Schedule 40 Vs 80 steel pipe, Wall thicness and pressure rating

What Is The Nominal Pipe Size?

Before understanding Schedule, we must first grasp what Nominal Pipe Size (NPS) is. Nominal Pipe Size (NPS) is a standardized term used to describe pipe diameter, widely applied in industrial piping systems. NPS does not represent the actual diameter of the pipe but rather an approximate value used to simplify pipe classification and selection.

The NPS value is typically an integer in inches, representing the nominal inside diameter of a pipe. For example, NPS 1 indicates an inside diameter of approximately 1 inch, while NPS 2 indicates an inside diameter of approximately 2 inches. A larger NPS value corresponds to a larger pipe size.

What is a Schedule?

In steel pipe specifications and dimensions, Schedule (SCH) denotes the pipe wall thickness, serving as a key factor in determining the pipe’s pressure rating and strength. A higher Schedule number indicates thicker pipe walls and greater pressure-bearing capacity.

Schedule is a standardized classification associated with NPS. The most common Schedule designations include 10, 20, 40, 80, 160, etc., with each designation corresponding to a specific wall thickness.

Common Schedule Schedule

• Schedule 10：Thinner wall thickness, suitable for low-pressure applications.
• Schedule 40：The most commonly used standard, suitable for medium-pressure applications.
• Schedule 80：Thicker wall thickness, suitable for high-pressure applications.

As the Schedule number increases, the pipe wall thickness also increases accordingly. Users can select the appropriate pipe based on their requirements to meet specific pressure and strength demands.

The standardization of NPS and SCH is primarily established by the American National Standards Institute (ANSI) and the American Petroleum Institute (API). Common standards include:

• ASME B36.10：Standard for seamless steel pipes and welded steel pipes.
• ASME B36.19：Standard for stainless steel pipes.

These standards provide detailed information on the corresponding outer diameters and wall thicknesses for different NPS values. We have compiled a comprehensive library of common standard documents. Click to download.

Schedule 40 and 80 Steel Pipe Wall Thickness and Outside Diameter Table

Compared to Schedule 80, Schedule 40 pipes typically exhibit wall thickness differences ranging from 35% to 70%. Generally, the larger the pipe diameter, the more pronounced the difference becomes.

Pressure Ratings for Schedule 40 and 80

The pressure rating of a pipeline refers to the maximum safe pressure it can withstand internally, typically expressed in PSI (pounds per square inch) or MPa (megapascals). Beyond wall thickness, a pipeline’s pressure rating is also closely related to its material composition and intended application scenario.

ASTM A53/ASTM A106 standards require reference to the pressure-bearing capacity of steel pipes:

1. SCH 40：
   • Rated working pressure:For pipe sizes ranging from NPS 1/2 inch to NPS 24 inches, the rated working pressure typically falls between 150 PSI and 300 PSI, depending on the pipe diameter and material.
   • Hydrostatic Pressure Test:The test pressure is 1.5 times the rated working pressure, typically ranging from 225 PSI to 450 PSI.
2. SCH 80：
   • Rated working pressure:The rated working pressure for pipes ranging from NPS 1/2 inch to NPS 24 inches typically falls between 300 PSI and 600 PSI, depending on the pipe’s diameter and material.
   • Hydrostatic Pressure Test:The test pressure is 1.5 times the rated working pressure, typically ranging from 450 PSI to 900 PSI.

How should Schedule 40 and 80 be selected?

Typically, Schedule 40 pipes are 40%-60% cheaper than Schedule 80 pipes, which offer higher pressure ratings. However, Schedule 80 is not always the optimal choice for every application scenario.

Thicker pipe walls do not guarantee absolute safety. For instance, in marine environments, excessively thick walls may mask internal corrosion, leading to undetectable leaks. This was the cause of the 2022 Abu Dhabi desalination plant incident. Furthermore, at the same nominal pipe size (NPS), SCH40 pipes offer greater flow capacity than SCH80 pipes. Blindly opting for Schedule 80 would necessitate increasing pump power to achieve the same flow rate, indirectly raising costs.

Therefore, selecting between Schedule 40 and Schedule 80 requires consideration of multiple factors, including project budget and actual application scenarios. We recommend contacting our professional team to develop a customized solution tailored to your needs.