02 | Standard Flanges
— Standard Flanges
Piping flanges are typically made from forged materials and machined according to standard dimensions. These parts are widely used to connect process equipment and piping lines to each other.
ASME flanges are made to standards called out by ASME B16.5 or ASME B16.47 and have machined surfaces. B16.5 refers to nominal pipe sizes (NPS) from 1/2 to 24. B16.47 covers NPSs from 26 to 60. Each specification further delineates flanges into classes 150, 300, 400, 600, 900, 1500 and 2500 for B16.5. B16.47 delineates its flanges into classes 75, 150, 300, 400, 600, 900. The ANSI Standards unify the production of flanges up to 24" size for nominal pressures up to 1500 p.s.i and for nominal pressures of 2500 p.s.i up to 12" size. ANSI flanges are of various types according to the required functions, they are divided into seven groups of nominal pressures called « series » in which the nominal pressures is indicated in « pounds per square inch»(p.s.i). These groups are the series 150, 300, 400, 600, 900, 1500, 2500 p.s.i.; they correspond to PN 10, 16, 25, 40, 64, 100, 175, kh/cm2 provided by UNI and DIN standards in the limits foreseen by the connection between pressure and temperature.
Standard Flanges
ANSI designations such as ANSI 150, ANSI 300 and so on are often followed by a # (hash symbol). The ANSI number does not directly relate to a pressure rating, but to a class of flange. For example, the hash (#) or 'pound' reference; e.g. 300 pound, can be misleading in that an ANSI 300 flange is actually rated for a test pressure of 740 psi (~5100 kPa), and only within a certain working temperature range (-20 to 100 deg F.) In most cases these are not interchangeable (e.g. an ANSI flange will not mate against a JIS flange). Further many of the flanges in each standard are divided into "pressure classes", allowing flanges to be capable of taking different pressure ratings. Again these are not generally interchangeable (e.g. an ANSI 150 will not mate with an ANSI 300).
The flange faces are made to standardized dimensions and are typically "flat face", "raised face", "tongue and groove", or "ring joint" styles, although other obscure styles are possible. Flange designs are available as "welding neck", "slip-on", "boss", "lap joint", "socket weld", "threaded", and also "blind".
— 1. Slip On Flanges (SORF) and (SOFF)
Slip-on flanges (SO) are one of the most common type of piping flanges, recommended for their use in quick assembly and saving in cost applications. These are type of flanges that slide over the end of pipes and then welded in place. A Slip-On Flange is bored slightly larger than the outer Diameter of the matching pipe and there is no need to specify the pipe schedule when using slip-on flanges due to the fact that its inside diameter is determined by the outside diameter of the pipe. This outside diameter of the pipe does not change for the different schedules.
The pipe slips into the flange prior to welding both inside and outside to prevent leaks. These are easily fitted and welded into different pipes. Welding reduces fabrication costs of these pipes. They are used for lower pressure applications and not generally recommended as compared to other types of flanges. ASME B16.5 Code limits their usage in the 1500#-2500# (lbs.) weight classes. These are available in wide variety of sizes and applications.
  • One size fits all pipe schedules.
  • Fabricators can more easily cut pipe to length for slip-on flanges.
  • The smaller thickness of this flange allows for easier alignment of bolting holes.
  • They are generally not preferred for high pressure temperature environments.

  • Advantages:
  • Low cost installation
  • Less time needed to spent on ensuring the accuracy of the cut pipe
  • They are somewhat easier to align
  • The slip-on flanges have low hub because the pipe slips into the flange before welding
  • The flange is welded both inside and outside to provide sufficient strength
  • inspection cover. It is sometimes referred to as a blanking flange.
  • fabricated applications.
  • ANSI B 16.5 Class 150
    ANSI B 16.5 Class 300
    ANSI B 16.5 Class 600
    ANSI B 16.5 Class 900
    ANSI B 16.5 Class 1500

    — 2. Weld Neck Flanges
    Welding Neck Flanges (WN), used on head coupling of pipes, are a very common type of pipe flanges used in various industrial applications. They have a tapered hub and are often used for high pressure applications. These flanges are designed to be joined to a piping system by circumferentially butt welding at its neck which means that the integrity of the butt welded area can be easily examined by radiography. The bores of both pipe and flange match, which reduces turbulence and erosion inside the pipeline. It is relatively expensive because of its neck, but is preferred for high stress applications. The neck, or hub, transmits stresses to the pipe, reducing stress concentrations at the base of the flange. The gradual transition of thickness from the base of the hub to the wall thickness at the butt weld provides important reinforcement of the flange.The bore of the flange matches the bore of the pipe, reducing turbulence and erosion. The various types of weld neck flanges are:
  • Weld Neck Flat Face Flanges
  • Raised Face Weld Neck Flanges

  • Key Features:
  • This is the most common type of high pressure pipe flange.
  • They are distinguished from other types of pipe flanges by their long tapered hub and gentle transition of thickness in the region of the butt weld joining them to the pipe.
  • The long tapered hub provides an important reinforcement of the weld neck flange proper in terms of strength and resistance to dishing.

  • Uses of weld neck flanges:
  • The weld neck flange is very resistant to dishing and has a very sturdy connection because it has the pipe along with the tapered hub.
  • The flanges are ideal for extreme fluctuations of temperature.
  • They are ideal in environments where there may be a lot of bending and handling of the flanges.
  • Preferred in an environment with extreme temperature conditions.
  • This type of flange is preferred for every severe service condition—resulting from high pressure or from sub-zero or elevated temperature.
  • They are used in situations where loading conditions are substantially constant or fluctuate between wide limits.
  • This is probably the best welding flange available because of its high, heavy neck.
  • Highly recommended wherever a sound welded joint connection is needed.

  • ANSI B 16.5 Class 150
    ANSI B 16.5 Class 300
    ANSI B 16.5 Class 600
    ANSI B 16.5 Class 900
    ANSI B 16.5 Class 1500
    ANSI B 16.5 Class 2500
    — 3. Long welding neck flanges
    These are essentially welding neck flanges but with a cylindrical neck and are much longer than normal flanges. They are used every time it is necessary to branch out pipes from a tank or pressure vessel. The greater length of the neck makes the welding to the casing much easier. Also the dismountable joint between tube and tank facilitates installation and removal of the equipment. The greater thickness of the welding edge makes the effects of the shrinkage after welding less remarkable on the flange of a much smaller bulk than that of the tank.
    — 4. Threaded (Screwed) Flanges
    These flanges are referred to as either threaded or screwed, are similar to a slip-on flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its application to relatively low pressure piping systems. Threaded Flanges are unsuited for conditions involving temperature or bending stresses of any magnitude, particularly under cyclic conditions, where leakage through the threads may occur in relatively few cycles of heating or stress; seal welding is sometimes employed to overcome this, but this is not considered a satisfactory method of increasing its pressure applications. This type generally is used for special requirements; their advantage is the possibility to work under considerably high temperatures and pressures, avoiding the welding joint on assembly which requires a difficult heat treatment with alloy steel. They are not recommended when there is the possibility of bending stress on the pipe because, in a short time, losses on the threads would result.
    The various types of threaded flanges are as follows:
  • Plain Threaded Flanges- Female Threaded Flanges
  • Male Threaded Flanges
  • ANSI B 16.5 Class 150
    ANSI B 16.5 Class 300
    ANSI B 16.5 Class 600
    ANSI B 16.5 Class 900
    ANSI B 16.5 Class 1500
    ANSI B 16.5 Class 2500
    — 5. Reducing Flanges
    Reducing flanges are designed for use in changing diameters in a piping system. On the other hand, to connect two sized pipes, the appropriate reducing flange is inserted between the two and bolted into place. A reducing flange comprises a flange with one specified diameter having a bore of a different and smaller, diameter. Except for the bore and hub dimensions, the reducing flange will have dimensions of the larger pipe size. These flanges are used at the outlet side of the expansion joint to increase the size of the flange. This is considered to be an economical method to make a transition in size. Usually they are the threaded, welding neck or socket welding type. They are recommended for high nominal pressures only; in all other cases it is advisable to weld a reducing pipe with much less high losses of force on pipe line.
    Types of Reducing Flanges:
    Reducing flanges are normally provided as one of the following three types:
  • Welding Neck
  • Slip-On
  • Threaded etc.

  • Uses of Reducing Flanges:
  • Reducing flanges are used in pipe-to-pipe connections.
  • Reducing flanges are a little easier to bolt up than non-reducing flanges.
  • They provide the most perfect solution when you need to connect different size flanges.
  • These flanges are available in all types and pressures.
  • Reducing flanges are fixed by welding, gluing or clamping flanges of equal dimensions provided with different connecting pieces.
  • They offer the simplest and least expensive method of mating two different sized flanges.

  • ANSI B 16.5 Class 150
    ANSI B 16.5 Class 300
    ANSI B 16.5 Class 600
    ANSI B 16.5 Class 900
    ANSI B 16.5 Class 1500
    ANSI B 16.5 Class 2500
    — 6. Blind Flanges
    Blind flanges, generally used to blank off one of a flanged pipelines, a valve, a pump or the opening of a pressure vessel, they can also be used as an inspection cover and permits easy access to a line ones it has been sealed. It is sometimes referred to as a blanking flange. Owing to their form, they are not recommended if water hammers in the piping are possible. In this case it is better to stop the pipe by using welding neck flanges or slip-on flanges provided with a welded cap. The blind flange is sometimes machined to accept a pipe of the nominal Size to which reduction is being made. The reduction can be either threaded or welded. ANSI B 16.5 Class 900 ANSI B 16.5 Class 1500 ANSI B 16.5 Class 2500
    — 7. Ring Joint Flanges
    Ring Type Joint Flange is a method of ensuring leak proof flange connection at high pressures. A metal ring is compressed into a hexagonal groove on the face of the flange to make the seal. This jointing method can be employed on Weld Neck, Slip-on and Blind Flange. RTJ flanges have grooves cut into their faces which accept steel Ring Gaskets. RTJ flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or "Coining") the gasket to make Intimate Contact inside the grooves, creating a metal to metal seal. An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. For RTJ flanges that seal with ring gaskets, the raised faces of the connected and tightened flanges may contact each other. In this case the compressed gasket will not bear additional load beyond the bolt tension, vibration and movement cannot further crush the gasket and lessen the connecting tension.
    — Materials
    Materials can be supplied as per customer''s special rquirements/Dimensions/Drawings/Specification and Varous other national and international standards.
    Materials for flanges are usually under ASME designation:
    SA-105 (Specification for Carbon Steel Forgings for Piping Applications)
    SA-266 (Specification for Carbon Steel Forgings for Pressure Vessel Components)
    SA-182 (Specification for Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service).

    In addition, there are many "industry standard" flanges that in some circumstance may be used on ASME work.
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