In the pipe and flange industry, the terms ANSI flange and ASME B16.5 flange are often used interchangeably. Many buyers, engineers, and suppliers use these names synonymously, which raises a common question: “Are ANSI and ASME B16.5 flanges the same standard?”
The short answer is no—but they are closely related. This article breaks down the real distinction between ANSI and ASME B16.5, explains why the confusion exists, and outlines how these terms are typically used in purchasing, engineering, and production.
What is ANSI?
A key point to clarify upfront: ANSI is not a flange standard.
ANSI stands for American National Standards Institute, an organization that approves and recognizes standards developed by other technical bodies. ANSI does not:
- Establish flange dimensions
- Set pressure ratings
- Outline material requirements
- Create flange design guidelines
ANSI’s primary role is to review, approve, and coordinate standards across various industries, with no specific focus on pipe flanges.
What is ASME B16.5?
ASME stands for American Society of Mechanical Engineers, and ASME B16.5 is the official, globally recognized standard for pipe flanges and flanged fittings.
This standard covers a range of key specifications, including:
- Nominal pipe sizes from NPS 1/2 to NPS 24
- Pressure classes: Class 150, 300, 600, 900, 1500, and 2500
- Flange types: Weld Neck, Slip-On, Blind, Threaded, Socket Weld, Lap Joint
- Facing types: RF, FF, RTJ, M/FM, TG
- Pressure-temperature ratings
- Material specifications
- Tolerances and marking requirements
For industrial flanges, ASME B16.5 serves as the primary technical reference.
Confusion Between ANSI and ASME B16.5
The overlap between these terms stems from historical context and industry tradition.
In earlier iterations, the flange standard was officially published as ANSI B16.5. Over time, ASME took over full responsibility for developing and updating the standard, and its current official name is:
ASME B16.5 Pipe Flanges and Flanged Fittings
Even so, the term “ANSI flange” became so widespread that it remains in common use today.
To simplify:
- Historical name: ANSI B16.5
- Current official name: ASME B16.5
This is why both terms appear regularly in catalogs, websites, and customer requests.
Key Distinctions Between ANSI and ASME B16.5
Below is a summary of the key differences to provide clarity:
- ANSI is an organization, while ASME B16.5 is a standard.
- ANSI does not develop flange specifications—ASME B16.5 defines all technical requirements.
- “ANSI flange” is a common industry term, not an official standard designation.
- For manufacturing and certification, ASME B16.5 is the standard most commonly referenced.
In design, ordering, or inspection processes, ASME B16.5 is the typical reference point for flanges.
Can ANSI and ASME B16.5 Flanges Be Used Interchangeably?
Yes—they are fully interchangeable in practical applications.
When a customer requests:
- “ANSI Class 150 flanges”
- “ANSI B16.5 weld neck flanges”
They are generally seeking flanges that meet the ASME B16.5 standard.
Flanges manufactured to ASME B16.5 can be safely supplied in these cases, as they will fit and perform as expected. There is no compatibility issue, since both terms refer to the same design and dimensions.
How to Use the Terms
In day-to-day communication:
- “ANSI flange” is widely understood and acceptable for general reference.
For technical documents, drawings, purchase orders, and certifications:
- ASME B16.5 is the preferred and official term.
Using the official name in technical contexts helps ensure clarity and professionalism.
Conclusion
ANSI and ASME B16.5 flanges are not the same standard.
- ANSI is an organization that approves standards.
- ASME B16.5 is the official standard for pipe flanges.
- “ANSI flange” is a widely used industry term, not a formal standard.
- In purchasing and production, ASME B16.5 is the standard typically followed.
In short, when you encounter the terms “ANSI flange” or “ANSI B16.5 flange,” they almost always refer to flanges that conform to ASME B16.5.