Series A Class 900 Flanges

Series A Class 900 flanges represent the highest standard pressure class available for large-diameter flanges under B16.47. The available size range at Class 900 is typically more limited than lower classes, often covering NPS 26 through NPS 36, as the practical and economic constraints of manufacturing extremely thick, large-diameter forgings become significant.

At Class 900, the flange body thickness, bolt size, and bolt count reach their maximum values within the Series A specification. These flanges are reserved for the most critical high-pressure applications in the petroleum, petrochemical, and power industries, including high-pressure separator vessels, reactor feed/effluent systems, and supercritical steam headers.

Fabrication of Class 900 large-diameter flanges requires advanced forging capabilities with strict quality controls. Full volumetric NDE, hardness testing, and impact testing are standard requirements. Material traceability per ASME Section II is mandatory, and positive material identification is routinely performed at the point of installation.