Scope and class comparison

The current ASME product pages identify B16.5-2025 and B16.47-2025. A project may contractually require another edition, so the purchase order and design documents remain controlling.

What Series A and Series B mean

Series A and Series B provide different dimensional patterns for large-diameter flanges. Differences can include flange outside diameter, thickness, bolt circle, bolt quantity and bolt size. A flange can have the same NPS and class yet fail to mate because the series is different.

Series A is generally associated with a more robust, heavier pattern, while Series B can be more compact. That broad description should never replace the dimension table. Confirm the mating equipment nozzle, valve or existing flange by drawing, standard edition and measured bolt pattern before ordering a replacement.

Material and ratings are separate decisions

The dimensional standard does not turn “alloy steel” into a complete material specification. State ASTM A182 plus the exact grade for forged alloy or stainless flanges, or the other approved material specification. Pressure-temperature ratings depend on the standard’s material grouping and adopted edition.

Facing also remains a separate requirement. RF and RTJ joints use different gasket concepts and machining. Bore, weld end and hub details must suit the connecting pipe. For large custom connections, dimensional verification and an approved drawing are particularly valuable.

Purchase-order wording that prevents mismatch

• ASME B16.5 or ASME B16.47 and the required edition
• NPS, class and flange type
• B16.47 Series A or Series B where applicable
• RF, RTJ or other specified facing and finish
• Material specification, grade and heat-treatment condition
• Bore, pipe schedule and weld-end detail
• Bolting, gasket and mating-flange reference when compatibility is critical
• Dimensional report, NDE, MTC and marking requirements

For brownfield replacements, include a site measurement sheet or approved equipment drawing. Standard shorthand alone may not capture legacy or proprietary connections.