THE BASICS OF STEEL FLANGES
Stainless steel flanges provide an easy access for cleaning, inspection or modification. They usually come in round shapes but they can also come in square and rectangular forms. The flanges are joined to each other by bolting and joined to the piping system by welding or threading and are designed to the specific pressure ratings; 150lb, 300lb, 400lb, 600lb, 900lb, 1500lb and 2500lb.
A flange can be a plate for covering or closing the end of a pipe. This is called a blind flange. Thus, flanges are considered to be internal components which are used to support mechanical parts.
Each flange material is to be considered for its application prior to ordering, this is due to the structural integrity of the application that the flange will be used on.
Currently, the most common materials for flanges are:
? ASTM A105/A266 Gr.2 (high temperature carbon steel flanges)
? ASTM A350 LF1 to LF3 (low temperature carbon steel flanges)
? ASTM A694 Gr. F42/F52/F56/F60/F65 (high yield carbon steel flanges to match API 5L linepipes)
? ASTM A182 Gr. F1/F2/F5/F9/F11 Cl.2/F12 Cl.2/F22 Cl.3/F91 (alloy steel flanges)
Stainless / Duplex Steel
? ASTM A182 F304/304L, 316/316L, 321, 347, 348 (stainless steel flanges), 904/904L
? ASTM A182 F51 (duplex flanges)/F53-F55 (superduplex flanges)
Nickel Alloys / Superalloys
? ASTM B166 UNS NO6600 (Inconel 600)
? ASTM B564 UNS N06625 (Inconel 625)
? ASTM B425 UNS-NO8800 (Incoloy 800)
? ASTM B564 UNS N08825 (Incoloy 825)
? ASTM B160 UNS N0200 (Nickel 200)
? ASTM B564 UNS N04400 (Monel 400)
? ASTM B564 UNS N10276 (Hastelloy C-276)
? ASTM B381 Gr.2 (Titanium)
In industry, flanges, including stainless steel flate flanges, stainless steel slip on flanges, and stainless steel weld neck flanges, form a vital connecting link for piping, valves and other equipment. They provide an easy point of access for cleaning, inspection, modification, and for necessary repairs. A flanged joint provides a strong seal in a closed system, and is made by bolting together a gasket flanked by two flanges.
In heavy industry, these flanges need to be especially resilient or they can prove to be the weak point in a system. It is important therefore, to ensure that the flanges you are choosing are up to the task.
Why are stainless steel flanges preferred for industrial use?
In all metal applications, corrosion is a constant consideration. Rust, chemicals and other environmental factors all take their toll on metals. Therefore, the choice of flange would need to be resistant to these factors. Stainless steel outperforms other metal flanges – including carbon steel – due to its high resistance to corrosion.
Stainless steel is incredibly strong and durable, capable of withstanding immense pressures. By comparison, aluminium may be a cheaper option but it is softer and not as reliable under heavy stress.
Any system or piece of equipment is only as strong as its weakest part. Joins and welds are traditionally a weak point, so it would be wise to make sure that your choice of metal is correct for the application.
Depending its use, a flange may need to withstand high very temperatures. The correct grade of stainless steel flange would ensure that there is no warping or deformation which would compromise the system.
Cheaper, lower grade metal flanges may be fine for certain applications, but if you want your system or equipment to work at maximum capacity, then you should consider spending a little more on stainless steel flanges.
WHAT ARE PIPE FLANGES AND HOW DO THEY WORK?
Offering a reliable way to connect pipe systems with the various equipment, valves, and other components of virtually any processing system, flanges are the second most used joining method after welding.
Using flanges adds flexibility when maintaining piping systems by allowing for easier disassembly and improved access to system components.
A typical flanged connection is comprised of three parts:
In most cases, there are specific gasket and bolting materials made from the same, or approved materials as the piping components you wish to connect. Stainless Steel flanges are some of the most common, and mostly stainless steel threaded flanges. However, flanges are available in a wide range of materials so matching them with your needs is essential.
Other common flange materials include Monel, Inconel, Chrome Moly, and many others depending on the application.
The best option for your needs will depend on both the system in which you intend to use the flange and your specific requirements.
COMMON FLANGE TYPES AND CHARACTERISTICS
Flanges are not a one-type-fits-all sort of solution. Sizing aside, matching the ideal flange design to your piping system and intended usage will help to ensure reliable operation, a long service life, and optimal pricing.
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.
Benefits of Super Duplex Flanges
High resistance to pitting, crevice corrosion.
High resistance to stress corrosion cracking, corrosion fatigue, and erosion,
Excellent resistance to chloride stress- corrosion cracking
High thermal conductivity
Good sulfide stress corrosion resistance,
Low thermal expansion and higher heat conductivity than austenitic steels,
Good workability and weldability,
High energy absorption.
Applications of Super Duplex Steel Flanges
Heat exchangers, tubes and pipes for production and handling of gas and oil,
Heat exchangers and pipes in desalination plants,
Mechanical and structural components,
Power industry FGD systems,
Pipes handling solutions containing chlorides,
Utility and industrial systems, rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized,
Cargo tanks, vessels, piping and welding consumables for chemical tankers.
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