Here is everything you need to know about plastic tanks and their use.
You will learn:
Plastic tanks provide a versatile storage option that is capable of accommodating large volumes of liquids or granular substances. These tanks can be configured in both vertical and horizontal orientations and are suitable for aboveground or underground installation. They may be used as stationary structures or can be easily relocated if needed. Designed to endure prolonged usage, they resist wear, weathering, and any form of deterioration effectively. Industries such as manufacturing, agriculture, and fuel commonly depend on plastic tanks to facilitate the efficient storage and handling of various materials.
Compared to tanks made of steel, stainless steel, or equipped with liners, plastic tanks are both more durable and economical. They offer an inexpensive installation process and, when properly installed, can last anywhere from 20 to 30 years. The lifespan of a plastic tank is influenced by multiple factors, such as correct installation methodologies, the types of chemicals contained within, sufficient venting, and the appropriate selection of pipe fittings.
A variety of methods are employed to manufacture plastic tanks, with polyethylene and polypropylene being the most commonly used materials. Like many plastic products, plastic tanks are typically produced through injection, blow, or rotational molding, with other methods being variations of these primary techniques.
Rotational molding, or roto molding, involves using low pressure and high temperature combined with a mold that rotates on multiple axes to evenly distribute the polymer material. The mold for plastic tanks is a large steel shell designed to the dimensions of the final tank.
In the rotational molding process, polymer material in powder form is first loaded into the mold. The amount of powder used depends on the tank's size and wall thickness. Although color is not a critical factor for most plastic tanks (which are typically white, green, grey, or black), the type of material stored can influence color choices.
The powder and mold are then placed in an oven where heat melts the powder while the mold rotates. As the mold turns, the melted powder coats the surface. The rotational speed and angle, controlled by a computer program, determine the wall thickness. This process takes approximately one to three hours, depending on the tank size.
While continuing to rotate, the mold cools, causing the melted plastic polymer to solidify against the tank walls. This cooling phase generally takes an hour or less.
The method of removing the tank from the mold depends on its size. Smaller tanks can be removed by hand, while larger ones require a forklift or crane. This step is critical, as improper handling can damage the tank. It is done slowly and carefully to ensure the tank's integrity.
Rotational molding is a cost-effective technique compared to injection molding and produces seamless, leak-proof tanks. Any necessary holes or access ports for pipes and fittings are cut into the tank after molding.
Blow molding creates a plastic tank by inflating a molten thermoplastic tube, known as a parison, into the mold cavity. While there are variations in the blow molding process, the core steps involve melting the plastic resin, forming the plastic, and inflating the parison with compressed air. The main types of blow molding include extrusion, injection, and stretch blow molding.
In the extrusion process, plastic resin is fed into a hopper and pushed along by a corkscrew device, which heats the resin as it moves to the blow pin. The plastic material exiting the extruder is then formed into a parison.
The heated parison is placed into a mold and inflated with compressed air. As the air pressure forces the parison against the mold’s sides, it takes the shape of the mold cavity.
In the injection blow molding process, the parison is created in an injection mold and then transferred to the blow mold. Like the extrusion process, compressed air is used to shape the parison within the blow mold.
Stretch blow molding, which is less common for plastic tanks, uses a preform that is heated and then stretched with compressed air to fit the mold shape.
Plastic welding involves three key steps that are somewhat similar to metal welding, but generally easier due to plastic’s pliability and its ability to form a strong, airtight bond. The steps in plastic welding include surface preparation, applying heat with pressure, and allowing time for cooling.
Various forms of plastic welding use different heat methods. This technique is a cost-effective way to repair and maintain plastic tanks. It’s important to note that only like materials can be welded together. Identifying the type of plastic is crucial before proceeding with welding.
After preparing the surface, the next step is to cut a “V” groove along the weld line. Once the groove is made, the welding rod can be tacked into place. The final welding process follows these preliminary steps.
While other methods such as adhesives and fasteners can join plastics, they do not create the same strong bond as plastic welding. The primary advantage of plastic welding is the creation of a tighter, more durable seal that blends seamlessly with the existing material once completed.
The variety of plastic tanks and their designs is vast and continues to grow as engineers discover new applications for them. These designs can vary widely based on their intended use. Some plastic tanks are versatile and adaptable to various conditions, while others are specifically engineered for particular applications.
Plastic tanks can be differentiated by the types of materials used in their production, which include a range of polymers. Material type is one way to classify these tanks. Another classification method is based on their intended use, such as those designed for chemical and fuel storage versus those made for holding grains and solids.
Plastic tanks can also be categorized by their positioning. The tank's placement often provides insight into its intended use and function.
Vertical placement is the most common configuration for plastic tanks because it offers versatility and ease of access for general purposes. These tanks are primarily used above ground due to the thickness of their walls, though they can also be installed in underground chambers made of concrete or brick for additional protection.
Horizontal plastic tanks are designed for transportation and can serve as mobile storage units. They can be either permanently installed or loaded onto the back of a truck or trailer. This design allows for easy access during filling and loading. Their low profile is intended to maintain the vehicle’s center of gravity and prevent disruption.
The primary distinction between above-ground and underground tanks lies in the engineering requirements for underground tanks. These tanks must be more robust and durable to endure the weight and pressure of the surrounding soil. Burying tanks serves several purposes: it conceals them from view, provides additional space, offers protection from vandalism, and helps meet environmental regulations. Manufacturers of underground tanks provide specific installation guidelines that must be strictly adhered to.
Silo or conical tanks require specialized stands to facilitate the access of contents from their cone-shaped base. These tanks are loaded through a lid at the top and accessed via an opening at the bottom of the cone. The design allows for efficient discharge of materials through the tapered bottom.
Double-wall plastic tanks feature a tank within a tank, providing secondary containment for the stored contents. This design was developed as a safety measure to meet environmental protection standards and prevent hazardous chemical spills. Double-wall tanks may include a dome to protect against rainwater infiltrating the space between the inner and outer walls. They are typically constructed from high-density polyethylene or cross-linked polyethylene, each offering varying degrees of chemical resistance.
Cylindrical plastic storage tanks, made from polyethylene or polypropylene, are resistant to rust, corrosion, UV rays, and certain chemicals. Their strength and stability make them well-suited for applications in the pharmaceutical industry, mixing plants, and liquid storage facilities. These tanks come in both double and single-wall constructions and can be configured as vertical, free-standing units with a flat bottom for both indoor and outdoor use, or as horizontal tanks with leg supports.
Stackable plastic tanks offer a practical solution for organizing fluid inventory and replacing traditional 55-gallon drums. Their lock-and-stack design optimizes floor space, with a footprint of approximately three feet by three feet. These tanks can be securely stacked in any configuration without requiring brackets or specialized racking systems.
Available in various designs, stackable plastic tanks can be used both indoors and outdoors. They come in a wide range of capacities, from 30 to 40 gallons and extending to several hundred gallons, accommodating diverse storage needs.
The design of a plastic tank is influenced by the type of material it will store. Plastic tanks have gained popularity due to their cost-effectiveness and versatility. They are widely used across various industries, including food processing, wastewater management, chemical manufacturing, and agriculture.
In addition to their positioning, plastic tanks are categorized based on the type of polymer used in their construction. Common polymers include polyethylene, polypropylene, and fiberglass.
Polyethylene is a high-quality thermoplastic known for its resistance to weathering, abrasion, and chemicals. Its durability makes it an ideal material for producing plastic tanks. The natural color of polyethylene ranges from white to yellow, depending on the tank's wall thickness. For outdoor applications, polyethylene tanks are often treated with an ultraviolet light stabilizer to provide additional protection against UV degradation.
Polyethylene comes in two main forms: linear and cross-linked.
Polypropylene is a thermoplastic made from propylene monomers. Its low density makes it lighter than many other plastic materials. To enhance its strength, polypropylene is often copolymerized with other polymers like polyethylene. Its key qualities—chemical resistance, elasticity, toughness, and fatigue resistance—make it well-suited for use in storage tanks.
Polypropylene's versatility is due to its adaptability to various fabrication processes. It comes in two main types: homopolymer and copolymer. The homopolymer is the most commonly used, while the block version of the copolymer is noted for its superior impact resistance and strength.
Due to its high chemical resistance, polypropylene is often used to store reactive and corrosive materials. It can withstand operating temperatures up to 212°F, making it suitable for autoclaving. A distinctive feature of polypropylene is its rough, irregular interior surface.
Fiberglass storage tanks are suitable for both underground and above-ground applications due to their durability, corrosion resistance, and resistance to deterioration and weathering. Their impermeability and mono hull construction eliminate the need for additional waterproofing. Additionally, fiberglass is lighter than many other tank materials, making these tanks easier to relocate, install, and transport.
Plastic tanks made from polyethylene and polypropylene offer a cost-effective solution for storing a wide range of materials. Before the advent of plastic tanks, metal containers were the most common choice for storing liquids, grains, and granular materials. Advances in plastic technology have resulted in storage solutions that surpass traditional methods in durability and strength.
Initially, plastic storage tanks were used primarily for water storage for livestock, crops, and irrigation. As polymers became more versatile, plastic water tanks found applications in various other fields.
Plastic tanks have become a popular choice for water storage due to their ability to be easily connected to downspouts for rainwater harvesting or for commercial and industrial water collection. In rural areas, they are crucial for supplementing limited water supplies. The versatility of plastic tanks enables them to store various types of water, including saltwater, distilled water, wastewater, groundwater, rainwater, and melted snow.
Plastic storage tanks are available in various sizes, gauges, strengths, and specifications to ensure the safe storage of chemicals. Their versatility in placement and ability to withstand harsh weather conditions have made them a popular choice for industrial and manufacturing applications. Polyethylene plastic tanks, in particular, are increasingly replacing metal storage tanks due to their resistance to rust, corrosion, and deterioration. These tanks are suitable for storing a range of substances, including fertilizers, pesticides, pharmaceutical products, and various acids such as hydrochloric, sulfuric, sodium hypochlorite, and nitric acid. When storing acids, it's crucial to consider the type of plastic used for the tank. The selection of the appropriate tank depends on assessing the strength and resistive properties of the plastic material.
Plastic storage tanks are ideal for storing fuel and are commonly used at racetracks, factories, and repair garages. The polyethylene core of these tanks can accommodate a wide range of fuels, including diesel, gasoline, butane, and natural gas.
Grain feed bins are designed for storing corn, soybeans, and other granular products. These bins are constructed from UV-treated polyethylene, typically 3/16 inch thick. Plastic storage tanks are preferred for grain storage due to their resistance to rust, corrosion, and weather, issues commonly associated with metal storage units. Additionally, the smooth interior surface of plastic tanks minimizes bridging and eliminates the need for rivets and clogging seams.
Plastic septic tanks have become an option for waste collection because they last longer than traditional methods, are easy to install, and more economical. In most cases, plastic septic tanks are produced using rotational molding so that the final product is seamless in one piece construction. Unlike other septic tank products, plastic septic tanks do not require any form of special coating since the plastic material is capable of withstanding any type of conditions.
One of the key concerns for septic tanks is their reaction to chemicals in the soil and gases from sewage systems. Polyethylene, used in plastic septic tanks, is resistant to both soil chemicals and sewage system gases, addressing these concerns effectively.
Plastic tanks have become essential across various industries due to their durability and capacity to endure harsh and hazardous conditions. As the applications for plastics have advanced and expanded, numerous commercial, governmental, and manufacturing operations have recognized plastic tanks as valuable and cost-effective assets.
Plastic tanks are utilized by a range of groups and organizations, including fire departments, sewage operations, pharmaceutical companies, electroplating manufacturers, and water treatment facilities, among others.
Plastic water tanks for fire pumping trucks are a lightweight alternative to other types of tanks and lessen the load on the truck‘s chassis. They come in a variety of sizes from ones that are 5 gallons up to and including ones that are 5000 gallons. They are lighter than steel tanks and are 90% stronger. In order for tanks to be used on fire trucks, they must be approved by the National Fire Protection Association and adhere to their regulations.
In electroplating, plastic tanks must exhibit excellent chemical resistance to handle strong acids, organic solvents, degreasing agents, and electrolytes involved in the process. These tanks are specifically engineered for their role in electroplating, incorporating features such as racks, bus bars, and other enhancements to meet the industry's rigorous demands.
Plastic tanks used in the pharmaceutical industry must meet stringent standards set by the American Society for Testing and Materials (ASTM) and comply with regulatory requirements from governmental and other agencies. The primary concerns for pharmaceutical tanks are sterilization and cleanliness, which is why plastic tanks are widely used in this sector. They are employed for storing and transporting powders, chemicals, and granular materials, ensuring high standards of hygiene and safety.
Sewer truck plastic tanks are preferred over metal tanks due to their resistance to rust and corrosion, which extends their lifespan and reduces maintenance needs. Plastic tanks are easier to clean and sanitize and are resilient to the chemical effects of wastewater. Their lighter weight and large capacity help minimize truck trips and streamline refuse removal processes.
Degreasing plastic tanks are constructed from durable polypropylene, making them ideal for degreasing operations due to their non-sticky, corrosion-resistant surfaces. Their mobility allows for flexible use in various locations and easy storage when not in use. Unlike metal tanks, plastic degreasing tanks are made as a single, leak-proof unit.
Plastic tanks used in food processing must comply with the Food and Drug Administration (FDA) standards for equipment handling food products. Approval is based on the finished tank, not just the resin used in its production. Even if a resin meets FDA standards, it doesn't guarantee that the final tank will have the same qualifications.
The main challenge for plastic food tanks is ensuring proper drainage to prevent spoilage or rot from residual products. It is crucial that these tanks can be completely drained. Additionally, fittings or access points must be securely sealed to prevent leaks and waste.
Fish farming plastic tanks must adhere to the same FDA standards as tanks used for other food products. These tanks typically feature an overflow system to maintain a consistent water level and include dividers for fish movement. They also come with drop-in baskets and chute systems to facilitate fish transfer.
An essential requirement for fish farming tanks is the inclusion of pumping and filtration systems to ensure the health and safety of the fish, in accordance with FDA regulations.
Plastic tanks are extensively used in agriculture due to their flexibility, durability, strength, and ability to withstand harsh weather conditions. They primarily serve for storing and transporting liquids like fuels, fertilizers, and pesticides. The widespread use of plastic tanks in agriculture is attributed to their safety, ease of handling, and long-lasting performance, meeting the demands of farming operations.
Like any tool, plastic tanks require proper care to maintain their performance. Although they are sturdy and long-lasting, plastic tanks can deteriorate if not regularly inspected and maintained. This is particularly important for tanks in harsh or hazardous environments. Tanks intended for storing volatile or explosive materials need extra attention to ensure safety and environmental protection.
Elevated temperatures pose a significant risk to sensitive equipment, including plastic tanks. Prolonged exposure to high temperatures can drastically shorten the tank's lifespan. The impact of temperature on a tank depends on factors such as the contents, tank size and configuration, construction methods, wall thickness, and support structures.
Assessing the effects of heat on buried tanks is more challenging, but most are designed with adequate insulation to withstand their operational environment.
Thermoplastics not treated with UV protective coatings are susceptible to damage from UV rays. Exposure leads to discoloration and brittleness, which can result in cracking under high temperatures. Manufacturers account for weathering and harsh conditions during construction to ensure tanks meet application requirements.
Polyethylene materials, depending on their type, can be prone to cracking, especially when exposed to certain detergents. Stress cracking is often caused by surface agents like fillers and tie-downs. Choosing the right plastic type and following safety procedures can minimize cracking risks.
The placement of plastic tanks is crucial for their longevity. Tanks on uneven ground or high-traffic areas are more susceptible to stress and cracking. Proper support is essential, whether for transport or stationary use. Care should be taken during loading and unloading to ensure the tank remains balanced and centered.
Installing plastic tanks involves evaluating the impact of surrounding conditions. Tanks should be placed away from potential hazards like falling debris from trees or rocks. Severe weather conditions also require tanks to be designed to handle temperature fluctuations and precipitation without damage.
Plastic tanks vary in design and purpose. While some are versatile, others are purpose-built for specific functions. When purchasing and installing a tank, review the manufacturer’s specifications and limitations to ensure it meets the required temperature and environmental conditions, which can help extend its lifespan.
Regular cleaning is vital for maintaining the effectiveness of a plastic tank. Though often considered for food and chemical industries, cleaning is important for all tanks to ensure they remain in good working condition. Proper maintenance practices can significantly extend the tank's life.
Tanks used in reverse osmosis processes must withstand high pressures. Regular maintenance and inspections are crucial to detect cracks or weak points. Despite the durability of most plastics, checking for deterioration helps ensure the tank performs reliably.
To ensure the longevity of a plastic tank, it is crucial that its piping is connected correctly. When a plastic tank is filled with liquid, the plastic walls expand, which is often not visible to the naked eye. This expansion is more pronounced when storing warm liquids.
If a drain or fill pipe is attached to a plastic tank, it must accommodate the movement of the tank walls during expansion to prevent stress and cracking. The solution is to use an expansion fitting or joint that allows the tank fitting to move freely.The most effective method for handling tank wall expansion and contraction is to connect the plastic tank fittings directly to a threaded plastic hose barb adapter and use a flexible plastic tube approximately 12 to 18 inches long with stainless steel band clamps. A lightweight plastic valve should be installed between the tank fitting and the tube but should not be secured until the expansion fitting is in place, otherwise, the expansion fitting’s purpose will be compromised. Alternative fittings, such as bellows-type expansion joints, can also be used.
Proper piping installation is essential for extending the lifespan and ensuring the durability of a plastic tank.
The lifespan of plastic tanks varies depending on their location. Indoor tanks are shielded from UV rays and, provided they are maintained at ambient temperatures and properly plumbed, can last over 30 years.
Outdoor tanks, exposed to UV rays and extreme climates, typically last about 20 years. To extend their lifespan, outdoor tanks can be covered with roofs or shelters, painted, or fitted with tank jackets. Jackets help protect against freezing and UV damage, thereby extending the tank’s life.
Plastic tanks, used for storing volatile materials, food products, acids, and chemicals, became subject to Environmental Protection Agency (EPA) regulations when they were first introduced in 1988. Initially focusing on metal tanks, these regulations have since been updated to include more specific requirements for plastic tanks.
Underground tanks, which are primarily used for storing fuel and collecting waste, pose significant environmental risks due to potential seepage. Recognizing the environmental hazards associated with these tanks, the EPA has implemented stricter regulations to address these concerns.
For tanks used in the production of food and pharmaceuticals, the Food and Drug Administration (FDA) establishes regulations. These guidelines cover the types of materials used and the design standards necessary to ensure safety and compliance in food processing and pharmaceutical applications.
Regulations for plastic storage tanks by the EPA are categorized into two classifications: Underground Storage Tanks (UST) and Above Ground Storage Tanks (AST). These regulations are governed by the Spill Prevention, Control, and Countermeasure (SPCC) regulations, specifically under 40 CFR Part 112.
The SPCC defines a bulk storage container as:
… any container used to store oil. These containers serve purposes including, but not limited to, storing oil before its use, during its use, or before further distribution in commerce.
Oil-filled electrical, operating, or manufacturing equipment is not classified as a bulk storage container. (from epa.gov/ust)
To aid in inspecting bulk containers, the SPCC provides a fact inspection sheet available on the EPA website. The regulations primarily focus on the storage of volatile materials such as fuels, gases, and chemicals.
The FDA focuses on materials and equipment that will come into contact with food or items intended for human consumption. For plastic tanks used in food storage or construction, the FDA maintains a list of approved resins. Manufacturers producing food-grade plastic tanks strictly adhere to these FDA guidelines, enhancing the credibility and appeal of their products.
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