End connections provide the means for installation of control valves in pipelines. Popular end connections include several types of screwed pipe threads, bolted and gasketed flanges, and welded-end connections.
Common Flange Connections
Raised-Face Flange – The raised-face flange (see Figure 32) is the most common end connection. These flanges have circular, raised faces with concentric, circular grooves for good gasket sealing and resistance to gasket blowout. The line gasket only covers the raised-face portion of the flange. As the line bolting is tightened, high stresses are produced at the perimeter of each flange; therefore, raised-face flanges are available only for strong, ductile (non-brittle) materials such as carbon steel and stainless steel.
Flat-Face Flange – The flat-face flange (see Figure 32) allows full-face contact, with the gasket clamped between the flanges. Full-face contact has the advantage of minimizing flange stresses that are caused by the force of line bolting. Flat-face flanges are common with cast iron bodies, which are brittle and would crack if raised-face flanges were used. Flat-face flanges are also common with brass and aluminum bodies, which are soft and would bend if raised-face flanges were used. Flat-face flanges are generally limited to low pressure applications.