, the UV energy is absorbed, transformed into heat, and dissipated throughout the tank.  While Carbon Black polyethylene tanks tend to have higher temperatures than lighter colored or white polyethylene tanks, the UV protection outweighs the effects of the increased temperatures.  Carbon Black is the preferred pigment in higher-end applications, especially when storing harsh chemicals such as sodium hypochlorite.

2. Paint the Tank - Painting the polyethylene tank also adds UV protection. An acrylic house paint, that expands and contracts with the tank, is recommended.  Please refer to the Poly Processing Technical HowTo Bulletin on surface preparation for painting poly tanks.

3. Insulation Coating and Paint - A thin layer of insulation to control heat absorption and a coat of acrylic paint is another solution to protect against UV ray damage to the poly storage tank.

Additional Considerations Regarding The Impact of UV on Polyethylene Tanks

The cycle times, how frequently the polyethylene tank is emptied and filled, and the number of sidewall fittings on the tank, increase the potential for leaks and tank failure. Microcracks will tend to form where the tank is the weakest, at the tank fittings.

One solution to minimize the number of sidewall fittings and reduce the potential for microcracks is Poly Processing’s Integrated Integrally Molded Flanged Outlet or IMFO® system.  With IMFO® chemical storage tank solutions, the flange is molded into the tank itself, eliminating sidewall fittings.

For questions regarding outside polyethylene storage tanks, or for a custom storage tank system solution, please contact a Poly Processing storage tank specialist.

Neutralization

Neutralization, adjusting the pH levels of wastewater with the addition of acid or base, is common in wastewater treatment. Sulfuric acid, or a base chemical, typically sodium hydroxide,  may be added to the water to achieve pH balance. Both sulfuric acid and sodium hydroxide are highly corrosive and  present serious storage challenges, requiring specialized chemical storage systems.

Removing Solid Particles

To facilitate the removal of solid particles within the wastewater, chemicals such as ferric chloride, polymers, and alum are used to produce positive charges to neutralize negative charged solid particles.. As a result, the solid particles clump together, making removal easier. Since more solids exist in wastewater than municipal water, more chemicals are required for this coagulation process.  To ensure safe storage, ferric chloride, aluminum chloride, and polymers require specialized chemical storage tank solutions.

With recent regulatory changes reducing the amount of nutrients such as nitrogen and phosphates has been a growing area for the use of polyethylene tanks. It is becoming more common to see chemicals like acetic acid and sugar water being used to help provide a carbon source to facilitate this biological process.

Odor Control

The collection and treatment of industrial wastewater results in some unpleasant odors. Chemical treatment is used to control odor at the treatment facility. In addition to activated carbon, wet scrubbers are used to reduce odors.  It’s very common to see sodium hydroxide and calcium nitrate. Hydrochloric acid is also used with in conjunction media in the scrubbers. Hydrochloric acid is extremely pungent smelling and highly corrosive and therefore requires a special storage system solution. Here is more information regarding polyethylene storage tank systems for hydrochloric acid.

Disinfection

To prevent the spread of disease, microorganisms that are pathogens must be destroyed or removed from the wastewater. A common, relatively safe and inexpensive disinfecting chemical is chlorine. Sodium hypochlorite presents several major chemical storage challenges. It breaks down under UV light exposure, tends to contain transition metals such as nickel, iron and copper that accumulate in the tank and create off-gassing exposure, and it aggressively oxidizes. A chemical storage system solution specifically engineered to handle sodium hypochlorite is required.

Sludge Treatment and Removal

Finally, a polymer chemical may be used to remove water from the sludge to reduce volume, making transporting the sludge to the landfill easier and less expensive. 
 

Proper use and storage of chemicals during these five stages of the wastewater treatment process is a must to protect injury to water treatment plant workers, the public, and damage to property and the environment.

For your specific wastewater treatment questions, and to design a chemical storage system for your wastewater treatment facility, please contact a Poly Processing chemical storage system specialist.