Above 24 Inches: ASME B16.47 and MSS SP-44

ASME B16.5 covers flanges up to 24 inches. Above that, ASME B16.47 takes over, and it contains two different series.

Series A and Series B

The two series do not bolt together. Even at the same nominal size and class, bolt circle and bolt count differ. One of the most expensive field mistakes is ordering without stating the series and receiving the wrong one.

Where MSS SP-44 sits

MSS SP-44 is a separate standard for pipeline flanges and is the origin of B16.47 Series A. Pipeline specifications often refer to it directly. On the material side, high strength ASTM A694 grades (F52, F60, F65, F70) compatible with API 5L pipe are used.

What to watch in large sizes

• Weight and handling. A 36" flange alone can weigh hundreds of kilograms; lifting must be planned at order stage.
• Gaskets. An inner ring on a spiral wound gasket is effectively mandatory at large diameters to stop the winding buckling inwards.
• Bolt load. Hydraulic tensioning is preferred over torque, because equal preload is critical at these sizes.
• Lead time. These sizes usually come from production rather than stock.

When ordering

State size, pressure class, series (A or B), standard (B16.47 or MSS SP-44), material grade, face type and, for weld neck, the pipe wall thickness.

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FAQ

Can Series A and Series B be bolted together?
No. Bolt circle and bolt count differ even at the same size and class.

Are MSS SP-44 and B16.47 Series A the same?
Series A originates from MSS SP-44 and the dimensions largely overlap; order to whichever the specification names.

Which materials are used in large diameter flanges?
A694 F52 to F70 on transmission lines, and A105 and alloy grades on process lines.