ANSI/ASME B16.5
Flange Dimensions

Match three things: the nominal pipe size (NPS), the pressure and temperature rating your system requires (which sets the class, such as Class 150 or Class 300), and the standard for that size. ANSI/ASME B16.5 covers sizes up to 24 inch, ANSI/ASME B16.47 covers 26 inch and larger, and AWWA C207/C228 covers water service. Then confirm the bolt circle and drilling match the mating flange. API International stocks domestic (AIS) and imported flanges and can help you confirm the right specification.

ANSI/ASME B16.5 covers flanges and flanged fittings from NPS ½ inch through 24 inch in seven pressure classes: 150, 300, 400, 600, 900, 1500, and 2500. The class sets the pressure and temperature rating, and each class has its own dimensions, bolt circle, and drilling. Larger sizes, 26 inch and up, fall under ANSI/ASME B16.47 instead.

The bolt circle, also called the bolt hole circle (B.H.C.) or bolt circle diameter, is the diameter of the imaginary circle that passes through the centers of all the bolt holes. It sets where the bolts sit and must match the mating flange exactly, even when two flanges share the same outside diameter. Every dimension table lists the bolt circle along with the number and size of the bolt holes.

No. The dimensions (outside diameter, bolt circle, bore, thickness and drilling) are set by the governing standard, ANSI/ASME or AWWA, and stay the same whether the flange is carbon steel, stainless steel, galvanized, epoxy coated or painted. Material and finish affect corrosion resistance, pressure and temperature limits, and weight, but not the dimensional layout.

The class is a pressure and temperature rating. At a given temperature, a Class 300 flange is rated for higher pressure than a Class 150 flange. Class 300 is also physically heavier, with a larger bolt circle and more (and larger) bolts. Select the class that matches the maximum pressure and temperature of your piping system; the two classes are not interchangeable.

ANSI/ASME B16.5 covers weld neck, slip-on, blind, threaded, socket weld, and lap joint flanges. For a given size and class, every type shares the same outside diameter, bolt circle, and drilling, so they bolt to the same mating flange. What changes between types is the hub and the bore.

Yes. API International machines custom bores, facings (raised face, flat face and ring type joint) and nonstandard sizes in house, including flanges outside standard class and size combinations. Send us your specification or drawing for a quote.