ASME B16.5 Flanges Standard

ASME B16.5 flanges are available in the following standard pressure classes:

1. Class 150
2. Class 300
3. Class 400
4. Class 600
5. Class 900
6. Class 1500
7. Class 2500

These classes define the maximum allowable pressure the flange can withstand at various temperatures. Selection depends on design pressure, temperature, and material. For example, a Class 600 flange made of carbon steel may have a different pressure-temperature rating compared to one made from stainless steel. Always refer to ASME B16.5 pressure-temperature charts for accurate selection.

Tolerances specified in ASME B16.5—even for outer diameter, flange thickness, bolt-hole spacing, and face flatness—aren’t just arbitrary limits; they ensure interchangeability, proper alignment, and seal integrity across piping components.

Why Tolerances Matter:

• Diameter & Bolt Circle Tolerance

  Ensures exact bolt-hole alignment during assembly, preventing stresses or flange distortion during bolt-up. For flanges under 24″ OD, tolerances may be ±1/16″ (≈1.6 mm), ensuring smooth fitting

• Thickness & Hub Dimensions

  Prevents under-thickness or excessive machining—critical for pressure containment. Thicker flanges risk extra material cost; thinner ones risk strength loss .

• Surface Finish & Face Flatness

  Proper finish (e.g., spiral-serrated or concentric-smooth) and flatness prevent uneven gasket compression, avoiding leakage or blowout—especially in high-pressure applications

• Why Not Tighter Than Specified?

  ASME intentionally defines tolerances based on the least accurate yet practical manufacturing methods. Tighter dims don’t yield better seal—in fact, they increase cost and complexity without adding safety

Selecting the correct ASME B16.5 flange involves evaluating several key factors to ensure compatibility, safety, and efficiency in your piping system:

Key Selection Criteria:

1. Nominal Pipe Size (NPS): Choose the correct size as per the connected piping
2. Pressure Class: Match the pressure rating (e.g., Class 150, 300, 600, etc.) to system pressure and temperature requirements
3. Flange Type: Pick based on connection method — e.g., Weld Neck for high pressure, Slip-On for low pressure, Blind for isolation
4. Face Type: Ensure proper sealing by selecting RF, FF, or RTJ based on gasket and media
5. Material Grade: Choose a flange material compatible with pipe material and fluid (e.g., ASTM A105, A182 F304, etc.)
6. Standard Compliance: Ensure full compliance with ASME B16.5 dimensions and tolerances

Always refer to engineering design data and project specifications to make an informed flange selection that ensures long-term performance and compliance.

While both ASME B16.5 and ASME B16.47 cover flanged components, they differ mainly in terms of size range, application scope, and dimensional standards:

ASME B16.5 is used for standard-sized piping, while ASME B16.47 is specialized for large diameter flanges often used in heavy industrial installations.

The pressure-temperature (P–T) ratings in ASME B16.5 are critical because they define how much pressure a flange can safely withstand at a given temperature. These ratings vary based on:

Key Factors:

• Material of Construction: Different materials (e.g., ASTM A105, A182 F304, F316) have different strength properties at high temperatures.
• Flange Class: Higher class ratings (like Class 1500 or 2500) can handle greater pressures.
• Temperature: As temperature increases, the allowable pressure decreases for any given flange material.
• Gasket Type & Bolting: The combination of gaskets and bolts affects how the flange handles internal pressure under heat.

For example:

• A Class 300 flange in ASTM A105 carbon steel has a pressure rating of 740 psi at 100°F, but only 260 psi at 800°F.
• These values are published in pressure-temperature rating charts within the ASME B16.5 standard.

Always refer to the ASME P–T chart during design to ensure the selected flange meets both operational and safety requirements.

Nutech Overseas is a trusted manufacturer and global exporter of ASME B16.5 flanges, serving industries across multiple continents. We supply flanges to EPC contractors, oil & gas firms, and industrial users in:

• United Arab Emirates (UAE) – Dubai, Abu Dhabi, Sharjah
• Saudi Arabia – Dammam, Riyadh, Jeddah
• Qatar – Doha
• Oman – Muscat, Sohar
• Kuwait – Kuwait City
• Bahrain
• Europe – Germany, Italy, Netherlands, Spain
• USA & Canada
• South East Asia – Philippines, Malaysia, Singapore
• Africa – Egypt, Nigeria, South Africa

We provide custom markings, export-grade packaging, and complete documentation in compliance with international shipping and inspection standards.