Here is everything you need to know about plastic tanks on the internet.
You will learn:
- What is a Plastic Tank?
- How Plastic Tanks are Made
- The Types of Plastics Used to Make Plastic Tanks
- Industries that Rely on Plastic Tanks
- And much more…
Chapter 1: What is a Plastic Tank?
A plastic tank is a large capacity liquid or granular storage unit that can be vertical, horizontal, below or above ground, as well as movable. They are designed to hold several gallons of a variety of substances for long periods without experiencing wear, weathering, or deterioration. Manufacturers, farmers, and fuel companies depend on plastic tanks as a means of transferring and saving materials for later use.
The lifespan of a polyethylene tank is between 15 and 20 years or longer. Chemicals stored, proper installation, venting, and types of pipe fittings are major factors that determine a tanks lifespan.
Chapter 2: How Plastic Tanks are Made
There are a wide variety of methods used to produce plastic tanks with polyethylene and polypropylene being the most common raw materials. As with most plastic components and parts, plastic tanks are produced using injection, blow, or rotational molding with other methods being variations of these common ones.
How Plastic Tanks are Made
Rotational Molding –
Rotational or roto molding uses low pressure and high temperature combined with a mold that is rotated at multiple axes to evenly distribute the polymer material. The mold for plastic tanks is a large steel shell at the dimensions of the final tank.
The first step in the rotational molding process is to load the polymer material in powder form into the mold. The amount of powder depends on the size of the tank and its wall thickness. In the case of plastic tanks, color is not a critical factor since most tanks are white, green, grey, or black. A factor that has to be considered regarding the color of the tanks is the type of material that it will store.
Tank Oven –
The powder and mold are placed in an oven, where the heat slowly melts the powder as the mold is rotated in the oven. As the multiaxial mold turns, the melted powder coats the surface of the mold. A computer program controls the rotational speed and angle to achieve the desired wall thickness. The process takes approximately one to three hours depending on the size of the tank.
While still rotating, the mold is allowed to cool as the heat is slowly removed. As the mold cools, the melted plastic polymer solidifies against the walls of the tank. This aspect of the process takes an hour or less.
Molded Tank Removal –
The method for tank removal is dependent on the size of the tank. Small tanks can be removed by hand while larger ones require a forklift or crane. This part of the process is critical since mishandling can lead to damage to the tank. It is completed slowly and carefully with the greatest amount of care.
Rotational molding is less expensive compared to injection molding and produces one piece seamless, leak proof tanks. Holes in the tank or access ports are cut into the tank for the addition of pipes and fittings.
Blow molding forms a plastic tank by inflating or blowing a molten thermoplastic tube, parison, into the two halves of a mold cavity. Though there are variations in the blow molding process, the common factors are melting the plastic resin, forming the plastic, and forcing compressed air into parison. The different types of blow molding are extrusion, injection, and stretch.
Using the extrusion process, the plastic resin is fed into a hopper and pushed along by a corkscrew type device that heats the resin as it pushes it along to the blow pin. Once the plastic material leaves the extruder, it is formed into a parison.
The heated parison enters the mold where it will be injected by compressed air into the mold where it will take the shape of the mold as the pressure of the air forces it to the sides of the mold.
The injection process does not involve the use of the corkscrew device but creates the parison in an injection mold from which it is sent to the blow mold as can be seen in the diagram below. Once the parison is in the blow mold, much like the extrusion process, compressed air is forced into it to make it conform to the shape of the mold.
The stretch blow molding process is not commonly used for the manufacturing of plastic tanks and does not involve the use of a parison. In this process, a preform is heated and then stretched using compressed air to fit the shape of the mold.
Plastic Welding -
There are three steps to plastic welding, which are somewhat similar to welding metals. The welding of plastic is much easier than the welding of other materials since plastic is pliable, softens easily, and can form a secure air tight bond. The steps to the plastic welding process involves surface preparation, the application of heat with pressure, and a period of cooling.
There are several forms of plastic welding that use different varieties of heat. The process of plastic welding is an economical way to keep a plastic tank in good repair and useful. One of the rules for welding plastics is that you can only weld like materials. When making the decision to weld, it is important to identify the type of plastic.
The next step in the process, after preparing the surface, is to make a “V” groove along the weld line. Once the “V” groove is cut, the tacking can be completed wherever the welding rod will be placed. After these operations are completed, the welding can be done.
Though there are other methods for joining plastics such as adhesives and fasteners, those types of operations do not form the same type of bond that can be made with plastic welding. The main benefit of plastic welding is a tighter and more secure seal that will last longer and be more durable. Once the process is completed, the finished seal is unnoticeable and matches with the existing material.
Chapter 3: Types of Plastic Tanks
There is an endless number of plastic tanks and designs, which are increasing as engineers find more uses for plastic tanks. The designs of plastic tanks vary according to their use with some being adaptable to any conditions while others are manufactured for a specific application.
Types of Plastic Tanks
One of the variations in plastic tanks is the type of materials used to produce them, which can be any of several varieties of polymers. Though the material is one method of classifying plastic tanks, another method is how the tank will be used with some being produced for chemical and fuel applications, which are different from those produced to store grains and solids.
One method for classifying plastic tanks is according to how they are positioned. A tank’s placement gives an indication as to how it will be used.
Vertical Plastic Tanks –
Vertical placement is the most common form of tank since they can be used for general purposes and are more flexible as well as easier to access. They are limited to above ground applications due to the thickness of their walls though they can be placed in an underground chamber made of concrete or brick.
Horizontal Plastic Tanks –
The horizontal design of plastic tanks is used for transportation applications as a mobile storage device and has the adaptability of being permanently placed or loaded on the back of a truck or trailer. The design of horizontal tanks makes them easily accessible for filling and loading purposes. They have a low profile to prevent them from disrupting the center of gravity of a vehicle.
Underground Plastic Tanks –
The basic difference between above ground tanks and underground tanks is the special engineering required to produce underground tanks since they have to be sturdier and longer lasting as well as be able to withstand the weight and force of the tons of soil on them. The purpose of burying tanks is to keep them from view, allow for extra space, and protection from vandals as well as meeting environmental conditions. Producers of underground tanks stipulate the set of guidelines for tank installation, which should be meticulously followed.
Silo Tanks –
Silo or conical tanks have to have specialized tank stands such that the contents can be accessed from their cone shaped nose at the bottom of the tank. The contents are loaded from a lid at the top of the tank and accessed through an opening at the bottom of the cone.
Double Wall Plastic Tanks –
The double wall design of plastic tanks is a tank within a tank providing secondary containment for the contents. The design of double wall tanks was created as a safety measure and a method for meeting environmental protection standards against hazardous chemical spills. Double wall tanks can have a dome that protects against rainwater seeping in between the inner and outer wall. Double wall tanks are made from high density polyethylene or cross link polyethylene, each of which offers a different form of chemical resistance.
Cylindrical Plastic Tanks –
Cylindrical plastic storage tanks are made from polyethylene or polypropylene and are resistant to rust, corrosion, UV rays, and certain types of chemicals. The strength and stability of cylindrical tanks makes them ideal for use in the pharmaceutical industry, mixing plants, and liquid storage facilities. They are produced in double and single wall construction and can be vertical free standing with a flat bottom for indoor and outdoor use or horizontal with leg supports.
Chapter 4: Plastics Used to Make Plastic Tanks
The construction of a plastic tank is based on the type of material that it will store. Plastic tanks have recently grown in popularity because of their low cost and flexibility. The industries that use plastic tanks are food processing, wastewater management, chemical manufacturing, and agriculture, to name a few.
Plastic tanks are classified, aside from their positioning, according to the type of polymer used in their manufacturing. Three of the common polymers are polyethylene, polypropylene, and fiberglass.
Plastics Used to Product Plastic Tanks
Polyethylene Plastic Tanks –
Polyethylene is a high quality thermoplastic that is resistant to weathering, abrasion, and chemicals. The durability of the polyethylene makes it an excellent solution for the production of plastic tanks. The natural color of polyethylene varies between white to yellow depending on the wall thickness of the tank. Polyethylene tanks for outdoor use have an ultraviolet light stabilizer added as an extra layer of protection.
Two forms of polyethylene are linear and cross-linked.
- Linear Polyethylene: Linear Polyethylene comes in low, medium, and high density forms. The majority of polyethylene tanks are made from linear medium density polyethylene (LMDPE) or high density (LHDPE), which have superior mechanical properties, exceptional strength, and resistance to hazardous environmental conditions. Products produced from LMDPE and LHDPE have been approved for food and medical use according to FDA regulations.
- Cross-Linked Polyethylene: Cross-linked polyethylene is a high density polyethylene that is produced by adding a catalyst to the thermoplastic resin to turn it into a thermoset. The added catalyst gives the cross-linked polyethylene its name since the addition of the catalyst links the molecules. The resulting plastic is resistant to impact, has increased tensile strength, and is fracture resistant.
Polypropylene Plastic Tanks –
Polypropylene is another form of thermoplastic made from a combination of propylene monomers. It has low density, which makes it lighter than other plastic materials. To increase its strength, it is copolymerized with other polymers such as polyethylene. The qualities of polypropylene that make it ideal for use as a storage tank is its resistance to chemicals, elasticity and toughness, and fatigue resistance.
The wide use of polypropylene is attributed to its ability to adapt to different fabrication processes. It has two main types, which are homopolymer and copolymer with the homopolymer version having the most general use. The block version of the copolymer polypropylene is the strongest variety and is impact resistant.
Polypropylene is used to store reactive elements since it has a high resistance to chemicals and corrosive materials as well as being rigid and strong. It has a high operating temperature limit of 212° F, which makes it autoclavable. A common characteristic of polypropylene is its rough, irregular interior surface.
Fiberglass Plastic Tanks –
Fiberglass storage tanks are used for underground and above ground applications since they are durable, corrosion resistant, and do not deteriorate or weather. Tanks made from fiberglass do not need waterproofing due to its impermeability and mono hull characteristics. Fiberglass is lighter than other forms of tank materials, which makes fiberglass tanks easier to relocate, install, and transport.
Chapter 5: How Plastic Storage Tanks are Used
Plastic tanks made from polyethylene and polypropylene have become a more affordable option for the storage of a wide variety of materials. Prior to the development of plastic tanks, the most common method for storing liquids, grains, and granular materials was some variety of metal containers. The advancements in plastics have created storage methods that have greater durability and strength than traditional practices.
How Plastic Storage Tanks are Used
The initial use for plastic storage tanks was as a means of storing water for livestock, crops, and irrigation. As polymers became more practical, the plastic water tank has been applied to other purposes.
Water Storage Plastic Tanks –
Plastic tanks have been a popular means of storing water since they can be conveniently connected to downspouts as rainwater harvesters or a means of collecting water for commercial and industrial use. They are essential in rural areas to help supplement the limited water supply. The flexibility of plastic tanks allows for the storage of all forms of water such as saltwater, distilled, waste, ground, rain, and melted snow water.
Chemical Storage Plastic Tanks –
Plastic storage tanks come in sizes, gauges, strengths, and specifications required for safe storage of chemicals. Since they are capable of being placed in any location and are able to endure harsh weather conditions, they have become a popular choice for industrial and manufacturing use. Polyethylene plastic tanks have gradually been replacing metal storage tanks as a safer method for storing chemicals since they do not rust, corrode, or deteriorate from wear. They are capable of storing fertilizers, pesticides, pharmaceutical products, and various forms of acids such as hydrochloric, sulfuric, sodium hypochlorite, and nitric acid. The only precaution regarding the storage of acids is the type of plastic used to make the tank. To determine which type tank can be used, an examination of the strength and resistive properties of the plastic has to be assessed.
Fuel Storage Plastic Tanks –
Plastic storage tanks have been found to be an ideal means for the storage of fuel and are used by racetracks, factories, and repair garages. The polyethylene core of plastic storage tanks is capable of storing any type of fuel from diesel and gasoline to butane and natural gas.
Grain Storage Plastic Tanks –
Grain feed bins are used to store corn, soybeans, and granular products. They are made of UV treated polyethylene that can be 3/16 of an inch thick. The main reason for using plastic storage tanks for grains is their resistance to rust, corrosion, and weather, which has been a problem with metal storage units. The smooth interior surface of plastic tanks reduces bridging or the need for rivets and clogging seams.
Plastic Septic Tank –
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 concerns for septic tanks is their reaction to chemicals in the soil or gases from a sewage system. The polyethylene used to produce plastic septic tanks is resistant to the soil chemicals and sewage system gases.
Chapter 6: Industries that Use Plastic Tanks
Plastic tanks have become an essential part of several industries due their durability and ability to withstand harsh and hazardous conditions. As the applications for plastics has improved and broadened, more commercial, governmental, and manufacturing operations have found uses for plastic tanks as a valuable and economical asset.
Industries that Use Plastic Tanks
The groups and organizations that use plastic tanks include fire departments, sewage operations, pharmaceutical companies, electroplating manufacturers, and water treatment facilities, to name a few.
Fire Department Plastic Tanks –
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.
Electroplating Plastic Tanks –
Due to the nature of the electroplating process, plastic tanks for plating must have excellent chemical resistance since strong acids, organic solvents, degreasing agents, and electrolytes are part of the plating operation. Electroplating plastic tanks are built for their specific function and designed to withstand the demands of the electroplating industry. They have racks, bus bars, and other added features.
Pharmaceutical Plastic Tanks –
Plastic tanks for the pharmaceutical industry have to adhere to a strict set of standards as outlined by the American Society for Testing and Materials (ASTM) as well as the requirements of governmental and other regulatory agencies. The main concern for pharmaceutical tanks and equipment is sterilization and cleanliness. It is for these last two reasons that plastic tanks are so widely used in the pharmaceutical industry. Pharmaceutical plastic tanks are used to store and transport powders, chemicals, and granular materials.
Sewer Truck Plastic Tanks –
Sewer truck plastic tanks are used in place of metal tanks because they are rust and corrosion resistant, which gives them a longer life and less maintenance. Plastic is much easier to clean and sanitize as well as being resistant to the chemical effects of wastewater. Their lighter weight and large capacity make them ideal for cutting down on truck trips and refuse removal.
Degreasing Plastic Tanks –
Degreasing plastic tanks are made from long lasting polypropylene. They are ideal for the degreasing operation due to their non-sticky corrosion free surface. The ease of mobility for plastic degreasing tanks makes them flexible enough to be used in a variety of locations or be stored when not in use. Unlike metal tanks, plastic degreasing tanks are one solid piece and leak proof.
Food Processing Plastic Tanks –
For a plastic tank to be used for food processing, it has to meet the requirements of the Food and Drug Administration (FDA) regarding equipment used for the production and handling of food products. Plastic tanks for food processing are approved as finished products and not according to the materials that are used to produce them. Though a resin may meet the required standards, that does not mean that the tank produced from the resin has the same qualifications.
The biggest challenge for plastic food tanks is drainage since any product that is left as residue in a tank may spoil or rot. It is essential that a plastic food storage tank be able to be completely drained of all products to avoid hazardous spoilage. Further considerations are any fittings or access points. If such additions are not properly secured and sealed, they may cause leaks and waste.
Fish Farming Plastic Tanks –
The types of tanks used for fish farming have to meet the same standards as those for the handling of any other food product as set by the FDA. Plastic tanks for fish farming are constructed with an overflow system to help maintain a consistent water level. They include dividers that allow fish to move from one tank to another as they grow. For ease of transfer, fish farming tanks include drop in baskets and chute systems for further assistance in transferring fish.
A major requirement for fish farming tanks is the inclusion of pumping and filtration systems to ensure the health and safety of the fish. These are further stipulations as outlined by the FDA.
Agricultural Plastic Tanks –
Agriculture makes the greatest use of plastic tanks because they are flexible, durable, strong, long lasting, and able to withstand harsh weather. The two main functions of agricultural plastic tanks are for storage and transporting of liquids such as fuels, fertilizers, and pesticides. The main reason that plastic tanks are so widely used in agriculture is because they are safe, worry free, and secure. Farming demands strong tools that can last but be light enough to be easily manipulated. Plastic tanks are able to meet all of those demands.
Chapter 7: How to Care for a Plastic Tank
As with any tool, plastic tanks require proper care in order to perform. Though plastic tanks are very sturdy and long lasting, they can deteriorate if not inspected and maintained. This is especially true for tanks that are in hostile or hazardous environments. Tanks designed to store volatile or explosive materials require special attention for safety and protection of the environment.
How to Care for a Plastic Tank
One of the greatest dangers to any type of sensitive equipment is elevated temperatures since heat can age and deteriorate equipment. In the case of plastic tanks, prolonged use of a tank at high temperatures can drastically shorten its usefulness. The effects of temperature depend on the content of the tank, its size and configuration, how it was constructed, the thickness of its walls, and the type of supports it may have.
Determining the effects of heat on buried tanks is obviously more difficult though most buried tanks have sufficient insulation and are specially designed for their function and environment.
Ultraviolet Light –
When thermoplastics have not been treated with a UV protective coating, they absorb the rays of light, which causes discoloration and makes them brittle. If the exposure continues, the thermoplastic will crack. Under conditions where there are elevated temperatures, the cracking is accelerated. One of the specifications that manufacturers examine when constructing a plastic tank is the types of weathering and harsh conditions the tank may be exposed to. They take extreme precautions to ensure that their tanks meet the needs of the applications.
All polyethylene materials, depending on the type, are subject to some form of cracking. This is especially true when they are exposed to certain detergents. While many plastics crack under stress, certain varieties are resistant to such effects. Stress cracking is caused by surface agents such as fillings, bands, and tie downs. Various safety procedures and proper care can avoid any harm caused by cracking.
One of the first considerations for the health and care of a plastic tank is its placement. If they are positioned on uneven ground or locations of high traffic, they can be susceptible to stress and cracking. It is essential that plastic tanks be checked to ensure that they have proper support whether they are used for transport or in place storage. Special care should be taken during loading and unloading processes such that the tank is not out of balance and is centered. The proper positioning of the bottom of the tank can prevent any harm or damage.
A difficult part of installing a plastic tank is determining the effects of the surrounding conditions. The problem with this aspect of the process is being able to predict any forms of future disturbances. Plastic tanks have to be positioned so that they will not be subjected to damage from falling debris. This requires considering the place of trees, overhangs, and other natural obstacles. During severe weather conditions, the tank may be designed to endure any temperature changes or precipitation. What it may not be able to withstand is having things fall on it such as trees or rocks.
Tank Specifications –
Not all plastic tanks are created equal. Though there are generic tanks that can be adapted to a variety of conditions, many tanks are designed for a singular purpose. When purchasing, using, and installing a tank, it is important to study the manufacturer’s specifications and restrictions since some tanks have temperature and environmental requirements. In most cases, special purpose tanks have been manufactured for their function and have been purchased for that purpose. Knowing the tank's limitations can help in lengthening its lifespan.
A key to the usefulness of a tank is keeping it clean. This may seem to be a trivial consideration since a tank is a tool designed for heavy duty work. As with any tool, maintenance is key to how long it will last. In the food and chemical industries, the cleaning of tanks is a planned and regular requirement that is added to the workday. This may not be true for tanks used for other purposes and should be given close consideration.
Reverse Osmosis Filter Systems –
Plastic tanks used for the reverse osmosis process are specially designed to withstand the high pressure of the process. The pressure of the system is the main reason that tanks for reverse osmosis should be regularly maintained and carefully checked. Though most plastics are capable of enduring high pressure conditions, it is always a good practice to examine the condition of the tank for cracks, weak points, or deterioration.
Chapter 8: Plastic Tank Regulations
Since plastic tanks store volatile materials, food products, acids, and chemicals, the Environmental Protection Agency (EPA) first developed regulations for storage tanks in 1988, which mainly focused on various forms of metals, at the time. A few years ago, the agency updated their regulations with more specific requirements.
A major concern for the EPA is underground tanks since they are mainly used to store fuel and collect waste. Seepage from underground tanks can be an extreme environmental hazard. The significance of underground tanks and their potential impact on the environment prompted the EPA to establish a new set of regulations designed to address the underground tank issue.
Tanks for the production of food and pharmaceuticals have regulations established by the Food and Drug Administration (FDA), which regulates the types of materials used in the production of food processing tanks and the design of tanks.
Environmental Protection Agency (EPA) –
Regulations for plastic storage tanks by the EPA fall into two classifications, which are underground storage tanks (UST) and above ground storage tanks (AST). Regulations covering these types of tanks are covered under Spill Prevention, Control, and Countermeasure (SPCC) regulations or 40 CFR Part 112.
The SPCC defines a bulk storage container as:
… any container used to store oil. These containers are used for purposes
including, but not limited to, the storage of oil prior to use, while being used,
or prior to further distribution in commerce. Oil-filled electrical, operating, or
manufacturing equipment is not a bulk storage container. (from epa.gov/ust)
To assist in the inspection of bulk containers, the SPCC supplies a fact inspection sheet that can be accessed on the EPA website. The main concern of the regulations is directed at the storage of volatile materials such as fuels, gases, and chemicals.
Food and Drug Administration –
The FDA is interested in any materials or equipment that will come in contact with food or items for human consumption. In the case of plastic tanks, it has a list of approved resins that can be used for plastic tanks that will be used for food storage or plastic tank construction. Manufacturers that produce food grade plastic tanks adhere stringently to the stipulations as outlined by the FDA, which increases the appeal of their products.
- A plastic tank is a large capacity liquid or granular storage unit that can be vertical, horizontal, below ground, or movable.
- There are a wide variety of methods used to produce plastic tanks with polyethylene and polypropylene being the most common raw materials.
- There is an endless number of plastic tanks and designs, which are increasing as engineers find more uses for them.
- Plastic tanks have recently grown in popularity because of their low cost and flexibility.
- The advancements in plastics have created storage methods that have greater durability and strength than traditional practices.