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How Is Ductile Iron Pipe Measured?

Jun. 09, 2023

Ductile iron pipe is commonly used in various applications, including water and wastewater systems, due to its durability and strength. When it comes to measuring ductile iron pipe, there are several key parameters and standards that are used. In this guide, we will explore how ductile iron pipe is measured and the important factors to consider.


Nominal Pipe Size (NPS):

The Nominal Pipe Size (NPS) is a standard measurement used to identify the size of a pipe. It represents an approximate internal diameter based on historical conventions rather than actual measurements. NPS is expressed in inches and is commonly used in North America. For example, NPS 4 indicates a pipe with a nominal internal diameter of 4 inches.


Inside Diameter (ID):

The Inside Diameter (ID) refers to the actual internal diameter of the ductile iron pipe. It is measured in inches or millimeters and represents the clear opening through which fluids or materials flow. The ID can vary depending on the pipe's wall thickness, and it is an important factor to consider when determining flow capacity or compatibility with fittings and accessories.

 EN598 Ductile Iron Pipe

  EN598 Ductile Iron Pipe

Outside Diameter (OD):

The Outside Diameter (OD) is the measurement of the outer circumference of the pipe. It is typically larger than the ID due to the thickness of the pipe wall. The OD is measured in inches or millimeters and is essential for determining the pipe's compatibility with fittings, valves, and other components. It is important to note that the OD of ductile iron pipe is not standardized and can vary depending on the manufacturer or specific standards.


Wall Thickness:

The Wall Thickness refers to the distance between the pipe's inner and outer surfaces. It is measured in inches or millimeters and plays a crucial role in determining the pipe's strength and pressure-carrying capacity. The wall thickness can vary depending on the pipe's diameter and the applicable standards or specifications. It is essential to consider the wall thickness when selecting ductile iron pipe for specific applications, especially those involving high-pressure systems.

 ISO2531 Ductile Iron Pipe K9

  ISO2531 Ductile Iron Pipe K9

Pressure Class:

Ductile iron pipe is available in different pressure classes, which indicates the pipe's ability to withstand internal pressure. The pressure class is determined by various factors, including the pipe's diameter, wall thickness, and the material's mechanical properties. Common pressure classes for ductile iron pipe include Class 150, Class 200, Class 250, Class 300, Class 350, and Class 400. The pressure class is typically identified by markings or labels on the pipe.



The Length of ductile iron pipe is another important measurement. It refers to the overall physical length of the pipe and is typically specified in feet or meters. Common lengths for ductile iron pipe range from 18 feet to 20 feet (5.5 meters to 6.1 meters). The specified length is important for accurate installation and determining the number of pipes required for a specific project.


Standard Specifications:

Ductile iron pipe is manufactured according to specific standards and specifications. These standards define the dimensions, materials, quality requirements, and testing methods for ductile iron pipes. Some commonly used standards for ductile iron pipe include the American Water Works Association (AWWA) standards, such as AWWA C151 and AWWA C115, as well as the International Organization for Standardization (ISO) standards, such as ISO 2531 and ISO 7186. These standards provide guidelines for the measurement and manufacturing of ductile iron pipes, ensuring consistent quality and performance.


In conclusion, the ductile iron pipe is measured using various parameters, including the Nominal Pipe Size (NPS), Inside Diameter (ID), Outside Diameter (OD), Wall Thickness, Pressure Class, Length, and adherence to specific standards and specifications.

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