Introduction

flange is an external or internal ridge, or rim (lip), for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or for a flange of a rail car or tram wheel. Thus flanged wheels are wheels with a flange on one side to keep the wheels from running off the rails. The term “flange” is also used for a kind of tool used to form flanges.  The type of flange to be used for a piping application depends, mainly, on the required strength for the flanged joint. Flanges are used, alternatively to welded connections, to facilitate maintenance operations – Pipes with flanges can be assembled and disassembled easily. The flange is the second most used joining method after welding. A flanged joint is composed of three separate and independent although interrelated components; the flanges, the gaskets, and the bolting; which are assembled by yet another influence, the fitter.

International Standards

Design According to EN Type According to DIN
Weld Neck Flange Type 11 DIN 2627 – DIN 2638
Blind Flange Type 05 DIN 2527
Threaded Flange Type 12 DIN 2558, DIN 2565 – DIN 2569
Flat Flange Type 01 DIN 2573, DIN 2576
Lapped Flange Type 02 & Type 04 DIN 2641, DIN 2642, DIN 2655, DIN 2656

Similar to ASME flanges, EN1092-1 steel and stainless flanges, have several different versions of raised or none raised faces. According to the European form the seals are indicated by different form:

Form: types of Contact Faces DIN EN 1092-1
Without Raised Face Form A
Raised Face (Rz = 160 Mechanical Turned) Form B1
Raised Face ( Rz = 40 Mechanical Turned) Form B1
Raised Face (Rz = 16 Mechanical Turned) Form B2
Tongue According to DIN2512 Form C
Groove According to DIN 2512 Form D
Male According to DIN 2513 Form E
Female According to DIN 2513 Form F
Female According to DIN 2514 Form G
Male According to DIN 2514 Form H

Types Of Flanges

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1. Threaded Flanges:- 

    • Threaded flanges can be fitted to pipes of various sizes without welding and this is one chief benefit for which these flanges are highly demanded.
    • They can be used in extremely high pressure applications, particularly at or near atmospheric temperature, where the necessary post weld heat treatment is not possible.
    • They are ideal for small diameter piping applications.
    • They are economical and time saving devices.
    • These threaded flanges are normally designed for non-cyclic applications.
    • The flanges are suitable to be used in applications where welding is hazardous.
    • They can be used in highly explosive areas.
    • Threaded flanges are widely demanded as pipe flanges i.e called as threaded pipe flanges used in different industrial applications.
    • Threaded Flanges are also known as screwed flange, and it is having a thread inside the flange bore which fits on the pipe with matching male thread on the pipe.
    • Threaded (Screwed) flange is similar to the Slip-On flange, but the bore is threaded.
    • The various types of threaded flanges are as follows:
      • Plain Threaded Flanges
      • Female Threaded Flanges
      • Male Threaded Flanges

2. Socket-Weld Flanges

    • The socket weld flange, abbreviated as SWF, is similar to a slip-on flange, except only one fillet weld is made to the flange and pipe.
    • Socket-Weld Flanges has a female socket in which pipe is fitted. Fillet welding is done from outside on the pipe.
    • The socket welding flange is similar to a slip-on flange except it has a bore and a counterbore dimension.
    • The pipe need not be beveled for weld preparation. Temporary tack welding is no needed for alignment, because in principle the fitting ensures proper alignment.
    • The weld metal can not penetrate into the bore of the pipe.
    • They can be used in place of threaded fittings, so the risk of leakage is much smaller. Radiography is not practical on the fillet weld; therefore correct fitting and welding is crucial. The fillet weld may be inspected by surface examination, magnetic particle (MP), or liquid penetrant (PT) examination methods.
    • Construction costs are lower than with butt-welded joints due to the lack of exacting fit-up requirements and elimination of special machining for butt weld end preparation.
    • Pipe is welded to socket weld flanges by inserting the pipe into the socket and backing the piping out between 1/16” and 1/8”. This is to prevent the expanding pipe on the inner side of the weld from expanding when headed and cracking the weld on the fitting.

3. Welding Neck Flange

    • A weld neck flange (also known as a high-hub flange and tapered hub flange) consists of a circular fitting with a protruding rim around the circumference.
    • There are two designs. The regular type is used with pipes. The long type is unsuitable for pipes and is used in process plant.
    • Generally machined from a forging, these flanges are typically butt welded to a pipe. The rim has a series of drilled holes that permit the flange to be affixed to another flange with bolts.
    • Such flanges are suitable for use in hostile environments that have extremes of temperature, pressure or other sources of stress.
    • The resilience of this type of flange is achieved by sharing the environmental stress with the pipe with which it is welded.
    • This type of flange has been used successfully at pressures up to 5,000 psi.
    • Weld neck flanges are Bulky & costly with respect to other types of flange.

4. Slip On Flange

    • Slip-On flange has a hole with matching outside diameter of pipe from which pipe can pass.
    • Slip on Flange is essentially a ring that is placed over the pipe end, with the flange face extending from the end of the pipe by enough distance to apply a weld bead on the inside diameter. The OD of slip on flange is also welded on the back side of the flange.
    •  Slip-On Flange is suitable for low pressure and temperature application.
    • This type of flange is available in large size also to connect big bore piping with storage tank nozzles.
    • Socket Weld Flanges are used for small-size and high-pressure piping that do not transfer highly corrosive fluids. This due to the fact that these flange types are subject to corrosion in the gap area between the end of the pipe and the shoulder of the socket.

5. Lap Joint Flange

    • Lap joint flanges resemble, in shape, slip-on flanges except for the radius at the crossing of the flange face and the bore to accommodate the flanged portion of the stub end.
    • Reduces the overall cost of the pipeline’s flanged joints, as the use of higher grade materials is minimized.
    • Bolting operations are simplified, as the lap joint flange can be rotated around the pipe to help with bolts alignment.
    • Lap flange is used where frequent dismantling is required, and space is constrained.
    • It is primarily used in carbon or low alloy steel piping systems.

6. Blind Flange

    • A blind flange is a solid disk used to block off a pipeline or to create a stop.
    • The blind flange is a blank disc with bolt hole.
    • These types of flanges are used with another type of flange to isolate the piping system or to terminate the piping as an end.
    • Blind flanges are also used as a manhole cover in the vessel.
    • Blind flanges are commonly produced and stocked in several different materials.
    • They are often called Blank Flanges.
    • Blind flanges are commonly used in petrochemical, pipe engineering, public services and water works.
    • Without a blind flange, it would be next to impossible to repair or perform ongoing maintenance to a pipeline unless the flow was shut off at a earlier valve, which could affect miles of pipeline.
    • It is maybe interesting to observe that, while this flanges type is easier to manufacture, they are sold at a premium average cost per kilogram compared to the other flange types.

Special Types of Flange:

Types of Flanges

Types of Flanges

  1. NipoFlange:- A Nipoflange is used for branch pipelines at 90 degrees and is a product manufactured by combining a welding neck flange with a forged Nipolet.
  2. WeldoFlange:-A Weldoflange is conceptually similar to a Nipoflange, as that they are a combination of a weld neck flange and a branch fitting connection (a Weldolet in this case). Weldoflanges are made out of a single piece of solid forged steel, not by welding separate parts together.
  3. ElbowFlange and LatroFlange:- Other less common types of flange Olets is the so-called Elboflange (a combination of a flange and an Elbolet) and “Latroflange” (combination of a flange with a Latrolet). Elboflanges are used to branch a pipeline at 45 degrees.
  4. Swivel Flange:- The Swivel Flanges permits 360° rotation of an outer ring around a hub, to allow easy alignment of bolt holes when attaching to a mating standard flange. For subsea applications, this capability is important when only a single diver is available to align and make up the flange connection. Swivel ring flanges facilitate the alignment of the bolt holes between the two mating flanges, a feature that is helpful in many circumstances, such as the installation of large diameter pipelines, subsea and offshore pipelines, pipe works in shallow waters and similar environments.Swivel flanges suit oil, gas, hydrocarbons, water, chemical and other demanding fluids in petrochemical and water management applications.
  5. Expanding Flange:- Expander Flanges is a Welding Neck pipe flange where the nominal size of the non-flanged end is larger than the nominal size of the flanged end. They can be used to change the size of a pipe run. These are usually used to increase the line size to the first or second larger size. This is an alternative to using a separate reducer and weld neck flange combination. The expander flange can be used to connect pipe to pumps, compressors and Valves.
  6. Reducing Flange:- Reducing flanges are specified by giving firstly the size from which the reduction is made, followed by the reduced size. They are available in all pressure classes and provide a good alternative to connecting two different sizes of pipe. This type of flange should not be used if an abrupt transition would create unwanted turbulence, such as at a pump. Reducing flanges are normally provided as one of three types:
    • Reducing Welding Neck flange
    • Reducing Slip-On flange
    • Reducing Threaded flange

Other Flange Classification

The shape is the most obvious way to classify the different type of flanges. However, other ways to classify flanges exist and they are:

Flange Face Type

  • Flat Face (FF)
  • Raised Face (RF)
  • Ring Joint (RTJ)
  • Tongue and groove (T&G)
  • And Male and Female type

Flange Dimensions

  • Pipe Size – Pipe flanges also have a corresponding pipe size, generally according to accepted standards.
  • Outside Diameter of Flange (OD) – this is measured from outer edge to opposing outer edge.
  • Pitch Circle Diameter (PCD) – this is a diameter that measures from the center of bolt hole to opposing bolt hole.
  • Flange Thickness – this measures only the thickness of the attaching outer rim, and does not include the part of the flange that holds the pipe.
  • Nominal Size
  • Pressure Ratings

Flange Finish

  • Smooth
  • Serrated
  • Stock

Types of Connection

  1. Bolted Flange connections:- A bolted flange connection is a complex combination of many factors (Flange, Bolts, Gaskets, Process, Temperature, Pressure, Medium). All these various elements are interrelated and depend upon one another to achieve a successful result. The reliability of the flanged joint depends critically upon competent control of the joint making process.

Pressure Temperature Ratings

  • Higher the rating, heavier the flange and can withstand higher pressure and temperature.
  • When the temperature goes up, the pressure goes down, and vice versa.
  • Flanges are classified as per their pressure-temperature ratings which are designated as 150#, 300#, 400#, 600#, 900#, 1500# and 2500#.
  • Large diameter flanges i.e. 24” to 60” are available up to 900# class.

Material Types

  • Carbon Steel: – ASTM A105, ASTM A350 LF1 /LF2 /LF3, ASTM A181, ASTM A694 F42, F52, F60, F655
  • Alloy Steel: – ASTM A182 F1 /F2 /F5 /F5a /F7 /F9 /F11 /F12 /F22/ F91
  • Stainless Steel: – ASTM A182 F6 /F304 /F304L /F316 /F316L/ F321 /F347 /F348, ASTM A182 F51 (duplex flanges) /F53-F55 (superduplex flanges)
  • Or Combination of Exotic materials (Stub) and other backing materials:-
    • 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)
    • Titanium:- ASTM B381 Gr.2 (Titanium)
    • Aluminium
    • Copper
    • Polypropylene, etc.
  • List of materials used to manufacture flanges is covered in ASME B16.5 & B16.47 :-
    • ASME B16.5 -Pipe Flanges and Flanged Fittings NPS ½” to 24”
    • ASME B16.47 -Large Diameter Steel Flanges NPS 26” to 60”

Flange Inspection

  • Outer & Inner Diameter of body
  • Bolt Circle & Bolt hole Diameter
  • Hub Diameter & thickness of weld end
  • Length of the Hub
  • Straightness and alignment of the bolt hole

Marking

  • Manufacturer logo
  • ASTM material code
  • Material Grade
  • Service rating (Pressure-temperature Class))
  • Size
  • Thickness (Schedule)
  • Heat No
  • Special marking if any QT (Quenched and tempered) or W (Repair by welding)

ASME, ANSI and MSS Specifications

The standards govern the dimensions and tolerances to which fitting are manufactured:

  • ASTM A.182 – Forged or Rolled Alloy Steel Pipe Flanges & Fittings for high temperature service
  • ANSI B. 16.5 – Steel Pipe Flanges and Flanged Fittings (½ inch to 24 inch nominal diameter)
  • MSS SP.6 – Flange Facings
  • MSS SP.25 – Marking of flanges
  • MSS SP.39 – Bolts and Nuts for Flanges
  • MSS SP.44 – Large Diameter Pipeline Flanges. (Over 24 inch dia)
  • API-605 – Large Diameter Flanges for petroleum Usage. (Over 24 inch dia)
  • The following are not flange specifications but they influence the manufacture of forged steel flange:  • ANSI B. 31.10 – Code for Pressure Piping
      • ANSI B. 31.3 – Petroleum Refinery Piping
      • ANSI B. 31.4 – Oil Transportation Piping
      • ANSI B. 31.5 – Refrigeration Piping Systems
      • ANSI B. 31.7 – Nuclear Power Piping
      • ANSI B. 31.8 – Gas Transmission and Distribution Piping systems
      • ANSI B. 36.10 – Standard for Wrought Steel pipe
      • ANSI B. 36.19 – Standard for Stainless Steel Pipe
      • ANSI B. 16.10 – Valve Dimensions Face & End
      • ANSI B. 16.11 – Forged Fittings Socket Weld & Threaded

Advantages of Flanges

  • A new line can contain multiple pipe spools and can be manufactured in a workshop.
  • This pipe spools can be assembled in the plant without the need to be welded.
  • NDO (X-ray, Hydro test etc.) in the plant is not necessary, because this has been done in the workshop.
  • Blasting and painting in the plant is not necessary, because even this has been done in a workshop
    (only paint damages during installation should be repaired).

Disadvantages of Flanges

  1. Each flange connection can leak (some people claim that a flange connection is never 100 percent leak proof). Special controls are required in the selection and application of all these elements to attain a joint, which has acceptable leak tightness. However, it is not advisable to used flange connection in underground piping when it supposed to be buried. The flange is also the most common source of leak and fire in a process plant.
  2. Flanged pipe systems need much more space (just think of a pipe rack).
  3. Insulation of flanged pipe systems is more expensive (special flange caps).