Pipe Schedule Charts : How to Use a Pipe Schedule Chart

Pipes are a critical component in various industries, from construction to oil and gas, where transporting fluids and gases safely and efficiently is paramount. One of the key factors that influence the selection of pipes for these applications is their wall thickness, which directly affects the pipe’s pressure tolerance and flow capacity. This is where pipe schedules come into play.

A pipe schedule refers to a standardized system that specifies the wall thickness of pipes based on their nominal size. It ensures consistency and reliability in pipe manufacturing and installation. Pipe schedule charts are essential tools for engineers, contractors, and manufacturers, providing a quick reference to determine the appropriate pipe schedule needed for a specific application. By understanding and using these charts, professionals can ensure that the selected pipes will handle the required pressures and conditions while meeting industry standards.

In this article, we will explore the concept of pipe schedules, how to read and use pipe schedule charts, and the importance of selecting the correct schedule for different piping systems. Whether you are working on a plumbing system or a large industrial pipeline, understanding pipe schedules is crucial to ensuring the efficiency and safety of the operation.

A pipe schedule is a standardized designation used to define the thickness of a pipe’s wall. While pipes may have the same nominal diameter, the wall thickness can vary, which directly affects the pipe’s ability to handle pressure and the flow of fluids or gases. The term “schedule” represents a system that relates the pipe’s wall thickness to its diameter.

The pipe schedule system was developed by the American National Standards Institute (ANSI) to help ensure consistency across different pipe sizes and materials. It is represented by numbers like Schedule 5, 10, 40, 80, and 160, among others. As the schedule number increases, so does the pipe’s wall thickness, allowing the pipe to withstand higher internal pressures.

Key Elements of a Pipe Schedule:

1. Nominal Pipe Size (NPS): This refers to the approximate diameter of the pipe. However, it does not correspond exactly to the outside diameter (OD) of the pipe, which can vary depending on the schedule.
2. Wall Thickness: The primary aspect defined by the schedule number. Higher schedule numbers indicate thicker walls, which provide greater strength and resistance to pressure.
3. Inside Diameter (ID): As the wall thickness increases, the inside diameter of the pipe decreases, affecting the flow capacity.

Example of a Pipe Schedule:

For a pipe with a nominal size of 2 inches:

• Schedule 40 may have a wall thickness of 0.154 inches.
• Schedule 80, a thicker pipe, may have a wall thickness of 0.218 inches.

The difference in wall thickness allows the Schedule 80 pipe to handle higher pressures than the Schedule 40 pipe, even though they have the same nominal diameter.

Importance of Pipe Schedules:

Pipe schedules are critical in the selection of piping for various applications, as they ensure that pipes can safely withstand the operating pressure and temperature in a system. For instance, pipelines in the oil and gas industry may require pipes with higher schedules to handle high-pressure fluids, while lower schedules may suffice for domestic water supply systems.

By understanding pipe schedules, engineers and technicians can make informed decisions to ensure the safety, efficiency, and durability of piping systems in diverse industries.

II. Understanding Pipe Schedule Charts

A pipe schedule chart is an essential tool that provides a comprehensive reference for determining the wall thickness and dimensions of pipes based on their nominal size and schedule number. It helps engineers, contractors, and technicians to select the correct pipe for their specific needs, ensuring that it can withstand the required pressure and flow rates.

Pipe schedule charts typically list a variety of information for different pipe sizes, such as nominal pipe size (NPS), outside diameter (OD), wall thickness, and inside diameter (ID). Let’s break down these key elements to understand how to read and interpret a pipe schedule chart.

Key Components of a Pipe Schedule Chart:

1. Nominal Pipe Size (NPS):
   • This is the approximate diameter of the pipe, used as a standard reference. It does not necessarily correspond to the actual outer or inner diameter of the pipe, but it provides a consistent point of reference across different pipe sizes and materials.
2. Schedule Number:
   • The schedule number indicates the pipe’s wall thickness. Higher schedule numbers, such as Schedule 80 or 160, represent thicker walls, which allow the pipe to handle higher internal pressures.
3. Outside Diameter (OD):
   • The outside diameter of the pipe remains relatively constant for a given nominal size, regardless of the schedule number. For example, a 2-inch pipe will have the same OD for Schedule 40, 80, or 160 pipes, but the wall thickness and internal diameter will differ.
4. Wall Thickness:
   • The thickness of the pipe wall is one of the most important elements of a pipe schedule chart. As the schedule number increases, the wall thickness also increases. This information is crucial for selecting a pipe that can safely withstand specific pressure conditions.
5. Inside Diameter (ID):
   • The inside diameter decreases as the wall thickness increases. The ID affects the flow capacity of the pipe, as a thicker wall reduces the internal space through which fluids or gases can pass.

Example of Reading a Pipe Schedule Chart:

• In this example, for a nominal pipe size of 2 inches:
  • Schedule 40 has an OD of 2.375 inches, a wall thickness of 0.154 inches, and an ID of 2.067 inches.
  • Schedule 80 has the same OD but a thicker wall (0.218 inches) and a smaller ID (1.939 inches).
  • Schedule 160 further increases the wall thickness to 0.344 inches, reducing the ID to 1.687 inches.

How to Use a Pipe Schedule Chart:

1. Identify the Nominal Pipe Size (NPS): Start by determining the pipe size you need based on the flow requirements or application.
2. Select the Appropriate Schedule: Choose the schedule based on the pressure and temperature the pipe must handle. Higher pressures or harsher environments typically require higher schedules (e.g., Schedule 80 or 160).
3. Check the Wall Thickness: Review the wall thickness for the selected schedule and ensure it meets the application’s requirements.
4. Consider the Inside Diameter (ID): Ensure that the ID is large enough to allow the necessary flow rates for your system.

Importance of Using Pipe Schedule Charts:

• Safety: Properly selecting a pipe with the correct wall thickness ensures the pipe can handle the pressure and temperature conditions of the system, reducing the risk of failure.
• Efficiency: Selecting a pipe with an optimal ID allows for efficient fluid or gas flow, preventing pressure drops or system inefficiencies.
• Cost-Effectiveness: Choosing the right pipe schedule ensures that you are not over-designing (using unnecessarily thick pipes) or under-designing (using pipes that cannot handle the required pressures), which helps optimize material costs and system longevity.

By using a pipe schedule chart effectively, engineers and designers can make informed decisions about the pipes needed for their projects, balancing safety, performance, and cost.

III. How to Use a Pipe Schedule Chart

A pipe schedule chart is a valuable tool that helps professionals select the appropriate pipe for a given application by considering factors like pressure, temperature, and flow rate. Here’s a step-by-step guide on how to use a pipe schedule chart effectively:

1. Identify the Nominal Pipe Size (NPS)

• Start by determining the nominal pipe size required for your project. The nominal pipe size (NPS) is a standardized term that refers to the approximate diameter of the pipe. For instance, you may be working with a 2-inch or 4-inch nominal pipe size.
• It’s important to note that NPS does not directly correspond to the actual outer or inner diameter of the pipe but serves as a general reference.

2. Determine the Operating Pressure and Temperature

• Understand the pressure and temperature conditions the pipe will be exposed to. Higher pressures require pipes with thicker walls to prevent failure. For example, if your system involves high-pressure steam or gas, you will need a higher schedule number (such as Schedule 80 or Schedule 160).
• Also, take into account the temperature conditions. High temperatures can affect the pipe’s strength, so ensure the selected pipe schedule can withstand both pressure and temperature requirements.

3. Select the Appropriate Pipe Schedule

• Once you know the nominal pipe size and operating conditions, use the pipe schedule chart to select the correct schedule. The schedule number (e.g., Schedule 40, 80, or 160) represents the thickness of the pipe wall.
• For example, Schedule 40 is commonly used for lower-pressure applications, while Schedule 80 and 160 are chosen for higher-pressure or industrial settings.
• As the schedule number increases, the wall thickness becomes greater, enhancing the pipe’s ability to handle pressure.

4. Check the Wall Thickness

• Refer to the pipe schedule chart to find the wall thickness corresponding to the selected schedule and nominal pipe size. The chart will list the wall thickness in inches or millimeters.
• Ensure that the wall thickness meets your pressure and safety requirements. For instance, if a 2-inch pipe with Schedule 40 has a wall thickness of 0.154 inches, but you need more strength, you might select Schedule 80, which has a wall thickness of 0.218 inches for the same nominal size.

5. Evaluate the Inside Diameter (ID)

• The inside diameter (ID) of the pipe is crucial for determining the flow capacity. As the wall thickness increases with higher schedules, the ID decreases.
• If your system requires a specific flow rate, ensure the ID is sufficient to allow that flow. For instance, in fluid systems, a smaller ID could lead to reduced flow or higher pressure drops, which can affect system performance.
• Verify that the selected schedule allows for adequate flow while still meeting the necessary pressure and temperature specifications.

6. Consider the Outside Diameter (OD)

• While the outside diameter (OD) of pipes typically remains constant for a given nominal size, it is important to check it for space constraints or compatibility with other system components.
• The OD will remain the same regardless of the schedule, so whether you choose Schedule 40 or 80, the pipe’s OD will be consistent for the same NPS.

7. Select the Material of the Pipe

• While the pipe schedule chart primarily deals with size and thickness, the material of the pipe also plays a critical role. The same schedule may have different strength and pressure capacities depending on whether the pipe is made of steel, stainless steel, PVC, or another material.
• Ensure that the material selected is compatible with the operating conditions, such as corrosion resistance or temperature sensitivity.

8. Review Safety and Regulatory Requirements

• Ensure that the selected pipe schedule meets any relevant industry standards and safety codes (e.g., ASME, ANSI, ASTM) for your project.
• Review the local regulations and specifications to make sure the pipes are compliant with any pressure, temperature, or material restrictions that may apply to your industry or region.

Example: Using a Pipe Schedule Chart

Let’s say you’re working on a project that requires 2-inch diameter pipes, and the system will operate at a pressure of 1,000 psi. You would:

1. Look up 2-inch pipes in the pipe schedule chart.
2. Review the wall thickness and inside diameter for various schedules (e.g., Schedule 40, 80, or 160).
3. Based on the high-pressure requirement, select Schedule 80, which offers a thicker wall (0.218 inches) compared to Schedule 40 (0.154 inches).
4. Check the ID to ensure it will allow sufficient flow for your system, confirming that the reduced ID in Schedule 80 still meets the flow requirements.

Using a pipe schedule chart helps ensure that the selected pipes will handle the specific demands of your application, whether it’s fluid transport, gas piping, or industrial systems. By following the steps outlined above, you can select the right pipe schedule to meet safety, pressure, temperature, and flow requirements. Proper pipe selection helps avoid potential failures, costly repairs, or safety hazards down the line.

IV. Common Pipe Schedules

Pipe schedules are standardized numbers that specify the wall thickness of pipes for different applications. The most common pipe schedules vary depending on the type of material and the pressure and temperature requirements of the system. Below are some of the most frequently used pipe schedules and their typical applications:

1. Schedule 5

• Wall Thickness: Thin wall
• Application: Low-pressure applications, such as HVAC and plumbing systems for drainage or venting.
• Material: Often used with stainless steel and other corrosion-resistant materials.
• Advantages: Lighter weight and lower cost due to thinner walls.
• Disadvantages: Limited ability to handle higher pressures and temperatures.

2. Schedule 10

• Wall Thickness: Slightly thicker than Schedule 5
• Application: Low-pressure systems such as chilled water systems, food and beverage processing, and chemical processing.
• Material: Commonly used in stainless steel piping for corrosion resistance.
• Advantages: Lightweight and cost-effective for low-pressure applications.
• Disadvantages: Not suitable for high-pressure or high-temperature applications.

3. Schedule 40

• Wall Thickness: Medium wall thickness
• Application: General-purpose piping in residential, commercial, and industrial applications. Used in water supply lines, irrigation, and low- to medium-pressure fluid transport.
• Material: Available in a wide range of materials, including PVC, carbon steel, and stainless steel.
• Advantages: Versatile and widely used, suitable for a variety of applications at moderate pressures.
• Disadvantages: May not be sufficient for high-pressure industrial processes.

4. Schedule 80

• Wall Thickness: Thicker than Schedule 40
• Application: High-pressure systems such as industrial fluid handling, steam piping, and compressed air systems. Used in oil and gas, chemical processing, and power plants.
• Material: Available in materials like steel, stainless steel, and PVC.
• Advantages: Increased strength and pressure capacity compared to Schedule 40.
• Disadvantages: Heavier and more expensive due to the thicker walls.

5. Schedule 160

• Wall Thickness: Very thick walls
• Application: Extremely high-pressure applications, such as in oil and gas refineries, high-pressure steam systems, and heavy-duty industrial equipment.
• Material: Primarily used with steel and stainless steel pipes.
• Advantages: High durability and resistance to extreme pressures.
• Disadvantages: Very heavy, costly, and difficult to work with due to the thick walls.

6. XXS (Double Extra Strong)

• Wall Thickness: The thickest standard pipe schedule available
• Application: Specialized for ultra-high-pressure systems, often seen in heavy industrial settings and critical applications like hydraulic piping.
• Material: Typically used in carbon steel and stainless steel.
• Advantages: Offers maximum strength and pressure resistance.
• Disadvantages: Extremely heavy and expensive, often over-engineered for typical applications.

Comparison of Common Pipe Schedules:

Understanding the differences between common pipe schedules allows you to select the appropriate pipe for your system’s pressure and temperature requirements. For general applications, Schedule 40 or 80 are the most widely used, while more specialized systems may require the extra strength of Schedule 160 or XXS. Choosing the right schedule ensures the longevity and safety of your piping system.

V. Factors Affecting Pipe Schedule Selection

Selecting the appropriate pipe schedule for a specific application is crucial for ensuring that the piping system can handle the operating conditions and requirements. Several key factors influence the choice of pipe schedule, each of which plays a critical role in the safety, efficiency, and cost-effectiveness of the system. Below are the main factors to consider when selecting a pipe schedule:

1. Operating Pressure

• Description: The higher the operating pressure within a piping system, the thicker the pipe walls need to be to handle the internal pressure without failing.
• Impact: Pipes with higher schedules (such as Schedule 80, 160, or XXS) are designed to withstand greater pressures due to their increased wall thickness. Low-pressure applications, on the other hand, can use pipes with thinner walls, such as Schedule 10 or Schedule 40.
• Example: In high-pressure steam or gas pipelines, thicker schedules like Schedule 80 or 160 are required to prevent pipe rupture.

2. Operating Temperature

• Description: Temperature also affects the pipe material’s strength. High temperatures can reduce a material’s tensile strength, making thicker walls necessary to maintain system integrity.
• Impact: In high-temperature environments, pipes must not only handle the pressure but also remain stable under thermal stress. This is especially important in industrial settings where pipes may be exposed to steam or hot fluids.
• Example: A steam pipeline in a power plant may require pipes with higher schedules, such as Schedule 80 or 160, to maintain durability under both pressure and heat.

3. Corrosiveness of the Fluid

• Description: If the fluid or gas passing through the pipe is corrosive (e.g., acids, chemicals, saltwater), it can wear down the internal walls of the pipe over time.
• Impact: Thicker pipes or those made from corrosion-resistant materials are typically required in corrosive environments. Additionally, higher schedules are sometimes selected to provide extra thickness as a buffer against corrosion.
• Example: In chemical processing plants where pipes may carry corrosive liquids, Schedule 80 or 160 pipes made of stainless steel may be selected to resist corrosion and ensure longevity.

4. Flow Rate

• Description: The flow rate of fluids through the pipe affects the required pipe size and schedule. As the wall thickness increases, the inside diameter (ID) decreases, which impacts the flow capacity of the pipe.
• Impact: For systems that require high flow rates, a thinner schedule might be preferred to maintain a larger internal diameter. However, if pressure is a concern, a balance between flow capacity and wall thickness must be considered.
• Example: In a water distribution system, Schedule 40 pipes might be chosen for their balance of adequate wall thickness and sufficient flow capacity.

5. Material of the Pipe

• Description: Different materials have varying strength, flexibility, and resistance to environmental factors like corrosion and heat.
• Impact: The pipe material influences the schedule selection because certain materials (such as carbon steel, stainless steel, or PVC) have different pressure and temperature tolerances. For example, PVC pipes may require a thicker wall schedule to handle pressure compared to steel pipes.
• Example: Stainless steel pipes used in chemical plants often require higher schedules, such as Schedule 80, due to their ability to handle corrosive environments and high pressure.

6. Piping Application

• Description: The intended use of the piping system greatly influences the pipe schedule. Different industries, such as plumbing, oil and gas, chemical processing, or HVAC systems, have varying demands based on fluid types, system size, and regulatory requirements.
• Impact: Each industry has specific standards and codes that dictate which pipe schedules should be used in certain applications. Industrial applications generally require higher schedules for safety and durability, while residential or low-pressure applications may use lower schedules.
• Example: In residential plumbing, Schedule 40 PVC pipes are commonly used due to their cost-effectiveness and ability to handle low-pressure water systems.

7. Cost Considerations

• Description: Thicker pipes (higher schedules) are more expensive due to the additional material required for manufacturing.
• Impact: While selecting a higher schedule improves strength and pressure handling, it also increases the cost. The selection should balance the need for safety and performance with budget constraints.
• Example: For a low-pressure, non-critical application, selecting Schedule 10 or 40 instead of Schedule 80 can significantly reduce costs without compromising system performance.

8. Standards and Codes

• Description: Industry-specific standards, such as those set by the American Society of Mechanical Engineers (ASME), the American Petroleum Institute (API), and the American National Standards Institute (ANSI), provide guidelines on which pipe schedules to use based on pressure and temperature requirements.
• Impact: Compliance with these standards is mandatory in many industries to ensure safety and consistency. These codes also help determine the minimum required pipe schedule for specific applications.
• Example: In an oil refinery, pipes used in high-pressure steam systems must comply with ASME standards, often requiring pipes of Schedule 80 or higher.

Selecting the appropriate pipe schedule depends on a combination of factors, including operating pressure, temperature, material, flow rate, and application. Understanding these factors ensures that the selected piping system is safe, cost-effective, and durable under the specific conditions it will encounter. Balancing these factors leads to the optimal performance and longevity of the piping system, minimizing the risk of failures or costly repairs.

VI. Examples of Pipe Schedule Chart

Below are two examples of common pipe schedule charts, demonstrating how to read the dimensions of pipes across different schedules for a given nominal pipe size. These charts illustrate the relationship between nominal pipe size (NPS), wall thickness, outside diameter (OD), and inside diameter (ID) for different schedules.

Example 1: Pipe Schedule Chart for Steel Pipes (2-inch Nominal Size)

In this example, the outside diameter (OD) remains constant at 2.375 inches for a nominal 2-inch pipe, regardless of the schedule. However, as the schedule increases (from 10 to 160), the wall thickness also increases, resulting in a reduced inside diameter (ID).

• Schedule 10: Thin-walled pipe, commonly used in low-pressure applications with a wall thickness of 0.083 inches and an inside diameter of 2.209 inches.
• Schedule 40: A standard for general-purpose use, with a wall thickness of 0.154 inches and an inside diameter of 2.067 inches.
• Schedule 80: Thicker walls for higher-pressure applications, with a wall thickness of 0.218 inches and an inside diameter of 1.939 inches.
• Schedule 160: Extra thick walls for high-pressure applications, with a wall thickness of 0.344 inches and an inside diameter of 1.687 inches.

Example 2: Pipe Schedule Chart for PVC Pipes (3-inch Nominal Size)

For a 3-inch nominal pipe size:

• Schedule 40 has a wall thickness of 0.216 inches and an inside diameter of 3.068 inches.
• Schedule 80 has a thicker wall at 0.300 inches, reducing the inside diameter to 2.900 inches.
• Schedule 160 is designed for high-pressure systems, with a wall thickness of 0.438 inches, leaving an inside diameter of 2.624 inches.

How to Read the Chart:

• Nominal Pipe Size (NPS): The nominal reference size of the pipe (2 inches, 3 inches, etc.), which is not the exact outside diameter.
• Schedule Number: Indicates the pipe wall thickness. Higher schedules correspond to thicker walls, which provide greater strength and pressure resistance.
• Outside Diameter (OD): The external dimension of the pipe, which remains constant for a given NPS.
• Wall Thickness: The thickness of the pipe wall. As the schedule number increases, so does the wall thickness.
• Inside Diameter (ID): The internal dimension of the pipe, which decreases as the wall thickness increases. The ID affects the flow capacity of the pipe.

These examples show how a pipe schedule chart is structured and how different schedules impact the dimensions and strength of the pipe. By understanding how to read these charts, professionals can ensure they select the correct pipe schedule for their specific application, balancing pressure, flow rate, and material costs.

Conclusion

Pipe schedule charts play a crucial role in the selection and design of piping systems across various industries. Understanding pipe schedules, and how to read and interpret pipe schedule charts, ensures that the correct pipe dimensions and wall thickness are selected to handle specific pressure, temperature, and flow conditions. These charts help professionals, from engineers to contractors, make informed decisions about the appropriate schedule for different applications, ensuring safety, efficiency, and cost-effectiveness.

Choosing the right pipe schedule is essential for the longevity and reliability of a system. For low-pressure applications, lighter schedules such as Schedule 10 or 40 are often sufficient, while high-pressure and high-temperature environments may require thicker schedules like Schedule 80, 160, or even XXS. Additionally, factors such as material type, corrosive environments, and regulatory standards must be considered when selecting a pipe schedule.

In conclusion, a solid understanding of pipe schedule charts allows for the optimal design and installation of piping systems, reducing the risk of failure and ensuring the system meets operational requirements. Proper pipe selection is not just about fitting pipes into a system but ensuring long-term safety and performance.

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