Understanding ANSI Flange Standards in Marine and Industrial Applications

Flanges are a critical component in piping systems, providing secure connections for valves, pumps, and pipes. Selecting the correct flange standard is vital to ensure safety, compatibility, and durability in demanding environments such as shipbuilding, offshore, oil & gas, petrochemical, and power generation.

One of the most widely used standards worldwide is the ANSI (American National Standards Institute) flange standard, which has now largely aligned with ASME (American Society of Mechanical Engineers) standards. In practice, the terms ANSI flanges and ASME flanges are often used interchangeably.

As a trusted Singapore-based stockist and distributor, Aik Soon Hardware Pte Ltd supplies ANSI flanges for a wide range of marine and industrial valve applications. In this article, we’ll cover the common ANSI flange standards, the key differences, and how to select the right one for your piping system.

What Are ANSI Flanges?

ANSI flanges are designed based on standards that define dimensions, pressure ratings, materials, and testing requirements. These standards ensure uniformity and allow flanges, valves, and piping components to be safely connected, even if sourced from different manufacturers.

They are extensively used in:

• Marine engineering – cooling systems, fuel oil, ballast water, steam lines

• Oil & gas and petrochemicals – high-pressure and corrosive service lines

• Industrial plants – HVAC, water treatment, chemical processing

Common ANSI Flange Standards

The most common ANSI/ASME flange standards include:

1. ASME B16.5 – Pipe Flanges and Flanged Fittings

• Covers flanges from ½ inch to 24 inches in size.

• Pressure classes: Class 150, 300, 400, 600, 900, 1500, and 2500.

• Commonly used in oil & gas pipelines, refineries, and marine piping systems.

2. ASME B16.47 – Large Diameter Flanges

• Covers flanges 26 inches to 60 inches.

• Split into two series: Series A (formerly MSS SP-44) and Series B (formerly API 605).

• Used in large-diameter industrial and offshore systems.

3. ASME B16.1 – Cast Iron Pipe Flanges

• Used for non-critical, low-pressure applications such as waterworks or HVAC.

4. ASME B16.36 – Orifice Flanges

• Special flanges with holes to measure fluid flow rates.

• Common in process industries where monitoring flow is essential.

Key Differences in ANSI Flange Standards

1. Pressure Classes

   • ANSI flanges are categorized by pressure ratings (Class 150 to 2500).

   • The higher the class, the greater the pressure and temperature capacity.

2. Dimensional Variations

   • ANSI/ASME standards specify thickness, bolt circle diameter, and bolt hole size, ensuring interchangeability.

3. Material Options

   • Available in carbon steel, stainless steel, alloy steel, cast iron, etc., depending on the service medium (e.g., seawater, oil, steam, chemicals).

4. Regional Use

   • ANSI flanges are dominant in North America and globally in oil & gas projects, whereas JIS flanges are more common in Asia and DIN/EN in Europe.

How to Pick the Right ANSI Flange Standard

Choosing the right ANSI flange standard requires careful consideration of:

1. System Design Code

   • Confirm whether your piping design is based on ASME/ANSI, JIS, or DIN/EN. Mixing standards can cause mismatched bolt holes or sealing issues.

2. Pressure and Temperature Requirements

   • Match the flange pressure class with system requirements.

   • Example: Class 150 for low-pressure water lines, Class 600+ for high-pressure steam or oil systems.

3. Material Compatibility

   • For seawater: stainless steel or duplex stainless steel.

   • For hydrocarbons: carbon steel or alloy steel.

4. Size and Dimensional Checks

   • Verify nominal pipe size (NPS), bolt circle diameter (BCD), and gasket requirements.

5. Trusted Supplier Support

   • Working with an experienced distributor like Aik Soon Hardware ensures you get the correct ANSI flange for your project, minimizing risks of downtime or safety hazards.

Conclusion

ANSI (ASME) flange standards are critical for ensuring safe, reliable, and compatible connections in piping systems across marine, offshore, oil & gas, and industrial applications. By understanding the common standards (ASME B16.5, B16.47, B16.1, B16.36), knowing the differences, and evaluating your system requirements, you can confidently select the right flange for your project.

At Aik Soon Hardware Pte Ltd, we provide a comprehensive range of ANSI-standard flanges and valves in Singapore, backed by expertise and a strong track record in serving marine and industrial customers.