The ANSI pipe chart provides standardized dimensions for pipes, including Nominal Pipe Size (NPS), Outside Diameter (OD), Inside Diameter (ID), and wall thickness. These dimensions are crucial for ensuring compatibility and interoperability in piping systems across various industries.
Why Aren’t OD’s Whole Numbers?
The reason OD sizes like 2.375″ and 3.5″ aren’t whole numbers like 2.00″ or 3.00″ is due to historical and practical reasons:
- Historical Evolution: Pipe sizes evolved over time based on the needs of different industries and applications. The nominal sizes were established to standardize the dimensions, but the actual OD often varied to accommodate different wall thicknesses and material strengths.
- Nominal Pipe Size (NPS): NPS is a dimensionless number that corresponds to the pipe’s OD but doesn’t directly equate to it. For example, a pipe with NPS 2″ has an OD of 2.375″, and a pipe with NPS 6″ has an OD of 6.625″. This system allows for a standardized way to denote pipe sizes without being restricted to flat numbers.
How Was the ANSI Pipe Chart Created?
The ANSI pipe chart was developed through collaboration between several standards organizations, including ANSI (American National Standards Institute), ASME (American Society of Mechanical Engineers), and ASTM (American Society for Testing and Materials). Here’s a brief overview of the process:
- Standardization: ANSI accredits standards developed by other organizations, ensuring consistency and safety in piping systems. ASME and ASTM provide detailed guidelines on the design, materials, fabrication, testing, and inspection of pipes.
- Pipe Schedule: The term “pipe schedule” refers to the thickness of a pipe’s wall, which is crucial for determining the pipe’s pressure rating, weight, and mechanical properties. Pipe schedules are denoted as “SCH” followed by a number (e.g., SCH 40, SCH 80), providing a standardized way to specify wall thickness across different diameters.
- Collaboration: ANSI collaborates with ASME to publish standards that ensure the consistency and safety of piping systems. ASTM standards specify the material properties, dimensions, and testing methods for different types of pipes.
These standards and guidelines are compiled into the ANSI pipe chart, providing a comprehensive reference for engineers and designers to select the appropriate pipe size and wall thickness based on project requirements.
Why Do STD Wall and SCH 40 Deviate at Larger OD’s? Same with XH and SCH 80?
The deviation between STD wall and SCH 40, as well as XH and SCH 80, at larger OD’s occurs due to differences in how wall thickness is standardized for larger pipes:
- STD Wall vs. SCH 40: Up to a certain size (typically NPS 10), STD wall and SCH 40 have the same wall thickness. However, beyond this size, SCH 40 wall thickness continues to increase with the pipe size, while STD wall thickness plateaus. This divergence ensures that larger pipes can handle higher pressures and mechanical stresses.
- XH vs. SCH 80: Similarly, XH and SCH 80 have identical wall thicknesses up to NPS 8. Beyond this size, SCH 80 wall thickness increases, while XH wall thickness remains constant. This differentiation allows for higher pressure ratings and mechanical strength in larger pipes.
Do you want a copy of the ANSI Pipe chart?
There’s several ways to get a copy.
- Download a printable version by clicking HERE
- Request an 11″ x 17″ copy from your Omega Steel Sales rep. (if you don’t have a rep, send a request to [email protected])