ASME B16.47 Series B

Covers — large diameter compact steel flanges:

• Sizes from NPS 26 through NPS 60.
• Pressure classes: 75, 150, 300, 400, 600, 900.
• Series B geometry (thinner flanges, more numerous but smaller bolts).

Does NOT cover (exclusions) — the following are governed elsewhere:

• Heavy-duty Series A large flanges → ASME B16.47 Series A.

Series B achieves the same pressure ratings as Series A but through different mechanics:

• Bolt Distribution — uses a higher quantity of smaller diameter bolts to evenly distribute the gasket seating force over a thinner flange ring, preventing distortion.

Series B flanges were originally developed by the American Petroleum Institute (as API 605) to save weight and cost in refinery piping systems, which are generally well-supported and do not experience the massive external bending moments found in cross-country pipelines.

Cost and Weight Advantages

Because Series B flanges are significantly thinner and have a smaller outside diameter than Series A, they require much less raw material. This results in huge cost savings and weight reductions, particularly in stainless steel or alloy piping systems.