Flange Dimensions and Tolerance Specifications

Product details description

　　In piping systems, a flange is the connector that joins pipes to valves, pumps, or walls. Precision in dimensions and tolerances is not just a quality metric; it is a safety requirement to prevent leaks and catastrophic failures under pressure.

　　Key Standards

　　The two dominant standards are ASME B16.5 (US/Imperial) and EN 1092-1 (European/Metric). A "Class 150" flange in B16.5 is not interchangeable with a "PN10" flange in EN standards, even if the pipe size matches.

　　Critical Dimensions

　　Bolt Circle Diameter (BCD): The circle formed by the center of the bolt holes. If this is off by even 1mm, bolts won't line up, causing uneven gasket compression and leaks.

　　Number of Holes: Must match the mating flange exactly.

　　Bore Size: The inner diameter must match the pipe's outer diameter (OD) to ensure smooth flow (full bore) or specific flow rates (reduced bore).

　　Raised Face (RF): The height of the sealing surface. Standard RF is 1/16" (1.6mm). Ring Joint (RTJ) flanges have grooves for metal gaskets.

　　Tolerance Classes

　　Diameter Tolerance: For a 12-inch flange, the tolerance is usually ±0.25mm to ±0.5mm.

　　Squareness: The flange face must be perfectly 90 degrees to the bore. If tilted, the gasket won't seal evenly when the bolts are tightened.

　　Surface Finish: The sealing face usually requires a roughness average (Ra) of 125μin to 250μin. Too smooth, and the gasket slips; too rough, and it cuts into the gasket.

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