Plastic Tubing

Chapter One – What is Plastic Tubing?

Plastic tubing is a form of tubing that is manufactured from a mixture of a polymer with a variety of chemicals to form a material that can be solid or flexible. Since its first use in the 1950’s, plastic tubing has revolutionized industrial processes and has found a use in a wide variety of applications.

The popularity of plastic tubing is due to its adaptability and flexibility. It is produced in a wide variety of wall thickness, diameter, tolerance, and strength using a combination of materials to specifically fit a variety of applications.

Chapter Two – Applications for Plastic Tubing

The flexibility, durability, and adaptability of plastic tubing makes it applicable for industrial applications that require long wear and endurance as well as commercial use in consumer products and homes. The main benefit of plastic over steel, aluminum, or other materials is its consistent strength and cost effectiveness since it is far less expensive to produce.

Applications for Plastic Tubing

Pneumatic

Pneumatic tubing is flexible and capable of handling the compression of a pneumatic system. It is ideal for outdoor applications since it can endure temperatures ranging from -4o F to 140o F, which makes it useful in any environment or situation. In general normal use, plastic pneumatic tubing can withstand 115 PSI at 68o F.

Mailing

Clear plastic mailing tubes are used as a method for delivering literature, samples, and promotional materials. They have heavy thick walls designed to endure the rugged handling of the mail service and come in a wide variety of lengths and diameters.

Banking

Banking makes use of plastic tubing in two ways. The long tubes that reach from the teller to the customer are made of thick walled sturdy plastic. The carriers that carry the customer’s transaction through the tubes are also made of sturdy thick walled plastic.

Farming

Plastic tubing for farming is used for water systems since they are simple to install, durable, last a long time, and do not corrode or rust. The quality that makes them the most useful for farming is that they can run for hundreds of feet without the need for joints or connectors.

Liquid

There are several types of plastic tubing used to move liquids. In the case of drinking beverages, plastic tubing must be Food and Drug Administration (FDA) grade and meet the standards for pressure, temperature, and cleanliness. Liquid plastic tubing is made from polyurethane, polyethylene, nylon, or PVC.

Automotive

Plastic is a major part of the construction of automotive parts. Plastic tubing is used for fuel lines and fuel fillers for its flexibility and endurance.

Marine

As with automobiles, many of the parts on marine equipment include plastic parts. One of the components on a boat is its bilge pump tubing, which can be made of PVC for its abrasion resistance and flexibility. The heavy duty qualities of PVC tubing makes it chemical and oil resistant.

Medicine

Medical tubing is used to deliver fluids to and from the body and is made from small complex custom plastic extrusions. It has to be produced in an isolated environment away from any possibility of contamination. Medical grade tubing is manufactured with single, dual, or triple lumens and cut to lengths or made into reels.

Peristaltic Pump

Peristaltic or roller pumps are designed to move liquids through flexible plastic tubing. A rotor with wipers attached to its circumference turns and squeezes the tubing, which moves the liquid, as seen in the image below.

Chapter Three – How Plastic Tubing is Made

The two methods for the manufacture of plastic tubing are extrusion and pultrusion. The difference between the two methods is how the molten plastic moves through the die. With extrusion, the molten plastic is pushed through the die, while with pultrusion, it is pulled through.

Plastic Tubing Manufacturing

Extrusion

There are several steps to the extrusion process. The main ingredient is a polymer resin, which is referred to as nurdles, pellets, granules, flakes, or powder, that are fed into a hopper mounted on the extruder’s barrel. The resin descends the feed throat of the hopper into the barrel that has a screw that moves the resin toward the die. During its movement down the barrel, pushed along by the screw, the resin is slowly heated to a melting temperature. Extrusion uses highly technical equipment to control the temperature, speed, force, tension, and time of the process.

Flexible and rigid tubing is formed using the extrusion process. In coextrusion, two or more materials can be combined to form tubing with a rigid core and flexible exterior.

The video below, from Freelin-Wade Co., gives a step by step explanation of the extrusion process.

As explained in the video, modern extrusion is monitored by computerized equipment to ensure the final cross section perfectly matches the engineered profile.

Pultrusion

Pultrusion, like extrusion, is a continuous feed process used to produce a tubing profile. Unlike extrusion, pultrusion pulls reinforced fibers that have been wetted in a thermoplastic resin through a die. Polymerization happens as the fibers go through the die.

The video below, from Bedford Reinforced Plastics, Inc., offers a general overview of the pultrusion process.

Pultrusion is a low maintenance and efficient method for producing plastic tubing that is corrosion resistant as well as having low thermal conductivity.

Plastic Tubing Materials

Acrylic Tubing:

Acrylic tubing is clear, impact and UV resistant, and half the weight of glass. It is used in a wide variety of applications from lighting to various industrial processes.

PVC Tubing (poly vinyl chloride):

PVC tubing is chemical, corrosion, abrasion, and wear resistant with excellent flexibility. It is used in several industrial applications.

CPVC Tubing (Chlorinated Polyvinyl Chloride):

The main difference between CPVC and PVC is CPVC’s higher corrosion resistance at higher temperatures.

Fiberglass Tubing:

Fiberglass plastic tubing is pultruded and is a combination of fiberglass and thermoset polyester or vinyl. It comes in hundreds of shapes and is corrosion and UV ray resistant. Fiberglass tubing is used as an electrical insulator and has dimensional stability.

Nylon Tubing:

Nylon tubing is lightweight and corrosion and abrasion resistance, which makes it useful for a variety of industrial applications. It has excellent elastic memory that makes it capable of being flexed multiple times over long periods without exhibiting fatigue or fracturing. Nylon tubing is impact resistant, even at below freezing temperatures and has very low moisture absorption.

Polycarbonate Tubing:

Polycarbonate tubing is capable of withstanding harsh environments. It is lightweight but flame and impact resistant as well as strong and lightweight.. Polycarbonate tubing can be machined and drilled without cracking.

Polyethylene Tubing:

Polyethylene tubing has a waxy, tough texture and is used for its resistance to erosion by water and chemicals. It has a very high resistance to cracking under stressful environmental conditions.

Polystyrene Tubing:

Polystyrene tubing is lightweight, flexible, and durable, which makes it useful for safely transporting fluids and gases. It has excellent vapor and moisture resistance and comes in burst prevention rates to meet heat resistance standards.

Silicone Tubing:

The brief video below, from NewAge Industries, explains the benefits and qualities of silicone tubing.

Vinyl Tubing:

The most common form of vinyl tubing is PVC, which is polyvinyl chloride. Vinyl tubing is resistant to chemicals, lightweight, has exceptional strength, non-toxic, and transparent with a high melting point.

Polypropylene Tubing:

Polypropylene tubing is very similar to polyethylene but is more rigid, has a higher melting point, can be made optically clear, and is puncture and chemical resistant. It can be used in environments with temperatures that range from freezing to 275o F.

HDPE Tubing (High Density Polyethylene):

High-density polyethylene tubing has an exceptional strength to density ratio with a low risk of shattering, corrosion, and other malfunctions or failures. It is used for transfer of water, air, and chemicals. HDPE can be sterilized by boiling and withstand high pressure as well as being abrasion resistant.

PTFE Tubing (Polytetrafluoroethylene):

PTFE tubes are flexible and able to withstand temperatures that range between -390°F to 500°F, as well as being resistant to corrosive liquids and gases. One of its main features is that it will not crack when in high temperature environments. It is commonly found in laboratories and chemical operations.

EVA Tubing (Ethyl Vinyl Acetate):

EVA tubing is flexible, impact resistant, able to withstand very low temperatures, and resistant to grease, oil, and UV rays. It is used in hospitals, surgical situations, and the pharmaceutical industry. The temperature range for EVA tubing is between -76o F and 140o F and meets FDA standards.

Polyurethane Tubing (PU):

Polyurethane tubing is resistant to abrasion but is flexible kink resistant with excellent memory qualities. It easily stretches and flexes but returns to its original shape. PU tubing is used in high pressure and medical applications or where flexibility is important. Its resistance to gasoline, oils, and other petrochemicals has made it a choice for fuel lines or other similar applications.

Chapter Four – Plastic Tubing Design

With the wide variety of materials and applications for plastic tubing, producing a tubing to fit a specific application requires a close examination of the qualities required. Since plastic is such a resilient material, it is easy to decide to use it as a component. The difficulty arises when deciding what will be the necessary features.

Plastic Tubing Design

Strength

Measuring the mechanical properties of a material, and its tensile strength, is the first determination for choosing a material. Tensile strength is the amount of stress plastic can endure before breaking. The tensile strength of plastic varies between 12,400 psi up to over 20,000 psi. The chart below has a list of a wide variety of plastics and their megapascal tensile strength at 23o C or 73o F.

Diameters

Tubing is measured by the inside diameter (ID) and outside diameter (OD), which can vary between 0.125” to 4”. The measurement between the ID and OD is the wall, a means for determining the strength of the tubing.

Wall Thickness

The wall thickness is determined by subtracting the ID from the OD (OD) and dividing the answer by two.

Flexibility

The flexibility of plastic tubing is determined by the material used to manufacture it. PVC and polyurethane are the most flexible.

Fittings

There are a variety of fittings for plastic tubing that include compression, push to connect, quick turn, threaded, barbed, socket, and flanged. The determination of the type of fitting is in accordance with how the tubing will be used.

Color

There is a limitless number of colors used to make plastic tubing, which also include translucent and clear.

Length

Plastic tubing can be made to any length, depending on the needs of the application. It can be a few inches up to hundreds of feet.

Cost

When examining the cost of plastic tubing and comparing it to steel or stainless steel for tensile strength, steel and stainless steel are far stronger. The biggest difference between plastic and steel is cost. For the cost of producing a half dozen stainless steel tubes, hundreds of flexible plastic tubes can be made.

Durability

The durability and strength of plastic depends on wall thickness and resin blend. The strength of plastic tubing is proportional to the amount of stress it will endure. Plastic can take a great deal of abuse before it gives out.

Corrosion

All plastic is corrosion resistant. The type of polymer used determines the amount of corrosion resistance. The types of corrosion resistant plastics are polyolefins and PVC. Polyolefins are polyethylene and polypropylene, which come in various densities and molecular structures for ease of design.

Microbial Properties

The resin for plastic tubing can be manufactured with antimicrobial properties included in the pellets. The microbial properties of plastic tubing are required for food storage, coolers, water tubes, and medical tubing. The antimicrobial additives prevents contamination and keeps the tubing sanitized.

Toxicity

Plastic products have the potential for being toxic. The amount of toxicity depends on the type of plastic resin used in the manufacturing process. When making the decision to produce plastic tubing, consideration is given to the toxic nature of the materials and is part of the design process.

Chapter Five – Characteristics of Plastic Tubing

The characteristics of plastic tubing vary depending on the materials, configuration, and production methods used in its manufacturing. Surgical and industrial tubing widely vary in their application. Though there may be radical differences between functions, all plastic tubing has certain common features.

Characteristics of Plastic Tubing

Hollow Shafts

Plastic tubing is a hollow shaft of plastic designed to transport gas, fluids, or some form of solid, flaky material. Though circular is the most common form of a plastic tubing profile, it comes in a variety of other shapes, as pictured below.

Polymer

As the name implies, all plastic tubing is made of one of the many forms of plastic, which begins with a polymer. It is chosen as the base material for its strength, endurance, corrosion and rust resistance, and cost.

Versatility

The strength, endurance, and transparency of plastic tubing varies according to the materials used to produce it. Regardless of those distinctions, it is one of the most used components in manufacturing due to its low cost and versatility.

Clear

Plastic tubing can be produced with the same clarity as glass but not as fragile or breakable with greater strength and endurance.

Functionality

Plastic tubing can be manufactured to withstand any conditions or materials. Unlike other tubing types, plastic tubing does not have to be specially treated to move chemicals or corrosive substances.

Durability

Though plastic does not have the tensile strength of steel or stainless steel, it is more capable of withstanding the strain of daily wear. It is able to take significant harm and damage and still maintain its strength.

Recyclable

All plastics can be reprocessed and reused for the manufacturing of other products. Once plastic tubing has reached the end of its usefulness, it can be sent back to the manufacturer to be processed into pellets or resin and sent through extrusion a second time.

Chapter Six – Types of Plastic Tubing

The number of materials used to manufacture plastic tubing is matched by the number of types of plastic tubing, which ranges from highly sanitary tubes used in cleanrooms and surgery to drainage tubes for sewage and waste removal. Plastic tubing is engineered and designed to fit specific applications and can be formed, shaped, and configured for any number of conditions.

Types of Plastic Tubing

Corrugated Plastic Tubing

Corrugated tubing is used for chemical processing, in corrosive environments, laboratories, and high purity fluid and solvent transfer. It is very flexible and can be extended or compressed without affecting the ID. Corrugated plastic tubing can be produced in any length in a variety of ID’s.

Heat Shrinkable Plastic Tubing

Heat shrinkable tubing is used as insulation for wiring. It is placed around the wire and then shrunk to fit snuggly. It is resistant to fuels, lubricants, acids, and solvents at high temperatures.

Medical Plastic Tubing

Medical plastic tubing is manufactured to the exacting standards of the United States Pharmacopeia organization (USP) and the National Sanitation Foundation (NSF). USP Class VI defines the requirements for biological reactivity, while NSF 51 outlines the use of plastics with food products. Medical tubing has to be translucent, able to be sterilized and reusable, and nonreactive with bodily fluids or tissues.

Square Plastic Tubing

Square plastic tubing has limited use and is sometimes used for its appearance. It has the same functions as cylindrical tubing and is able to transport liquids and gases. Due to its strength, it is included in the production of lawn furniture.

Hard Plastic Tubing

Hard or rigid plastic tubing is made from all of the different types of fabricating materials. It is used as a conduit or construction material and has multiple industrial applications.

Small Diameter Plastic Tubing

Small diameter tubing, also known as miniature tubing, is used in applications that need regular tubing but of a smaller size. It is made from polycarbonate, polypropylene, polyethylene, polystyrene, and PVC to name a few. It is used in electrical components, swab sticks, medical products, and dispensing tubes in various lengths.

Centrifuge Plastic Tubing

Centrifuge plastic tubing is cylindrically shaped tubes that are placed in centrifuge slots to analyze and separate tested materials. They are high strength, precision containers that can safely hold a wide variety of materials. Plastic centrifugal tubes are more commonly used due to their cost effectiveness.

Chapter Seven – Plastic Tubing Regulations and Specifications

The regulations for the production of plastic tubing mainly pertains to its use in the food industry and the transport of water. Aside from governmental regulations, several other organizations monitor and develop specific guidelines for materials that come in contact with the public.

Plastic Tubing Regulations and Specifications

FDA (Food & Drug Administration)

The FDA oversees any products that come in contact with food or beverages. Since plastic tubing is a major part of the food industry, the FDA has established regulations specifying the cleanliness and sanitary standards for food processing plastic tubing. Materials used in plastic tube production are tested for composition, additives, and properties. If it meets the requirements, it is classified as FDA compliant. FDA CFR 21 is an all-encompassing regulation that includes requirements for materials used for medical purposes.

USDA (U.S. Department of Agriculture)

The USDA regulates equipment used in the production of meat and poultry products. The Food Safety and Inspection Service (FSIS), a department of the USDA, provides guidelines regarding several aspects of food production following FDA requirements listed in CFR 9.

3A-Dairy

The 3A-Dairy group is a voluntary organization that has the goal of improving the quality, standards, and equipment used in the production of dairy products. Its main focus is enhancing the sanitary conditions involved in production. The organization works with food handling manufacturers that are interested in improving their methods and gives a 3-A Sanitary Standards, Inc. compliance seal to those who meet their requirements.

NSF (National Sanitation Foundation)

The NSF was founded to standardize sanitation and food safety requirements. It has over 80 requirements for public health and safety. It covers all sectors of food production. One of its critical areas for examination and testing is all equipment that comes in contact with drinking water such as plumbing, water treatment chemicals, and water filters.

NSF Standards that relate to Plastic Tubing are:
• 51 Plastics in Food Equipment
• 61 Drinking Water System
• 14 Manufacture of Fittings

USP (United States Pharmacopoeia)

The USP is a public standards authority for medicines and health care items. It sets standards for quality, purity, strength, and consistency. USP Class VI standards determine the toxicity of materials and their dangers to people. Any tubes that come in contact with body tissue or muscles are tested and graded. The USP uses a variety of tests to determine if a material meets their standards.

Conclusion

• Plastic tubing is a form of tubing that is manufactured from a mixture of a polymer with a variety of chemicals to form a material that can be solid or flexible.
• Plastic tubing is produced in any wall thickness, diameter, tolerance, and strength using a combination of materials to specifically fit various applications.
• The main benefit of plastic tubing over steel, aluminum, or other materials is its consistent strength and cost effectiveness since it is far less expensive to produce.
• The two methods for the manufacture of plastic tubing are extrusion and pultrusion.
• The number of materials used to manufacture plastic tubing is matched by the number of types of plastic tubing, which ranges from highly sanitary tubes used in cleanrooms and surgery to drainage tubes for sewage and waste removal.