Pipe flanges

Pipe flanges are basically plates or rings used to connect pipes, valves and other piping equipment to form a piping system.

Pipe flanges are the second most used joining method after welding. They are used when joints need dismantling. It provides flexibility for maintenance. Flange Connects the pipe with various equipment and valves. Breakup flanges are added to the pipeline system if regular maintenance is required during plant operation.

Manufacturing Standards of Welded Fittings

A flange standard lays down the dimensions, surface finish, facing type, marking, material and technical specifications for flanges.
ASMEANSI B16.9, ANSI B16.28, MSS-SP-43
DINDIN2605, DIN2615, DIN2616, DIN2617, DIN28011
ENEN10253-1, EN10253-2
ASTM A403 – ASME SA403Standard Specification for Wrought Austenitic Stainless Steel Piping Fittings
ASME B16.9Factory-Made Wrought Fittings Buttwelding
ASME B16.25Buttwelding Ends
ASME B16.28Wrought Steel Short Radius Elbows and Buttwelding Returns
MSS SP-43Wrought and Fabricated Butt-Welding Fittings for Low Pressure, Corrosion Resistant Applications

Stainless steel flange

Carbon steel flange

Speciality Flange

Applications Of Flanges

A flange is a method of connecting pipes, valves, pumps, and other equipment to form a piping system.

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Flange size & tolerance

Our company offers a wide range of flanges like PL, SW, BL, WN,SO,LJ, ASME/ANSI B16.5 etc., which is precisely engineered in

flange dimensions

Chemical Analysis(%) For Part Standard

The usual materials of flanges include stainless steel, carbon steel, aluminum and plastic.

Tensile Property For Part Standard of flange

StandardGradeYield Strengh(Mpa)Tensile Strengh(Mpa)HardnessElongation(%)

Flange Types in three groups

Remember the types of flanges described in the beginning of this article? (Welding Neck, Slip-On, Threaded, Socket Weld, Lap-Joint and Blind), well those were the standard types, now you’ll see that the types of flanges available in the type of the flange is very similar to them, so all the “pros” and “cons” described there can be applied here.

The types divided the flanges in three groups: loose, integral and optional. Below I’ll describe these types according to the Code.

Loose Type Flanges

This type covers those designs in which the flange has no direct connection to the nozzle neck, vessel, or pipe wall, and designs where the method of attachment is not considered to give the mechanical strength equivalent of integral attachment.

Integral Type Flanges

This type covers designs where the flange is cast or forged integrally with the nozzle neck, vessel or pipe wall, butt welded thereto, or attached by other forms of arc or gas welding of such a nature that the flange and nozzle neck, vessel or pipe wall is considered to be the equivalent of an integral structure. In welded construction, the nozzle neck, vessel, or pipe wall is considered to act as a hub.

Optional Type Flanges

This type covers designs where the attachment of the flange to the nozzle neck, vessel or pipe wall is such that the assembly is considered to act as a unit, which shall be calculated as an integral flange, except that for simplicity the designer may calculate the construction as a loose type flange provided none of the following values is exceeded: g0 = 5/8″ (16 mm), B/g0 = 300, P = 300 psi (2 MPa) and operating temperature = 700°F (370°C).


Pipe Flange Standards mainly include three systems in the world, ANSI/ASME flange system(American), DIN flange system(European system), JIS flange system, other system made according to this three systems, like GB flange standard, which mainly made according to ANSI/ASME and DIN flange standard, Duwa Piping supplies those flanges with top quality and soonest delivery time.

ASME standards

ASME B16.1 – Gray Iron Pipe Flanges and Flanged Fittings: Classes 25, 125, and 250
ASME B16.5 – Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard
ASME B16.20 – Ring Joint Gaskets and Grooves for Steel Pipe Flanges
ASME B16.21 – Nonmetallic Flat Gaskets for Pipe Flanges
ASME B16.24 – Cast Copper Alloy Pipe Flanges and Flanged Fittings: Classes 150, 300, 600, 900, 1500, and 2500
ASME B16.34 – Large Diameter Steel Flanges (NPS 26 through NPS 60)
ASME B16.36 – Orifice Flanges
ASME B16.42 – Ductile Iron Pipe Flanges and Flanged Fittings: Classes 150 and 300
ASME B16.47 – Large Diameter Steel Flanges (NPS 26 Through NPS 60)

ASTM standards

ASTM A105 – Specification for Carbon Steel Forgings for Piping Applications
ASTM A182 – Specification for Forged or Rolled Alloy Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High Temperature Service
ASTM A193 – Specification for Alloy Steel and Stainless Steel Bolting Materials for High Temperature Service
ASTM A194 – Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure and High Temperature Service
ASTM A694 – Specification for Carbon and Alloy Steel Forgings for Pipe Flanges, Fittings, Valves, and Parts for High-Pressure Transmission Service
ASTM A707 – Specification for Flanges, Forged, Carbon and Allow Steel for Low Temperature Service

AWWA standards

AWWA C115 – Standard for Flanged Ductile Iron Pipe with Ductile-Iron or Gray-Iron Threaded Flanges

ISO standards

ISO 5251 – Stainless steel butt-welding fittings

MSS standards

MSS SP-6 – Standard Finishes for Contact Faces Pipe Flanges and Connecting End Flanges of Valves and Fittings
MSS SP-9 – Spot Facing for Bronze, Iron and Steel Flanges
MSS SP-25 – Standard Marking Systems for Valves, Fittings, Flanges, and Unions
MSS SP-44 – Steel Pipeline Flanges
MSS SP-53 – Quality Standards for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Components – Magnetic Particle
MSS SP-54 – Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components – Radiographic
MSS SP-55 – Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components – Visual
MSS SP-75 – High Test Wrought Butt Welding Fittings
MSS SP-106 – Cast Copper Alloy Flanges and Flanged Fittings Class 125,150, and 300
ASME B16.5 and ASME B16.47 cover pipe flanges up to NPS 60 (B16.5 from 1/2″ to 24″ and B16.47 from 26″ to 60″). ANSI B16.47 covers two series of flanges, Series A is equal to MSS SP-44-44, and Series B is equal to API 605 (API 605 has been canclled).


Only the most used flange classes are listed on this page. For more information on flanges and their respective standards, please follow the link below.

150 300 400 600 900 1500 2500

The concept of flange ratings likes clearly. A Class 300 flange can handle more pressure than a Class 150 flange, because a Class 300 flange are constructed with more metal and can withstand more pressure. However, there are a number of factors that can impact the pressure capability of a flange.

The Pressure Class or Rating for flanges will be given in pounds. Different names are used to indicate a Pressure Class.
For example: 150 Lb or 150 Lbs or 150# or Class 150, all are means the same.

The concept of flange ratings likes clearly. A Class 300 flange can handle more pressure than a Class 150 flange, because a Class 300 flange are constructed with more metal and can withstand more pressure. However, there are a number of factors that can impact the pressure capability of a flange.
The Pressure Class or Rating for flanges will be given in pounds. Different names are used to indicate a Pressure Class.
For example: 150 Lb or 150 Lbs or 150# or Class 150, all are means the same.

ASME B16.5 covers flanges with a nominal size from 1/2″ through 24″. It also includes classes from ANSI 150 through ANSI 2500. The flanges included in B16.5 are blind, lap joint, socket, slip-on, threaded and weld neck flanges.

ASME B16.47 covers flange with a nominal size of 24″ and larger. The flange classes it covers are from ANSI 75 through ANSI 900. The flanges included are blind and weld neck flanges. Additionally, B16.47 has two series of flanges, Series A (similar to ASME MSS SP44) & Series B (similar to API 605). Series A flanges are larger, heavier and have fewer bolt holes. The reason for series A and series B is that both specifications mentioned before were brought together to be covered under ASME B16.47.


There are three primary types of flange facings. Not all facings are available with each end connection. This is based on the design of the flange and design of the piping system.

The typical flange facings are:

Flange facing types

Raised Face Flanges (RF)

Raised face flange has a small portion around the bore is raised from the face. The gasket seat on this raised face. The height of the raised face depends on the flange pressure-temperature rating that is known as a class of the flange. For 150# & 300# height of the raised face is 1/6” and above 300# it is 1/4”. The inside bore circle type of gasket is used with a raised face flange.

Flat Face Flanges (FF)

As the name suggests, the flat face flange has a flat face. Flat face flanges are used when the counter-flanges are flat faces. This condition occurs mainly in connection to Cast Iron equipment, valves, and specialties. A full-face gasket is used when a flat face flange is used.

Ring Type Joint Flanges (RTJ)

Ring joint type face flange has a specially designed grove in which metal gasket seat. This type of flange is used in high pressure and temperature services.

Frequently used astm grades

MaterialFittingsFlangesValvesBolts & Nuts
Carbon SteelA234 Gr WPAA105A216 Gr WCBA193 Gr B7
A194 Gr 2H
A234 Gr WPBA105A216 Gr WCB
A234 Gr WPCA105A216 Gr WCB
Carbon Steel
A234 Gr WP1A182 Gr F1A217 Gr WC1A193 Gr B7
A194 Gr 2H
A234 Gr WP11A182 Gr F11A217 Gr WC6
A234 Gr WP12A182 Gr F12A217 Gr WC6
A234 Gr WP22A182 Gr F22A217 Gr WC9
A234 Gr WP5A182 Gr F5A217 Gr C5
A234 Gr WP9A182 Gr F9A217 Gr C12
Carbon Steel
Alloy Low-Temp
A420 Gr WPL6A350 Gr LF2A352 Gr LCBA320 Gr L7
A194 Gr 7
A420 Gr WPL3A350 Gr LF3A352 Gr LC3
Austenitic Stainless SteelA403 Gr WP304A182 Gr F304A182 Gr F304A193 Gr B8
A194 Gr 8
A403 Gr WP316A182 Gr F316A182 Gr F316
A403 Gr WP321A182 Gr F321A182 Gr F321
A403 Gr WP347A182 Gr F347A182 Gr F347
ASTM standards define the specific manufacturing process of the material and determine the exact chemical composition of pipes, fittings and flanges, through percentages of the permitted quantities of carbon, magnesium, nickel, etc., and are indicated by "Grade".

Flange materials acc. to ASTM

The most common materials for pipe flanges (forged grades) are: ASTM A105 (carbon steel high temperature to match A53/A106/API 5L pipes), A350 Grades LF1/2/3 (carbon steel low temperature to match A333 pipes), A694 Grades F42 to F80 (high yield carbon steel to match API 5L pipe grades), ASTM A182 Grades F5 to F91 (alloy steel flanges to match A335 pipes), A182 Grade F304/316 (stainless steel flanges to match A312 SS pipes), A182 Gr. F44/F51/F53/F55 (duplex and super duplex to match A790/A928 pipes) and various nickel alloy grades (Inconel, Incoloy, Hastelloy, Monel).

The material qualities for these flanges are defined in the ASTM standards.

What are ASTM Grades?
For example, a carbon steel pipe can be identified with Grade A or B, a stainless-steel pipe with Grade TP304 or Grade TP321, a carbon steel fitting with Grade WPB etc.

Chemical Composition (%) of ASTM A403

Steel No.TypeCSiSPMnCrNiMoOtheróbósδ5

For each reduction of 0.01% below the specified C maximum, an increase of 0.06% Mn above the specified maximum will be permitted, up to a maximum of 1.35%.
The sum of Cu, Ni, Cr, and Mo shall not exceed 1.00%.
The sum of Cr and Mo shall not exceed 0.32%.
The maximum carbon equivalent (C.E.) shall be 0.50, based on heat analysis and the formula C.E.=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

Flanged connection

There are many ways to connect flanges, including threading, welding or bolting. The threaded flange is best for low pressure or smaller pipelines because it can maintain its seal. When your pipeline is larger or high pressure, then the welded flange is preferable. A boiler room is one place where welded blind flanges might be used, due to the high pressure involved.

flanged connection

Flanged joints: flanges, bolts and nuts and gaskets

A flange is a external rib at the end of pipes, valves and other flow devices to assemble them.

Dimensions of the flanges are up to specific Standards : DIN, ANSI, AS, BS, JIS

A flanged connection requires two flanges (the “main” and the “companion”), a set of bolts and nuts (whose number depends on the flange diameter and class) and two sealing gaskets. Flanged connections have to be executed and supervised by trained personnel, as the quality of the joint has a critical impact on the performance of the piping system / pipeline (the standard TSE – TS EN 1591 Part 1-4, “Flanges and their joints”, defines a number of requirements for the execution of proper flanged connections). Whereas all elements of the joint are critical, experience shows most leaks are originated by the improper installation of the sealing elements, i.e. the gaskets.

The typical pipe to flange connections are welded or threaded. Welded flanges are used for pipelines and piping systems with high pressures and temperatures, and with diameters above 2 inches.

Threaded connections are instead used for installations of smaller diameter and not subject to severe mechanical forces such as expansion, vibration, contraction, oscillation (forces that would crack the threaded joint). In all these critical cases, butt weld connections are recommended.


Steel flanges must be packed with seaworthy packing method then delivery to customers, usually the packing way include wooden box, wooden pallet, iron & steel cage, iron & steel pallet etc.

Flange Inspection

Before dispatching from manufacture each flange is inspected to ensure quality. During an inspection you have to check the following;

  • 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

ASME B16.5 and B16.47 standards cover permissible tolerances for inspection.

Marking on the flange

Shipping mark stick to outside of package. Following shall be marked on flange body

marking of steel flanges
  • 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)

Packing Because of the normal wooden boxes or wooden pallets have to do fumigation treatment, we usually use plywood pallet or plywood case or box to pack steel flanges without fumigation treatment.