Glossary term
Flange
A projecting rim, collar, plate, or ring used to connect, stiffen, locate, seal, or transmit load between components.
Definition
deviceA projecting rim, collar, plate, or ring used to connect, stiffen, locate, seal, or transmit load between components.
A flange is a mechanical interface. Its design may involve bolt preload, gasket compression, weld detail, pressure containment, bending stiffness, alignment, fatigue, corrosion, thermal expansion, and inspection access.
A flange is a projecting feature used to create a mechanical interface. It may connect pipe sections, mount a motor, stiffen a shell, locate a bearing housing, attach a valve, support a wheel, or provide a sealing face. The details depend on function: connection, alignment, pressure containment, load transfer, or manufacturability.
Engineering role
Flanges make assemblies separable, inspectable, alignable, and serviceable. In piping and pressure equipment, a bolted flange joint must contain internal pressure while maintaining gasket compression. In machines, a mounting flange must transfer loads without excessive deflection, fretting, or misalignment. In sheet metal and structures, flanges add stiffness and local stability.
Design considerations
Important variables include flange thickness, bolt circle, bolt size, gasket type, facing finish, weld detail, hub geometry, material, corrosion allowance, pressure class, temperature, and external loads. The flange is rarely designed alone; bolt preload, gasket relaxation, pipe loads, thermal expansion, and installation practice all affect performance.
Manufacturing
Flanges may be forged, cast, machined, welded, formed, or cut from plate. Manufacturing route affects grain flow, defects, residual stress, surface finish, and dimensional tolerance. Welded flanges require attention to weld quality, heat-affected zones, distortion, inspection, and fatigue-sensitive details.
Failure modes
Common failure modes include leakage, bolt relaxation, gasket blowout, flange rotation, cracking at weld toes, corrosion under insulation, fretting at mounting faces, and fatigue at stress concentrations. In rotating equipment, runout and face flatness can be as important as static strength.
Common mistakes
Common mistakes include checking only nominal pressure rating while ignoring external loads, thermal cycles, gasket compatibility, and bolt preload. Another error is treating a flange as a rigid boundary in analysis when its flexibility strongly affects sealing, alignment, or local stress.