Valve End Connections and Mating Flanges: A B16.34 and B16.5 Buying Guide

When you specify a flanged valve, you are actually specifying two separate components that must work together: the valve itself and the mating flange. Each is governed by its own ASME standard, and compliance with one does not guarantee compatibility with the other. This guide explains the roles of ASME B16.34 and ASME B16.5, and provides a practical procurement checklist to ensure your valve-flange pairs are correctly matched.

The Two Standards: What Each Covers

ASME B16.34 – Valves—Flanged, Threaded, and Welding End

ASME B16.34 applies to new construction of valves with flanged, threaded, or welding ends. It covers pressure-temperature ratings, dimensions, tolerances, materials, nondestructive examination requirements, testing, and marking for cast, forged, and fabricated valves made of steel, nickel-base alloys, and other alloys. Importantly, wafer or flangeless valves that are installed between flanges or against a flange are treated as flanged-end valves under this standard. The standard also provides alternative rules for valves NPS 2½ and smaller.

ASME B16.5 – Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24

ASME B16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings. It includes flanges with rating class designations 150, 300, 400, 600, 900, and 1500 in sizes NPS 1/2 through NPS 24, and class 2500 in sizes NPS 1/2 through NPS 12. The standard also covers flanged fittings with rating classes 150 and 300 in sizes NPS 1/2 through NPS 24, and provides requirements for bolting, gaskets, and flange joints.

Why Compliance with One Standard Isn’t Enough

A valve may be fully compliant with ASME B16.34, and a flange may be fully compliant with ASME B16.5, but that does not automatically mean they will bolt together correctly. Several parameters must be verified to ensure a proper match:

• Pressure class: The flange class (e.g., 150, 300, 600) must match the valve’s pressure class. Mismatched classes can lead to leakage or structural failure.
• Material group: Both components must be made of compatible materials, considering temperature ratings and corrosion resistance. For example, a carbon steel valve with a stainless steel flange may cause galvanic corrosion.
• Facing: The flange facing (e.g., flat face, raised face, ring joint) must match the valve’s facing. A raised-face valve cannot be bolted to a flat-face flange without proper gasketing.
• Bore and end preparation: For welding-end valves, the bore diameter and bevel preparation must match the mating pipe or fitting. For threaded-end valves, thread type and size must align.

Procurement Checks: What to Verify Before Ordering

When procuring valves and flanges, include the following checks in your RFQ and purchase order:

1. Specify the exact standards and editions – State the edition of ASME B16.34 and ASME B16.5 you require (e.g., 2025 edition). Do not assume the manufacturer will use the latest edition.
2. Define the pressure class and size – Clearly state the NPS and class for both valve and flange. For example, “NPS 6, Class 300” for both.
3. Confirm material and material group – Specify the material grade (e.g., ASTM A105 for carbon steel flanges) and ensure the valve body material is compatible.
4. Specify facing and finish – Indicate the flange facing (RF, FF, RTJ) and surface finish (e.g., 125-250 µin Ra for raised face).
5. For welding-end valves, specify the end preparation – Provide the bevel type and dimensions per ASME B16.25 or other applicable standards.
6. Request pressure-temperature ratings – Ask for the pressure-temperature rating table for the specific material and class to verify suitability for your operating conditions.
7. Include inspection and testing requirements – Specify any required NDE (e.g., radiography, ultrasonic), hydrostatic testing, and marking per the standards.

RFQ Inputs: What to Include in Your Inquiry

To get accurate quotes, provide the following in your RFQ:

• Valve type (gate, globe, check, etc.) and end connection (flanged, threaded, welding)
• Valve size and pressure class
• Body and trim materials
• Flange standard and edition (e.g., ASME B16.5-2025)
• Flange facing and finish
• Gasket type and material (if specified)
• Bolting specification (e.g., ASTM A193 B7 studs with A194 2H nuts)
• Any special requirements (e.g., NACE MR0175, fire-safe)
• Required documentation (e.g., MTC per EN 10204 3.1 or 3.2)

Inspection and Documentation Points

During inspection, verify the following:

• Dimensional checks: Measure flange bolt circle, bore, and facing dimensions against ASME B16.5 tables.
• Marking: Check that both valve and flange are marked with the manufacturer’s name, size, class, material, and standard reference.
• Material certificates: Review mill test certificates to confirm material grade and heat treatment.
• Pressure testing: Witness hydrostatic tests if required by your specification.
• Visual inspection: Look for surface defects, weld quality (for welding-end valves), and proper facing finish.

Common Risks and How to Avoid Them

• Mismatched pressure classes: Always cross-check the class on both components.
• Incorrect facing: A raised-face valve with a flat-face flange will leak. Specify facing clearly.
• Material incompatibility: Use a material selection guide to avoid galvanic corrosion.
• Bore mismatch: For welding-end valves, ensure the bore matches the pipe schedule.
• Using outdated editions: Always specify the edition you require, as standards are periodically updated.

Related Resources

For more information on flanges and fittings, see our forged flanges and nonstandard forgings and pipe accessories pages.

Sources

• https://www.asme.org/codes-standards/find-codes-standards/b16-34-valves-flanged-threaded-welding-end
• https://www.asme.org/codes-standards/find-codes-standards/b16-5-pipe-flanges-flanged-fittings-nps-1-2-nps-24-metric-inch-standard