Plastic Tanks

Plastics work well as tank materials because they are typically less likely to react to any liquid that may be stored inside the tank, which is particularly relevant for the storage and processing of aggressive chemicals such as acids and caustics for industrial chemical applications. Additional industries and applications that benefit from the utilization of plastic tanks versus metallic tanks, such as stainless steel tanks, include: agriculture, for use in irrigation and fertilization systems for food production applications; petrochemical, for the storage and transport of oil and gas; industrial, used in applications such as electroplating, recycling, parts washing and more; and wastewater, in order to be used in municipal waste water treatment plants and other water treatment facilities.

There are many different methods of categorization when it comes to plastic tanks. However, the three main ways are: by the material being contained, the type of material the tank is fabricated from and the application/design of the tank. Some common types of plastic tanks that fall into the first category of defined per the material being contained are water tanks, plastic fuel tanks, plastic oil tanks and chemical tanks. Water tanks can be fabricated from a wide variety of plastic materials, but the most often used material is polyethylene (PE) although polypropylene (PP), polyvinyl chloride (PVC), and polyvinylidene fluoride (PVDF) are viable options as well. PE is so commonly used as a material for water tanks because it is a light, chemical-resistant thermoplastic. Plastic fuel tanks are used for many applications including providing safe storage and transportation of flammable substances, and for gauging substance levels in the engine and anticipating the potential for harm. Often, they are typically fabricated from five different materials: high density polyethylene (HDPE), polypropylene (PP), regrind plastic (recycled polyethylene), a plastic adhesive or ethyl vinyl alcohol (EVOH). Plastic oil tanks are much the same as plastic fuel tanks, but are more commonly fabricated from materials such as FRP (fiberglass reinforced plastic) and molded polyethylene. Lastly, chemical tanks include a wide range of plastic tanks that are used in the storage of mild to aggressive chemicals.

In terms of plastic tanks that are categorized by the type of plastic materials that are used to fabricate them, there is such a wide range of materials that this category is by far the largest of the three. However, the most common types include polypropylene tanks, polyethylene tanks and FRP tanks. Polypropylene is an oft-used plastic material that features advantageous characteristics such as a lightweight structure, high resistance to moisture and heat, low density and melting point of 320º F. Polypropylene is much stronger than polyethylene, and is a low-cost material. However, polyethylene is still an even more popular plastic material; polyethylene tanks include tanks fabricated from high-density polyethylene (HDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), linear low density polyethylene (LLDPE) and cross-linked polyethylene (XLPE). Much of polyethylene's popularity as a plastic tank material is due to its structural variability and its beneficial characteristics including high-resistance to water, acids, alkalis, solvents and chemical corrosion. Lastly, FRP tanks are fabricated from fiberglass reinforced plastic (FRP) which can also be referred to as glass reinforced plastic (GRP). FRP tanks are often used in applications involving food processing because it is a Food and Drug Administration (FDA) approved material.

Lastly, there is also a very large group of plastic tanks that are categorized by there application/design. For industrial application, some examples of the more common types of these include cone bottom tanks, double wall tanks, storage tanks and septic tanks. Categorized by design, cone bottom tanks and double wall tanks are designed in a specific manner in order to fit the needs of the desired application. Cone bottom tanks, for instance, are designed so that distribution from the bottom of the tank is both incredibly simple and highly efficient. Double wall tanks, on the other hand, are fabricated with an extra layer of plastic material in order to reinforce the wall (now walls) of the tank, and provide additional safety in the transportation, storage and processing of aggressive materials. Categorized by application, storage tanks and septic tanks are used for specific purposes, although they can also seem very broad. For instance, storage tanks are used solely for storage applications; however, storage can be required in so many different industries, for varied materials and purposes that storage can be a very broad category of plastic tank in itself. Septic tanks are used for a much more specific purpose, as they are defined as tanks used to store substances utilized in sewage processes. Septic tanks consist of two major parts, a septic tank and a drainfield, and function as on-site sewage treatment systems.

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Plastic Tank Types

• Chemical tanks are made of plastic provide superior resistance to harsh chemicals that no other material can match.
• Clarifiers are tanks in which sediment and other precipitate settle. 
• Cone bottom tanks have a bottom that is angled to come to a point and are used when complete drainage of the materials or liquids inside is necessary.
• Double wall tanks provide superior protection against spillage of hazardous chemicals. Double wall tanks are used especially in high-pressure applications.
  
• Dual laminate tanks are tanks in which a thermoplastic lining - consisting of resins, such as polypropylene, polyvinyl chloride and polyvinylidene fluoride - is bonded to a fiberglass structure for reinforcement.
  
• FRP Tanks are manufactured from a combination of resin and glass and are rust-proof and long-lasting. FRP tanks formed from FDA-accepted raw materials are acceptable for potable (fit to drink) water. 
• Plastic fuel tanks can provide safe storage and transportation of flammable substances or they can be used to gauge the substance level, venting as well as possibly feeding the engine and anticipating the potential for harm.
• Plastic oil tanks are used to transport, store and hold oil, and are generally made of industrial grade plastics like fiberglass reinforced plastic (FRP) and molded polyethylene.
• Plastic water tanks are used as primary or secondary storage for drinking water, water reserves and fire safety. The use of plastic water tanks is increasing, as the availability of drinking water to the consumer is decreasing.
  
• Poly tanks are more durable, provide more chemical and corrosion resistance, require less maintenance and cost less than comparable steel and fiberglass tanks. Poly tanks are used in the water treatment and chemical processing industries for such hazardous fluids as sodium hypochlorite, sulfuric acid, caustic soda and hydrochloric acid. 
• Polyethylene tanks are a type of poly tank, provide atmospheric, or non-pressure, storage of a multitude of substances.
• Polypropylene (PP) tanks provide excellent chemical and corrosion resistance, have a wide operating temperature, high rigidity and good structural strength and can be easily fabricated and welded using hot air, extrusion and fusion equipment.  Polypropylene tanks are ideal for a variety of electroplating applications and are increasingly being used in the demanding environment of steel process plants.
  
• Septic tanks are on-site sewage treatment systems that store waste materials in a large plastic tank.
• Storage tanks are plastic containers used to store various substances in industrial settings.
• Water tanks are plastic storage containers designed to hold water.

Plastic Tank Terms

Additive - A substance added to a polymer to increase the effectiveness, but not the strength, of the polymer. Examples of additives include flame-retardants, anti-static compounds, pigments and lubricants.
 
Bag Molding - The process in which atmospheric force is applied to a laminate using an elastic or woven material.
 
Blister - A flaw that forms between the laminate layers or between the laminate and the gel coat film of a fiberglass tank.
 
Blow Molding (http://www.iqsdirectory.com/blow-molding/) - The formation of a hollow object, such as plastic tanks, by using air to expand a hollow tube, called a parison, against the internal walls of a mold.
 
Casting - The process in which a mold is filled with a mixture of resin, fillers and/or fibers to form the end product, such as plastic tanks.
 
Contact Molding - A process in which layers of polymer and reinforcement materials are applied to a single or open mold, producing one finished cosmetic side.
 
Copolymer - A polymer made up of two monomers in which each repeating unit in the chain consists of units of both monomers.
 
Crazing - Very thin cracks in a polymeric material caused by chemicals or other agents, such as ultraviolet radiation.

Degree of Polymerization - The length of the molecular or monomeric units in a polymer chain. The degree of polymerization determines the properties of the polymer.

Depolymerization - The breakdown of a polymer to its original monomers or to a polymer of a lower molecular weight. Depolymerization often occurs when a polymer is exposed to chemicals or certain environmental conditions, such as high temperatures.
 
Die - A piece of equipment, usually consisting of metal, through which a substance, such as plastic, is forced in order to provide shape to the substance such as the shape used in creation of plastic tanks.
 
Extrusion (http://www.iqsdirectory.com/plastic-extrusions/) - In plastic shaping, the process of softening plastic through the application of heat and pushing the plastic through a die.
 
Filler - Typically inert organic or inorganic material that is added to resins, plastics or gel coats, in order to change the properties, increase volume or decrease the cost of the end product.
 
FRP (Fiber Reinforced Plastic) - Also called GFRP (glass fiber reinforced plastic) GRP (glass reinforced plastic) or RP (reinforced plastic) it is a durable, rust-proof material that is a combination of glass and resin.
 
Gel-Coat - A surface coat of colored or clear polyester resin that cosmetically enhances fiberglass laminate and provides it with good weatherability.
 
Hand Lay Up - The process in which fiberglass and resin layers are built up manually using hand rollers, spray equipment and brushes.
 
Hot Air or Gas Welding - The process of joining two pieces of plastic by blowing heated air or gas to melt the plastic pieces.
 
Injection Molding (http://www.iqsdirectory.com/plastic-molding/) - The process of creating an object, such as a tank, by applying pressure to molten plastic in order to push the plastic into a mold. The mold is then cooled to produce the final plastic form.
 
Laminant - A composite formed by lamination, a process in which thermoset polymers and fiber reinforcement are layered.
 
Mold - A hollow, heat-resistant container in which liquid substances can be formed into solid shapes by allowing the fluid to solidify within the mold cavity.
 
Monomer - The most basic polymeric unit, usually a liquid or a gas, consisting of molecules from the same organic substance.
 
Permeability - The ability of liquids and gases to flow through a substance. Low permeability is advantageous in plastic tank resins.
 
Plastic (http://www.iqsdirectory.com/plastic-materials/) - A material whose essential ingredient is an organic substance of large molecular weight and whose end state is solid. Plastics can be shaped by flow at some stage of the manufacturing process.
 
Plasticizer - A material added to a plastic to make it more workable and flexible.
 
Polymer - Two or more monomers bonded together through a chemical reaction. Each polymer consists of a chain of repeating monomers.
 
Potable Water - Water fit for human consumption. Typically dispensed form plastic water tanks.
 
Regulated Substance - Petroleum or any hazardous substance stored in an industrial tank. Hazardous substances are defined in the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).
 
Reinforcement - Substance added to a polymer to increase the strength of the plastic. Examples include clay, mica and glass fibers.
 
Resin - A class of polymers, or plastics, chemically different to naturally occurring resins, which are sticky substances obtained from certain trees and plants. Examples of resins include polyethylene, polyurethane and acrylics.
 
Rotational Molding (http://www.iqsdirectory.com/rotational-molding/) - Also called rotomolding it is the formation of a hollow object, such as a tank, by simultaneously rotating and heating a mold filled with thermoplastic resin powder. As the mold rotates, the resin evenly coats the mold walls and is then cooled into the final form, providing seamless molding at a low manufacturing cost.
 
Stress Cracking - Cracking that occurs as a result of mechanical stress. In most cases, tiny cracks caused from exposure of the plastic to chemicals or ultraviolet radiation are already present, so that when stress is applied to the plastic, the cracks enlarge and spread, creating a greater fracture.
 
Thermoplastic - Category of plastics that have the potential to soften and reform when heated, and harden again during cooling. During the process, the physical makeup of the plastic does not change.
 
Thermoset - Category of plastics that cannot be reformed upon reheating. Thermosets remain permanently hard.
 
Underground Storage Tank System - Plastic tanks system storing a regulated substance, such as petroleum, in which at least 10% of the plastic tanks, plastic tank piping and other equipment associated with the tank is located underground.