ASME B16 Flanges: Types, Standards, Dimensions & Pressure Ratings

In industrial piping systems, ASME B16.5 Flanges play a crucial role in ensuring leak-proof connections and structural integrity. The ASME (American Society of Mechanical Engineers) B16 series defines flange standards for different pressure classes, materials, and dimensional specifications.

Whether you're selecting ASME B16.5, B16.47, or B16.48 flanges, understanding the flange classifications, pressure ratings, and material types is critical for ensuring optimal performance. This guide will help you navigate the ASME flange standards and choose the right flange for your application.

The ASME B16 standard flanges are a set of pipe flange specifications developed by ASME for use in industrial piping systems. These standards cover different aspects such as:

✔ Flange dimensions (diameter, thickness, bolt holes)
✔ Pressure-temperature ratings
✔ Materials and manufacturing processes
✔ Installation guidelines

Each subcategory of ASME B16 flanges caters to different applications and pressure ratings.

ASME B16.5 and B16.47 flanges are categorized into a wide range of different pressure classes, which indicate the maximum pressure the flange can handle at a given temperature. The pressure class directly affects flange thickness, bolt hole size, and material strength.

A flange class represents a pressure rating in pounds per square inch (psi) under normal temperature conditions. Higher-class flanges withstand greater pressure and higher temperatures before failure.

• Used for: General piping, water lines, low-pressure steam
• Material Options: Carbon steel, stainless steel, cast iron
• Example Applications: HVAC systems, low-pressure oil pipelines

• Used for: Moderate pressure steam, process industries
• Example Applications: Industrial water supply, chemical processing

• Used for: High-pressure steam and oil & gas pipelines
• Example Applications: Refineries, high-temperature steam systems

• Used for: Heavy industrial, power plants, offshore oil rigs
• Example Applications: Nuclear plants, high-pressure chemical transport

The Following charts show the trend of maximum allowable working pressure at a given temperature across classes:

Covers pipe flanges and flanged fittings from ½ inch to 24 inches in diameter and is the most widely used ASME flange standard in industries such as oil & gas, chemical processing, and power plants.
• Pressure classes: 150, 300, 400, 600, 900, 1500, 2500
• Common materials: Carbon steel, stainless steel, alloy steel

Designed for pipe sizes 26 inches to 60 inches, this standard is further divided into two series:
• Series A (MSS SP-44 Flanges) – Higher strength and thicker
• Series B (API 605 Flanges) – Lighter and cost-effective

Used for isolating piping sections, these flanges help in maintenance and pipeline shutdowns.

• Best for: High-pressure and high-temperature applications.
• Description: Features a long, tapered hub that reinforces the connection and minimizes stress, best flange for handling thermal expansion and cyclic loading.
• Usage: Ideal for critical applications like oil & gas, petrochemical, and power plants.

• Best for: Low-pressure applications and easy installation.
• Description: The pipe slides into the flange and is fillet-welded on both sides.
• Usage: Used in low-pressure water, gas, and air systems.

• Best for: Small-diameter, high-pressure applications.
• Description: The pipe fits into a socket and is fillet-welded at the top.
• Usage: Common in high-pressure steam, chemical, and hydraulic systems.

• Best for: Low-pressure, non-welded connections.
• Description: Has internal threads to screw onto externally threaded pipes.
• Usage: Suitable for applications where welding is not feasible, such as explosive environments.

• Best for: Systems requiring frequent disassembly.
• Description: Works with a stub end, allowing rotation for easy alignment.
• Usage: Common in piping systems requiring frequent cleaning, such as in food processing.

• Best for: Sealing pipe ends or isolating sections of piping.
• Description: A solid disk that blocks off a pipe.
• Usage: Used in maintenance shutoffs and pressure testing.

Selecting the correct ASME flange type and material depends on multiple factors:

Flange Size & Pressure Class
• Smaller pipes (≤24 inches) → Use ASME B16.5
• Larger pipes (>24 inches) → Use ASME B16.47
• Higher pressure (600–2500 class) → Prefer weld neck flanges


 Material Selection
• Carbon Steel → High strength, cost-effective, used in oil & gas
• Stainless Steel → Corrosion-resistant, used in chemical industries, encompasses many types of steel, good mechanical properties and resistance to corrosion.
• High Alloy Steel → Heat-resistant, used in power plants and other industrial applications, good wear resistance, has alloying elements added.


 Face Type & Connection
• Raised Face (RF) → Improves sealing (most common)
• Flat Face (FF) → Used in low-pressure applications
• Ring Type Joint (RTJ) → For high-pressure, high-temperature environments

Please see general flow chart below to determine the type of connection that may be best for your needs. Always confirm with standards that your selection will meet your needs:

Understanding ASME B16 flanges, their classifications, flange pressure ratings, and material types is essential for designing robust industrial piping systems. Whether you need ASME B16.5, B16.47, or B16.48 flanges, ensure your selection aligns with pressure requirements and application needs.
By following ASME flange standards, industries can maintain safety, efficiency, and long-term performance in their piping networks.