Flat face (FF) flanges have a gasket surface in the same plane as the bolting face, with no raised area. They are used with a full-face gasket that covers the whole flange face inside and outside the bolt holes, spreading the bolt load evenly. This is essential when a steel flange is bolted to a brittle or flexible flange such as cast iron, ductile iron or fibreglass, which would crack or distort against a raised face.
Raaj Fittings manufactures FF flanges to ASME B16.5, EN 1092-1 (facing type A), DIN, BS and JIS standards at our two plants in India, in carbon and stainless steel and other grades.
FF flanges use full-face gaskets, cut with bolt holes, in rubber, compressed fibre or PTFE. The bolt load is spread over a large gasket area, so FF joints are suited to low and moderate pressures. Bolting should be tightened evenly in a cross pattern to avoid stressing a brittle mating flange.
A flat-face flange should never be bolted to a raised-face flange where the mating flange is cast iron or plastic: the raised face acts as a fulcrum and the brittle flange can crack when the bolts are tightened. Where an RF steel flange must meet an FF cast-iron flange, specifications normally require the steel flange to be supplied flat-faced.
Every FF flange is made from PMI-verified material, dimensionally inspected against the ordered standard and marked with material, size, rating and heat number. Orders are supplied with EN 10204 3.1 certificates; EN 10204 3.2 certification and inspection by the buyer's nominated third-party agency are available on request.
To mate with cast iron, ductile iron or plastic flanges, which would crack or distort against a raised face, and in low-pressure systems using full-face gaskets.
A full-face gasket that covers the whole flange face, with holes for the bolts, typically in rubber, compressed fibre or PTFE.
Not when the FF flange is cast iron or plastic. Use flat face flanges on both sides so the bolt load does not bend the brittle flange.
Yes, FF flanges are available in stainless steel, carbon steel and other grades, to ASME, EN, DIN, BS and JIS standards.