MAKING THE CONNECTION: FLANGE FACING TYPES
Flange design is only the start when considering the ideal flange for your piping system. Face types are another characteristic that will have a major impact on the final performance and service life of your flanges.
Facing types determine both the gaskets needed to install the flange and characteristics related to the seal created.
Common face types include:
Flat Face (FF): As the name suggests, flat face flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.
Raised Face (RF): These flanges feature a small raised section around the bore with an inside bore circle gasket.
Ring Joint Face (RTJ): Used in high-pressure and high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal.
Tongue and Groove (T&G): These stainless steel blind flanges feature matching grooves and raised sections. This aids in installation as the design helps the flanges to self-align and provides a reservoir for gasket adhesive.
Male & Female (M&F): Similar to tongue and groove flanges, these flanges use a matching pair of grooves and raised sections to secure the gasket. However, unlike tongue and groove flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.
Many face types also offer one of two finishes: serrated or smooth.
Choosing between the options is important as they will determine the optimal gasket for a reliable seal.
In general, smooth faces work best with metallic gaskets while serrated faces help to create stronger seals with soft material gaskets.
Duplex alloys were originally created to counter the corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids. They are known to be Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The term “Super-Duplex” is used to denote highly alloyed, high-performance Duplex steel with a pitting resistance equivalent of >40 (based on Cr % + 3.3Mo % + 16N %).
With a high level of chromium, Duplex steel plate flange provides outstanding resistance to acids, acid chlorides, caustic solutions and other environments in the chemical/petrochemical, pulp, and paper industries.
Super Duplex contains 25% chromium, 7% nickel, 3.6% molybdenum as well as copper, tungsten, and nitrogen, they are highly alloyed steel with high PREN for use in aggressive environments.
The alloy consists of around 40-50 percent ferrite in the annealed condition. The super duplex microstructure has the high strength of the ferritic grades in spite of retaining the corrosion resistance of the austenitic grades. It is common to see Super Duplex Steel being used as a practical solution to chloride-induced stress cracking. It also has outstanding resistance against sulfide-stress corrosion cracking in sour-gas environments.
Super Duplex UNS S32750 Flanges help the material withstand pitting and crevice corrosion. These duplex steel blind flanges are also resistant to chloride stress corrosion cracking, to erosion-corrosion, to corrosion fatigue, to general corrosion in acids. They have good weldability and very high mechanical strength.