• SkillCat Team

Pipes & Tubes - Types, Materials & Measurements

Updated: Jun 23

Piping: Chapter 1


Piping and Tubing


In this module, you will learn about:

- What piping is,

- What tubing is, and

- What different pipe and tube materials are Skip to quiz!


Piping and Tubing


Pipe is round in shape. It is used for carrying gas and fluid. Pipes are used for transporting gas around your house. They are also used for draining and supplying water to your home.


A tube is round, rectangular, or square in shape. Rectangular and square shape tubing is used in construction as a supporting frame. Refrigerant lines in HVAC systems are made of roundcopper tubing.

The basic difference between a pipe and a tube is their dimension or size. Pipes are available in various sizes based on their inside diameter. Tubes are available based on their outside diameter.


For example, ½ inch pipe will have ½ inch inside diameter. For a ½ inch tube, the outside diameter will be ½ inch.


Pipes and tubes are made of different materials. This makes them suitable for different use. For example, metal pipes and tubes are preferred for high temperature applications. Plastic piping and tubing is used for low temperature application.


Metals have a high melting point. Recall that melting point is the temperature at which a solid substance changes to a liquid.


Due to high melting point of metals, they can withstand high temperature. When we start heating, the pipe slowly starts to appear black and then becomes red. Notice that it does not melt even at a high temperature.


Metal pipes do not lose their form when they are exposed to high heat. So, it is great for high temperature applications. We use metal pipes and tubes in HVAC systems for carrying high temperature refrigerants.


Plastic has a lower melting point. It cannot withstand high temperature. Let us look at the changes that occur in plastic at higher temperatures.


We see pipe becomes yellowish after heating. If we increase the temperature further, it starts to melts. At very high temperature, it appears to be black and catches fire.


Plastic pipes lose their form when they are exposed to high heat. If we use plastic pipe for high temperature application, it will damage the pipe.


The temperature of the air passing through the ductwork is less. This makes plastic pipes suitable for ductwork.


Different types of metals used for HVAC tubes are:

  • Copper, and

  • Steel

Different types of plastic used in HVAC system are:

  • PVC (Polyvinyl chloride), and

  • PEX (Cross-link polyethylene)

Let us discuss about each of them.


Copper


Copper can withstand higher temperature and does not melt easily. Copper can conduct heat easily. It is resistant to corrosion. This means it does not rust when exposed to air.

Recall that HVAC application requires high temperature and heat transfer throughout the cycle. Copper tubing is preferred for refrigerant lines used in HVAC system. Copper offers high heat transfer and can sustain extreme temperature. This makes it the best choice for refrigerant lines.


As copper does not rust, it prevents damage in the pipe and no leakage occurs. It does not release contaminants of copper metal to fluid that it carries. Copper tubes are lightweight. This makes them easy to install.


Steel


Steel is stronger and more durable than other metals. Like copper, steel is resistant to corrosion.

If you look behind your refrigerator you will see steel tubing. Steel is also used in making compressor casing in HVAC. We use steel tubing in HVAC as it is rust free and more durable.


Steel does not react with the fluid it carries. Recall that steel is highly malleable. This means it can be easily hammered into thin sheets. These sheets are used to make ductwork in HVAC systems.


Plastic


Recall that plastic has lower melting point than metals. It cannot be used for heat-related applications. We can use them for ductwork and ventilation piping that does not involve high heat.

If we use metals in vent piping, they can corrode. Corrosion can cause mold and mildew to accumulate in vent pipes. This can restrict the airflow in ventilation piping. Plastic piping offers corrosion resistance which makes it a good option for ductwork.


Plastic piping is also preferred when we install ductwork underground. This is because some soils have a corrosive nature. Plastic piping is suitable as it resists corrosion.


The cost of plastic pipe is very less compared to metal pipe. Plastic piping is less rigid than metals. It can be easily bent unlike metals.


Plastic piping takes lesser time to install than metal piping. This is because, we join two metal pipes using joints and couplers to change the direction of the fluid. Plastic pipes do not need any joints and couplers as we can easily bend them.


Pipe scale is the material that builds up on the inside of pipes. Scale is formed in metal pipes due to reaction with minerals flowing through pipes. Plastic is less reactive to minerals. No scale formation occurs in plastic piping.


The plastic piping used in HVAC system is:

  • PVC - Polyvinyl Chloride

  • PEX - Cross-linked Polyethylene

Each of them has their own properties. Let us learn more about them.


PVC is a rigid pipe. You will have to soften the pipe to bend it to connect other piping. PEX is more flexible. PEX can bend easily without a need for softening. This allows them to have fewer connections, since joints and couplers are not required.


Recall that every solid is made of small molecules. The molecules of PEX material are tightly packed, forming a strong bond amongst them. This makes PEX more durable than PVC.


PEX has the ability to withstand extreme temperature. It can withstand temperature up to 302 ℉. PVC can withstand temperatures up to 180 ℉. PEX tubing is preferred for ductwork that carries air with high temperature.


Pipes and tubes are distinguished by their dimensions. Pipes are available in various sizes based on their inner diameter. Tubes are available based on their outer diameter.


Pipes and tubes are made of metals such as copper and steel. They can be made of plastic such as PVC and PEX. Copper tubes are used for refrigerant lines whereas steel tubes are used for compressor casing. We use plastic pipe for ventilation piping and ductwork.




Pipe Sizing


In this module, we will learn about pipe sizing and methods to determine the length of a pipe. We will also learn about pipe thickness and how to measure a pipe diameter using vernier caliper Skip to quiz!


Pipe Sizing


Before cutting pipes and tubes, we need to determine how much to cut. Let us now look at how to determine the length of pipe used in HVAC.


We use pipes of different lengths in HVAC. The length of the pipe is decided based on the space available for the installation. We measure the space available using a measuring tape.

Once we measure the space needed, we decide the length of the pipe that needs to be trimmed. To understand better, think about your home air conditioner. We need to connect a pipe from the indoor unit to the outdoor unit to carry refrigerant.


The indoor unit of the air conditioning system in your house is present in the basement. The distance from the basement to the outdoor unit is measured. This is how you decide the pipe length based on space available.


Another method to decide the length of the pipe is by reading the blueprint. Blueprint is a map of the HVAC system.


For example, a map of the United States can show you the name and location of each state. Similarly, the blueprint can show you the length and location of the pipe used in the HVAC system.


This image shows the blueprint of the HVAC system. We can see different pipes connected to the central system. Here, they are shown in blue and green color. The length of the green pipe is 12 inches, and that of the blue pipe is 10 inches.


One more important parameter you should know before trimming the pipe is the pipe size. Recall that pipe size tells you about its diameter and its thickness.Knowing this will ensure you are using the correct pipe for the correct application.


Pipe size is specified by its nominal diameter, inside diameter, and outside diameter. Nominal pipe sizes are approximate sizes. They denote a specific size but not an exact inside or outside diameter of the pipe.


Pipe size can also be specified by the pipe schedule. A pipe schedule is a number that relates to the thickness of the pipe, also known as pipe wall thickness. As the schedule number increases, thickness of the pipe increases.


For example, most common pipe schedule is 40. A 1 inch pipe with schedule 40 has a wall thickness of 0.133 inches.


Pipe schedule number is used to classify pipes for high or low pressure and temperature applications. A pipe with a high schedule is preferred for high pressure and high temperature applications. This prevents the cracking of pipe due to high pressure.


We can easily find the relationship between pipe size, pipe schedule, and wall thickness using a conversion chart. You only need to find the inside or the outside diameter of the pipe to know other dimensions of the pipe. You can see the example of a conversion chart in the picture to the right.


For example, we measure the outside diameter of the pipe and observe it to be 1.050 inches. Then we find the outside diameter of 1.050 inches in the pipe schedule chart.


We get all the other dimensions of the pipe. In this case, the nominal pipe size is ¾ inch. It is a schedule 40 pipe of 0.113 inch wall thickness.


Vernier Caliper


The inside and outside diameter can be measured by using a vernier caliper. It has a main scale and a vernier scale to show the exact dimension. Let us look at how to use a vernier caliper.


Before using a caliper, we need to ensure it is error-free. If the calipers are not checked for errors before you begin, then your reading will likely be inaccurate.


To check the error, close the jaws completely and check whether zero on the main scale coincides with zero on the vernier scale. If zeroes on both scales coincide, then no error is present. If they don't coincide, there is an error. We add or subtract this error to get the right measurement.


If the vernier scale is to the right of main scale, we have a positive zero error. If the zero on the main scale lines up with the first division on the vernier scale then we have a positive zero error of 0.1 mm.


We subtract 0.1 mm from all measurements to get the right result. For example, we measure the outside diameter of a pipe as 2.6 mm. By subtracting the error of 0.1 mm, the actual diameter of the pipe will be 2.5 mm.


If the vernier scale is to the left of main scale, we have a negative zero error. If the zero on the main scale coincides with the first division on the vernier scale, we have a negative zero error of 0.1 mm.


We add the error value to get the actual reading. For example, we measure the outside diameter of a pipe as 2.6 mm. By adding the error of 0.1 mm, the actual diameter of the pipe will be 2.7 mm.


The jaws of the vernier caliper are adjustable. To measure the outside diameter of the pipe, open the calipers wider than the outside of the pipe.Then close the jaws around the outer part of the pipe for external measurement.


Vernier caliper can also be used to measure inside diameter. You have to use internal jaws located on the top portion of the calipers.


To measure inside diameter, open the calipers until the inner measurement jaws are pressed against the inside of the object. Read the main scale and vernier scale reading just like we did for measuring the outside diameter. This way we can find the inside diameter of object.


Length of the pipe can be decided based on the space and by using a blueprint. Blueprint is the map of HVAC system that shows the length and the location of a pipe.


A pipe schedule is a number that relates to the thickness of the pipe. We can find the all the dimensions of pipe by measuring inside or outside diameter. Vernier caliper is used to measure both the diameters of the pipe.






Question #1: A tube has only round shape.

  1. False

  2. True

Scroll down for the answer...












Answer: False

Recall that tube is round, rectangular, or square in shape.


Question #2: Pipes are available in various sizes based on _______.

  1. Outside diameter

  2. Inside diameter

  3. Wall thickness

  4. Length

Scroll down for the answer...









Answer: Inside diameter

Pipes are available in various sizes based on their inside diameter.


Question #3: Why metal pipes are used for high temperature applications?

  1. Because of their heat conductivity

  2. Because of high melting point

  3. Because of low boiling point

  4. Because of high pressure

Scroll down for the answer...













Answer: Because of high melting point

Recall that metals have a high melting point.

Metal pipes and tubes are preferred for high temperature applications.


Question #4: Plastic pipe can withstand more temperature than metal pipe.

  1. False

  2. True

Scroll down for the answer...












Answer: False

Recall that plastic has a lower melting point. It cannot withstand high temperature.


Question #5: Plastic is not used in HVAC systems because they can easily melt and catch fire?

  1. False

  2. True

Scroll down for the answer...














Answer: True

Recall that plastic is prone to melt or even catch fire at the high temperatures used in HVAC systems.


Question #6: What does Corrosion Resistant mean?

  1. Can be hammered into shape

  2. Able to heat up and cool down fast

  3. Can be pulled into thin strands

  4. Does not reacts with air to form rust

Scroll down for the answer...














Answer: Does not reacts with air to form rust

Recall that Corrosion Resistant is when a material does not react with air to form rust.


Question #7: Copper is highly resistant to corrosion?

  1. True

  2. False

Scroll down for the answer...














Answer: True

Recall that copper is highly resistant to corrosion and used in areas that are prone to rust.


Question #8: Where do we use plastic piping in HVAC system? (select all that apply)

  1. Condenser

  2. Ductwork

  3. Vent pipe

  4. Refrigerant lines

Scroll down for the answer...














Answer: Ductwork

Vent pipe

Recall that plastic has lower melting point than metals.

We can use them for ductwork and ventilation piping that does not involve high heat.


Question #9: PEX is more flexible than PVC?

  1. True

  2. False

Scroll down for the answer...














Answer: True

Recall that PEX is more flexible. PEX can bend easily without a need for softening.


Question #10: A blueprint shows _________. (Select all that apply)

  1. Location of the pipe

  2. Length of the pipe

  3. Material of the pipe

  4. Temperature of the pipe

Scroll down for the answer...














Answer: Location of the pipe

Length of the pipe

A blueprint is the map of HVAC system.

It shows the length and the location of the pipe used in HVAC system.


Question #11: As the schedule number increases, thickness of the pipe decreases.

  1. True

  2. False

Scroll down for the answer...














Answer: False

A pipe schedule is a number that relates to the thickness of the pipe, also known as pipe wall thickness. As the schedule number increases, thickness of the pipe increases.


Question #12: If the vernier scale is to the left of main scale, we have a positive zero error.

  1. True

  2. False

Scroll down for the answer...














Answer: False

If the vernier scale is to the left of main scale, we have a negative zero error. If the vernier scale is to the right of main scale, we have a positive zero error.



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