Series B Class 300 Flanges

Series B Class 300 flanges offer medium-pressure capability for large-diameter piping with material and weight savings compared to the Series A equivalent. The API 605 lineage of these flanges reflects a design philosophy that optimizes bolt pattern and flange thickness for the actual service loads rather than providing the additional conservatism built into MSS SP-44.

At Class 300, the difference in flange thickness between Series A and Series B becomes more pronounced. A Series B flange may be 15 to 20 percent lighter than its Series A counterpart at the same NPS and class, translating to significant cost savings on large projects with many flanged connections.

These flanges are appropriate for process piping in refineries, chemical plants, and gas processing facilities where the service conditions are well-understood and do not involve severe cyclic loading, high-vibration environments, or frequent thermal transients that would favor the additional stiffness of Series A.