What are Steel Flanges?

What are Steel Flanges?

Generally speaking, the steel flanges refer to the joints specially used for connecting pipes. For example, two steel pipes with a diameter of 100 can be connected by welding or electric welding. Once welded, it is not easy to disassemble unless it is cut by a cutter or electric welding to cut open. However, if a flange (usually a round flange) is used, a gasket seal can be added and then fixed with a screw cap. It can also be easily disassembled when the pipeline fails or is overhauled. In addition, if there are flanges on both sides of the large gate valve switch, it is convenient to remove the switch.

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Types of flanges

Common flange types

Welding Neck Flanges

stainless steel raised face weld neck flanges - What are Steel Flanges?

The welding neck flanges is normally referred to as the high hub flange. It is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the flange.

A weld neck flange (also known as a high-hub flange and tapered hub flange) is a type of flange. There are two designs. The regular type is used with pipes. The long type is unsuitable for pipes and is used in process plant. A weld neck flange consists of a circular fitting with a protruding rim around the circumference. 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.

WELDING NECK FLANGE NPS 6, CLASS 150, SCHEDULE 40, ASME B16.5 / ASTM A105

WELDING NECK FLANGE NPS 6 - What are Steel Flanges?

The flange above has 8 bolt holes, and a welding bevel of 37.5 degrees (red circle). All given dimensions are in millimeters. The raised face (RF) does not need to be specified, because according to ASME B16.5, each flange is standard delivered with a raised face. Only a different design (Ring Type Joint (RTJ), Flat Face (FF) etc.), should be specified.

The welding neck flange is the best designed butt-welded flange of those currently available becuase of its inherent structural value.

Butt weld flanges are mainly used in applications where the working conditions are more demanding, such as the thermal expansion or other load of the pipeline, the stress on the flange is large or the stress changes are repeated, the pipeline with high pressure and temperature fluctuations or high temperature and high pressure Zero-low temperature pipeline. The welding flange is not easy to be deformed, sealed, and widely used. The nominal pressure is about PN1.0MPa~PN25.0MPa.
According to the type of sealing surface, the welding flange can be divided into: flat butt welding flange, protruding facing welding flange, concave and convex facing welding flange, groove facing welding flange, ring connection facing welding flange.

Slip-On Flanges

slip on flanges banner - What are Steel Flanges?

Slip-On flanges or SO flanges are commonly lower in price than weld-neck flanges, and to this effect are a popular choice for our customers.

Slip-On Pipe Flanges. As made obvious by their name, these pipe flanges slip over the pipe. They’re manufactured with an inside diameter that is slightly bigger than the pipe’s outside diameter. These attachments are connected to the pipe via fillet weld at the top and bottom of the flange.

However, customers should bear in mind that this initial cost saving may be diminished by the additional cost of the two fillet welds required for proper installation. Moreover, weld-neck flanges have a higher life expentancy than slip-on flanges under duress.

Slip-on flanges are all bored slightly larger than the O.D. of the pipe. They are preferred over welding neck flanges bu many users due to their lower intial cost, but final intallation cost is probably not much less than that of the welding neck flange because of the additional welding involved.

Weldneck and Slip-On Orifice Runs

Weldneck and Slip On Orifice Runs - What are Steel Flanges?

In general, SO flanges are used with flat weld rings in one of three situations:

  1. Save costs. When the material of the pipe is special and expensive, the flange of the same material is costly.
  2. It is inconvenient to weld or inconvenient to process or requires high strength. Such as plastic pipes, glass steel pipes and the like.
  3. Easy to construct. If the flange bolt hole is connected when connecting, it is not easy to find or prevent the flange bolt hole of the equipment to be changed in the future.

Disadvantages of using a SO flange:

  1. Understand low pressure.
  2. Low strength at the weld ring (especially when the thickness is less than 3mm)

Socket Welding Flanges

stainless steel raised face socket weld flanges - What are Steel Flanges?

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 counterbore is slightly larger than the O.D. of the matching pipe, allowing the pipe to be inserted into the flange similar to a slip-on flange.
The diamter of the smaller bore is the same as the I.D. of the matchine pipe A restriction is built into the bottom of the bore which sets as a shoulder for the pipe to rest on.
When using a socket weld flange, the inner diameter needs to be the same as the inner diameter of the pipe. The socket flange is only suitable for pipes with a nominal diameter of 150 or less.

Lap Joint Flanges

stainless steel lap joint flanges - What are Steel Flanges?

Lap Joint Flanges (LJ Flanges) are used on piping fitted with lapped pipe or with lap joint stub ends the combined initial cost of the two items being approximately one-third higher than that of comparable welding neck flanges.
Lap joint flange is having two components, a stub end, and a loose backing flange. Stub end is butt welded to the pipe and Backing flange freely move over the pipe. The backing flange can be of different material than stub material and normally of the carbon steel to save the cost. Lap flange is used where frequent dismantling is required, and space is constrained.
The lap joint flange is practically identical to a slip-on flange except it has a radius at the intersection of the bore and flange face.
The lap joint flange is practically identical to a slip-on flange except it has a radius at the intersection of the bore and flange face. This radius is necessary to have the flange accommodate a lap joint stub end. Normally, a lap joint flange and a lap joint stub end are mated together is an assembly system.

Threaded Flanges

stainless steel raised face threaded flanges - What are Steel Flanges?

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 flanges are widely demanded as pipe flanges i.e called as threaded pipe flanges used in different industrial applications.
This type of joint connection is Speedy and simple but not suitable for high presser and temperature applications. Threaded Flanges are mostly used in utility services such as air and water.
Threaded (Screwed) flange is similar to the Slip-On flange, but the bore is threaded. Its chief merit is that it can be assembled withour welding, explaining its use in low pressure services at ordinary atmospheric temperatures, and in highly explosive areas where welding create a hazard.
Under conditions where the temperature of the pipe changes sharply or the temperature is higher than 20 ° C and lower than -45 ° C. We recommend not using threaded flanges to avoid leakage.
The sealing surface type of the threaded flange has two types: full plane and protruding surface. Consider the structural characteristics of the threaded flange. Therefore, it is not suitable for use in flammable/explosive and high and extreme hazard situations. Small nuclear pressure, such as air conditioning water system, can be used safely.

Thread of threaded flanges

Threaded flanges of pn0.6, PN/1.0, PN1.6, PN2.5 and PN4.0 shall adopt 55 cylindrical pipe thread conforming to GB / T 7306.1 or 55 conical pipe thread conforming to GB / T 7306.2; Threaded flanges of PN2.0, PN5.0, PN11.0 and PN15.0mpa shall adopt 60 conical pipe threads in accordance with GB / T 12716; Unless otherwise specified.
The thread axis shall be concentric with the flange axis, and the deviation shall not exceed 5 mm / m. Flanges of PN0.6 ~ PN4.0 do not have countersunk holes. The threads shall be chamfered to the large diameter of the threads on the back of the flange, and the angle shall be approximately 45% with the thread axis. Countersunk holes shall be machined on the back of flanges of PN5.0 ~ PN15.0, and the threads shall be chamfered to the inner diameter of the countersunk holes, and the angle shall be approximately 45% with the thread axis. The thread chamfering and countersunk hole chamfering shall be concentric with the threads.
The detection of threads shall comply with the provisions of relevant standards.

Standard      

The screw thread(M)/Screw hole(φ)size

JB series 2             

M22/φ25

(all)

M30/φ34

(Part of the)

M36/φ41

(Part of the)

M42/φ48

(all)

M48/φ54

(all)

new HG,ISO,JBA series of1,BS, Γ ΟCT,DIN

M2-M24 / φ 26

M33 / φ 36

M33 / φ 36

M39 / φ 42

M45 / φ 48

M45 / φ 48

When two part flange is used

Measures taken

The first row is flanged

Screw hole reaming1mm

The first row is flanged

Screw hole reaming2mm

Add the gasket

Add the gasket

consistent

Add the gasket

Blind Flanges

stainless steel raised face blind flanges - What are Steel Flanges?

A Blind flange is round plate which has all of the relevant boltholes but no center hole, and because of this feature this flange is used to close off the ends of a piping systems and pressure vessel openings. It also permits easy access to the interior of a line or vessel once it has been sealed and must be reopened.

The blind flange is used to close ends of piping systems. It is a kind of round plate with no center hold but with all the proper bolt holes. This blind flange is available in various sizes and materials and is used to provide positive closer on the ends of pipes, valves or equipment nozzles. This flange helps in easy access to a line once it has been sealed. The blind flange is sometimes custom made or machined to accept a nominal sized pipe to which reduction is being made.

We are manufacturer of Blind Flanges and supply high quality Blind Flanges in both large and small quantities worldwide and offer you the best prices in the market.

Blind Flanges are commonly used in petrochemical, pipe engineering, public services & water works.
Blind pipe flanges are often used for high pressure applications.

This reduction can be a threaded reduction or welded reduction.

Details of Blind flanges

flg bl det - What are Steel Flanges?

  1. Blind flange
  2. Stud Bolt
  3. Gasket
  4. Other flange

Specialty flange

Orifice Flanges

orifice flanges banner - What are Steel Flanges?

An Orifice Flange is intended for use instead of standard pipe flanges when an orifice plate or flow nozzle must be installed. Pairs of pressure tapings are machined into the Orifice Flange, making separate orifice carriers or tapings in the pipe wall unnecessary. This type of flange includes the orifice plate with data tap, a pair of flanges with integrated taps, a set of gaskets, bolts and nuts and a jackscrew to assist separating the flanges for orifice inspection.
Design can be with RF or RTJ weld neck flanges or RF slip-on flanges. The orifice plates are centered within very close tolerances of the standards.
An Orifice plate is a device used for measuring flow rate. Either a volumetric or mass flow rate may be determined, depending on the calculation associated with the orifice plate. It uses the Bernoulli’s principle which states that there is a relationship between the pressure of the fluid and the velocity of the fluid. When the velocity increases, the pressure decreases and vice versa.
An Orifice plate is a thin plate with a hole in the middle. It is usually placed in a pipe in which fluid flows. When the fluid reaches the orifice plate, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracta point As it does so, the velocity and the pressure changes. Beyond the vena contracta, the fluid expands and the velocity and pressure change once again. By measuring the difference in fluid pressure between the normal pipe section and at the vena contracta, the volumetric and mass flow rates can be obtained from Bernoulli’s equation.
When installing the orifice plate flange the pressure taps need to be at the same elevation to each other. The assumption when making the calculation for the orifice plate is that static head of the tubes is the same on both sides of the orifice plate. Pressure taps should not be installed facing down as the taps could become plugged with debris in the line.
Weld Neck Orifice Flanges are butt-welded into the pipeline. The inside diameter (bore diameter) of the pipe should be specified when ordering. Weldneck orifice flanges are available in ANSI classes 300, 600, 900, 1500 and 2500. They are not available in ANSI 150 sizes because the thickness of ANSI 150 flanges are not enough to allow for drilling pressure taps.

Installing the orifice plate flange

Orifice flanges are installed in a straight run of pipe in order to avoid turbulence at the plate. As a rule of thumb, an orifice flange has ten diameters of straight pipe upstream and five diameters of pipe downstream.

Orifice Flange Union - What are Steel Flanges?

Orifice Flange Union

Pipe Tap - What are Steel Flanges?

Pipe Tap

Jack Screw - What are Steel Flanges?

Jack Screw

Pipe Taps - What are Steel Flanges?

Pipe Taps

When installing the orifice plate flange the pressure taps need to be at the same elevation to each other. The assumption when making the calculation for the orifice plate is that static head of the tubes is the same on both sides of the orifice plate. Pressure taps should not be installed facing down as the taps could become plugged with debris in the line.

Weldneck orifice flanges are butt-welded into the pipeline. The inside diameter (bore diameter) of the pipe should be specified when ordering. Weldneck orifice flanges are available in ANSI classes 300, 600, 900, 1500 and 2500. They are not available in ANSI 150 sizes because the thickness of ANSI 150 flanges are not enough to allow for drilling pressure taps.

Expander Flange

Expander Flange - What are Steel Flanges?

An Expander Flange is a type of welding neck pipe flange used to increase pipe size at the flange connection (see sketch).

The Expander Flange is normally referred to as the high hub flange. It is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the flange.

An Expander Flange is a type of welding neck pipe flange used to increase pipe size at the flange connection (see sketch). Expander flanges are also known as a cost effective alternative to using a separate reducer-welding neck flange combination.

Expander flanges are also known as a cost effective alternative to using a separate reducer-welding neck flange combination. The expander flange is available in a range of sizes and materials.

An expander flange is similar to a weld neck flange but with the hub expanding to a larger size (one or two sizes). If you have limited space or just need to connect to a larger pipe size, it provides a convenient way for equipment, pumps and valves. It can replace the use of a flange and reducer. Pressure ratings and dimensions are in accordance with ANSI/ASME B16.5.

Dimensions of Expander Flanges

Dimensions of Expander Flanges - What are Steel Flanges?

It’s compact size saves space when compared to a reducer-welding neck flange. This flange has a raised face.

Only one butt-weld is needed to install the Expander Flange Very cost effective and competitively priced.

Spectacle flange (Figure-8 Blanks)

spectacle blindflange draws - What are Steel Flanges?

The spectacle flange is also called the figure-8 blanks. As the name implies, it is shaped like a 8 word. It has a blind plate at one end and a throttle ring at the other end. When the fluid is transported, the throttle ring is used. The use of a blind plate is somewhat like the function of a shut-off valve, which can be used to cut off when the valve leaks, and its sealing performance is better. For systems that require complete isolation, they are generally chosen as a reliable means of isolation. There should be 2 stop valves before and after the spectacle blind flange. When all are in the closed state, the spectacle flange’s state is changed. Common heat exchangers are used and standby, reactors are used and standby, nitrogen lines and process line connections are available, and the like. Another feature is that the logo is obvious and easy to identify its installation status.
The main function of the eight-character blind plate is to completely block, just like a gate valve with 100% performance and no misoperation.

General purpose:

  1. System type media pipelines, such as steam purge pipelines and oil-based process media pipelines, provide a safe isolation. At this time, the spectacle flange should be installed on the side close to the system media pipeline. Of course, in order to remove the 8-word blind plate online, there should be a gate valve on the side close to the process medium pipeline. Such a spectacle flange is generally marked as normally closed.
  2. The double-gate valve should be installed in the flammable or toxic medium pipeline of the inlet and outlet device. The spectacle flange is installed in the double-gate valve. Such spectacle flange is generally marked as normally open.
  3. The device will be used when driving, and the gate valve should be installed in the pipeline that no longer passes through the medium after driving normally. The spectacle flange is installed on the side of the pipeline with normal five medium circulation, and the spectacle flange is generally marked as normally closed.

The spectacle flange should be selected to match the flange that holds it. The length of the bolt used for clamping should be appropriately lengthened according to the thickness of the blind plate.

Long Weld Neck Flanges

The Long Weld Neck Flange is normally referred to as the high hub flange. It is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the flange.

NW Long Weld Neck Flanges - What are Steel Flanges?

The Long Weld Neck Flanges are the best designed butt-welded flange of those currently available becuase of its inherent structural value. It is expensive because of the design.

Long welding neck flange, lwn flanges are similar to a standard Welding Neck flanges, but the “Neck” is considerably longer than other flanges. LWN flange is often used as a nozzle for a barrel or column. In addition, there are the type LWN Heavy Barrel (HB) and the Equal LWN Barrel (E); they have a different shape and a thicker “Wall”.

Reducing Flange

Reducing flanges are a specialty flange that are most often used on projects that require the fitting together of different sized pipes.
reducing flange banner - What are Steel Flanges?

A reducing flange consists of a flange with one specified diameter having a bore of a different and smaller, diameter. Except for the bore and hub dimensions, the flange will have dimensions of the larger pipe size.

Reducer flange draws:

There are several types of reducing flanges including weld-neck reducing flanges, slip-on reducing flanges and threaded reducing flanges.

Reducing Flange can be fabricated using a reducing spool with concentric or eccentric reducer & desired flange at each end OR it could be a single flange with internal reduced bore to connect different sized fittings on either sides.

How to connect reducing flange?

reducing slip on flange - What are Steel Flanges?
reducing slip-on flange
reducing weld neck flange - What are Steel Flanges?
reducing weld neck flange
weld neck flange and reducing slip on flange - What are Steel Flanges?
Weld neck flange and 
reducing slip-on flange
  • Weld Neck and Slip-On: Connect the flange sides that match the higher diameter of pipe and complete welding process. Repeat the welding process for the smaller size of pipe on the other side of the reducing flange. Now both sizes of pipes are connected through the reducing process. Take enough care to ensure that the inside diameters of the pipes are properly aligned with the ID of the Flange on both sides.
  • Threaded Flange: First connect any one size of pipe by threading to one side of the flange. Make sure that the pipe is inserted to reach the required depth inside the flange. Repeat the same process for the other size of the pipe.
  • In high pressure and temperature applications, welding is done on the outside of the pipe after threading to increase the strength of the joint.

Designed for use in changing diameters in a piping system. A reducing flange consists of a flange with one specified diameter having a bore of a different and smaller, diameter

Except for the bore and hub dimensions, the flange will have dimensions of the larger pipe size.

Weldoflange/Nipoflange

The Weldoflange and Nipoflange is a combination of a Welding Neck flange and a supposedly Weldolet or Nipolet.

Two different pipe branch connections

On the run pipe side a nipoflange is designed like a weldolet. That means the branch connection on the run pipe side is a welding connection. On the other side there it has a flange connection. The flange connection can be designed according to customers requirements (acc. To DIN or ANSI).

Forged material
A nipoflange similar to ANSI B 16.9 or MSS-SP 97 is manufactured from forged material. That means a nipoflange is a forged fitting without welding seam.
WAZ (acceptance test certificate)
Of course, you may obtain a standard cert. 3.1 with each delivery. Upon request, we are able to deliver a cert 3.2 (normally TüV or other inspection institutions). In the cert. 3.1, the chemical consistenc and the physical characteristics of the material are listed.

Standard and special materials
Anthermo is able to deliver nipoflanges in standard materials. Upon request special materials are also deliverable.

The Weldoflange and Nipoflange is a combination of a Welding Neck flange and a supposedly Weldolet or Nipolet. The 2 components are manufactured in one piece, and not welded. These flanges are primarily in Branch connections. Furthermore, they have an expanded range of special flanges, fittings and branch connections.

nipo flanges draw - What are Steel Flanges?

Flanges Materials

Carbon Steel Flanges Materials

  • Astm A105 (high-temperature Carbon Steel Flange: General Service Such As Oil, Oil Vapor, Gas, Steam And Water At Temperatures -20°f To 1000°f (-28°c To 537°c))
  • Astm A350 Lf1 (low-temperature Carbon Steel Flange: Low-temperature Service Down To -50°f And Not Above 650°f (-46°c And Not Above 343°c))
  • Astm A694 F42/f46/f48/f50/f52/f56/f60/f65/f70(high Yield Carbon Steel Flange)

Stainless Steel Flanges Materials

  • Astm A182 F304/f304h/f304l/f304n/f304ln/f309h/f310/f310h/f310moln/f316/f316h/f316l/f316n/f316ln/f316ti/f317/f317l/f321/f321h/f347/f347h/f348/f348h/904/904l

Alloy Steel Flanges Materials

  • Astm A182 Gr. F1/f2/f5/f5a/f9/f11 Cl.2/f12 Cl.2/f22 Cl.3/f91 (alloy Steel Flanges)

Duplex And Super duplex Flanges Materials

  • Astm A182 F51 (uns S31803/uns S31803)/f53 (uns S32750)/f55 (uns S32760)

Super Alloy Steel Flanges Materials

  • 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)
  • Hastelloy X
  • Monel R-405
  • Monel K-500
  • Hastelloy C-22
  • Hastelloy B-2
  • Inconel 718
  • Inconel Alloy 601
  • Alloy 20
  • Nickel 201
  • Monel R-405
  • Monel K-500
  • Inconel 718
  • Hastelloy C-22
  • Hastelloy B-2
  • Hastelloy B-3

Titanium Flanges Materials

  • Astm B381 Gr.2 (titanium)

Flange Inspection

Following to be confirmed during inspection of flange

  • 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

Permissible tolerances are given in B16.5 and B16.47 standard.

Flange Inspection - What are Steel Flanges?

Place one end of a tape measure on the inside of the flange. The diameter is used to determine what size pipe a flange can be used with, so you must find this information by using the inside of the flange as opposed to the outside.

Stretch your tape measure across the center of the circular shape of the flange until it touches the other side of the unit. Keep this end of the tape measure on the inside of the flange as well. Because the flange is circular in shape, the tape measure must stretch across the exact center of the flange to provide an accurate measurement.

How to Measure a Flange?

A flange is a circular piece of equipment used to connect two pipes together. Flanges can be made out of stainless steel, copper or any other type of metal. They typically match the metal of the pipes they connect. Flanges help seal the pipes together, preventing water from leaking when it passes from one pipe to another along the way from its origin to its destination.

Flange Dimensions - What are Steel Flanges?

Place one end of a tape measure on the inside of the flange. The diameter is used to determine what size pipe a flange can be used with, so you must find this information by using the inside of the flange as opposed to the outside.

Stretch your tape measure across the center of the circular shape of the flange until it touches the other side of the unit. Keep this end of the tape measure on the inside of the flange as well. Because the flange is circular in shape, the tape measure must stretch across the exact center of the flange to provide an accurate measurement.

Although the dimension of the flange diameter is just one measurement used when identifying your flange, it is an incredibly crucial one when lining this piece up to your system.

Getting started with measurement — the devil is in the details

There are three separate steps when discussing the measurement of the flange diameter. First, measuring the flange’s inside diameter, then across center of the flange and finally, the outside diameter.

Step 1 – Start by measuring inside the flange by simply measuring the center hole. This diameter lets you know what size pipe should be paired with the flange. If you have documentation that tells you the inside measurement of the flange and pipe, make sure you have the right documentation for the part. Papers can get mixed up easily, so it never hurts to take a quick measurement to verify independently.

Step 2 – Measure across the center of the flange. Make sure you find the exact center of the flange to get an accurate dimension. You’ll notice that the bolt holes around the flanges are distributed evenly. This will help guide you to the center.

Step 3 – Finally, measure around the outside diameter of the flange. If your system is squeezed into a tight space, a flange that is too thick may cause problems and some other pipes may need to be moved. Knowing the outside diameter will help you plan for this.

That’s really about all that needs to be done when measuring the diameter of a flange. However, it’s easy to acquire some false confidence and skip one or more of these steps. Be sure to watch the details, which will ensure a much better installation.

If you’re building a new system, this is an opportunity to buy the pipes and flanges specifically manufactured to fit together according to widely accepted standards. Obviously, this will eliminate chances for error. Beyond the measurement, keep in mind what type of fluid will be passing through the system, the temperature of both the fluid inside, the working conditions outside, and of course, the material used to create the flange.

Some pipe/flange materials will not play nice with the chemicals passing through. Make sure you understand the demands the system will create.

Flange Tolerance

Tolerance of Welding Neck Flanges

Outside Diameter When O.D. is 24″ or less  ±1.6mm﹡
Inside Diameter 10″ and smaller  ±0.8mm
12″ thru 18″  ±1.6mm
20″ and larger  +3.2mm, -1.6mm
Outside Diameter of hub 5″ and smaller  +2.4mm, -0.8mm﹡
6″ and larger  +4.0mm, -0.8mm
Diameter of contact face 1/16″ rasied face tongue and groove male, female  ±0.8mm
1/4″ rasied face tongue and groove male, female  ±0.4mm
Diameter of hub at base when hub base is 24″ or smaller  ±1.6mm﹡
Diameter of hub at point of welding 5″ and smaller  +2.4mm, -0.8mm
6″ and larger  +4.0mm, -0.8mm
Drilling Bolt circle  ±1.6mm
Bolt hole spacing  ±0.8mm
Eccentricity of bolt circle with respect to facing 2 1/2″ and smaller: 0.8mm, max﹡
Eccentricity of bolt circle with respect to bore 3″ and larger: 1.6mm, max﹡
Thickness 18″ and smaller  +3.2mm, -0mm
20″ and larger  +4.8mm, -0mm
Length of thru hub 10″ and smaller  ±1.6mm
12″ and larger  ±3.2mm

Tolerance of Threaded Flanges, Socket Welding Flanges, Slip-On Flanges

Lap Joint Flanges and Blind Flanges

Outside Diameter When O.D. is 24″ or less  ±1.6mm﹡
Inside Diameter Threaded Within limits on boring gauge
Socket welding, Slip-on and Lap joint, 10″ and smaller  +0.8mm, -0mm
Socket welding, Slip-on and Lap joint, 12″ and larger  +1.6mm, -0mm
Outside Diameter of hub 5″ and smaller  +2.4mm, -0.8mm﹡
6″ and larger  +4.0mm, -0.8mm
Diameter of contact face 1/16″ rasied face tongue and groove male, female  ±0.8mm
1/4″ rasied face tongue and groove male, female  ±0.4mm
Diameter of counterbore same as for inside diameter
Drilling Bolt circle ±1.6mm
Bolt hole spacing ±0.8mm
Eccentricity of bolt circle with respect to facing 2 1/2″ and smaller: 0.8mm, max﹡
Eccentricity of bolt circle with respect to bore 3″ and larger: 1.6mm, max﹡
Thickness 18″ and smaller  +3.2mm, -0mm
20″ and larger  +4.8mm, -0mm
Length of thru hub 10″ and smaller  ±1.6mm
12″ and larger  ±3.2mm

Dimensional tolerances for AWWA pipe flanges

Listed below are the Dimensional Tolerances to which flanges are manufactured. 

Ring type Slip-on and Blind flanges HUB type slip-on
O.D. <=24″ +/- 0.6″(1.6mm) O.D. <=24″ +/- 0.6″(1.6mm)
>24″ +/- .12″(3.2mm) >24″ +/- .12″(3.2mm)
I.D. Socket-Welding 10″ and Samller
+.03″(0.8mm),-0″
I.D. 10″ and Samller +.03″(0.8mm)
Slip-on and 
Lap Joint
12″ and Larger
+.06″(1.6mm),-0″
12″-18″ +/-.06″(1.6mm)
20″-42″ +.12″(3.2mm)
+.06″(1.6mm)
O.D. of Hub <=12″ +.09″(2.4mm),
-.06″(1.6mm)
Diameter of
Contact Face
0.06″ Raised Face +/-.03″(0.8mm)
14″-42″ +/-.12″(3.2mm)
Diameter of Contact face 0.06″ Raised Face +/- .03″(0.8mm) Diameter of Hub at base X<=24″ +/-.06″(1.6mm)
X>24″ +/-.12″(3.2mm)
Deameter of Contact face <=10″ +.03″(0.8mm),
-0″
Diameter of Hub at point of Welding <=5″ +.09″(2.4mm),
-.03″(0.8mm)
12″-42″ +.06″(1.6mm),
-0″
>=6″ +.16″(4.0mm),
-.03″(0.8mm)
Drilling Bolt Circle 1/2“-24”
/26″-42″
Drilling Bolt Circle 1/2“-24”
/26″-42″
+/-.06″(1.6mm)
+/-.06″
+/-.06″(1.6mm)
+/-.06″
Bolt hole
spacing
+/-.03″(0.8mm) Bolt hole
spacing
+/-.03″(0.8mm)
Eccentricity of Bolt circle with respect to bore .03″ Max.
(0.8mm)
Eccentricity of Bolt circle with respect to bore .03″ Max.
(0.8mm)
Thickness 18″& Small +.12″(3.2mm),-0″ Thickness 18″& Small +.12″(3.2mm),-0″
20″-42″ +.19″(1.6mm) 20″-42″ +.19″(1.6mm)
Length Thru Hub <=10″ +/-.06″(1.6mm) Length Thru Hub <=10″ +/-.06″(1.6mm)
12″-42″ +/1.12″(3.2mm) 12″-42″ +/1.12″(3.2mm)

These tolerances are a part of ANSI B16.5 and AWWA C207-01 Sec. 4.2 except where noted otherwise.  The limits given are maximum.  Rigid inspection procedure assures the maintenance of high standards of accuracy in regular day to day production.

International standards of flanges

AWWA Standard Flange

AWWA C207

  • Steel Ring Flange: Class B, Class D, Class E, Class F
  • Steel Hub Flange: Class D, Class E
  • Blind Flange: Class B, Class D, Class E, Class F

AWWA C207

  • Steel Ring Flange: Class B, Class D, Class E, Class F
  • Steel Hub Flange: Class D, Class E
  • Blind Flange: Class B, Class D, Class E, Class F

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 B16.24 – Cast Copper Alloy Pipe Flanges and Flanged Fittings: Classes 150, 300, 600, 900, 1500, and 2500
  • 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 / A105M – Specification for Carbon Steel Forgings for Piping Applications

AWWA STANDARDS

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

MSS STANDARDS

  • 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-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).

Types of sealing faces

Different types of flange faces are used as the contact surfaces to seat the sealing gasket material.

The type of flange

The type of sealing face

 Pressure Class(PN,MPA)

 Plate flange(PL)

Raise Face(RF)

0.25-2.5

Flat Face( FF)

0.25-1.6

Slip on flange(SO)

Raise Face(RF)

0.6-4.0

Flat Face( FF)

0.6-1.6

male and female face (MFM)

1.0-4.0

Tongue and groove face (TG)

1.0-4.0

Welding Neck Flange(WN)

Raise Face(RF)

1.0-25.0

male and female face (MFM)

1.0-16.0

Tongue and groove face (TG)

1.0-16.0

 Ring Joint Face(RTJ)

6.3-25.0

Flat Face( FF)

1.0-1.6

Integral type flange(IF)

Raise Face(RF)

0.6-25.0

male and female face (MFM)

1.0-16.0

Tongue and groove face (TG)

1.0-16.0

 Ring Joint Face(RTJ)

6.3-25.0

Flat Face( FF)

0.6-1.6

Socket Weld Flange(SW)

Raise Face(RF)

1.0-10.0

male and female face (MFM)

1.0-10.0

Tongue and groove face (TG)

1.0-10.0

Thread Flange(Th)

Raise Face(RF)

0.6-4.0

Flat Face( FF)

0.6-1.6

Lap joint Flange(LP)

Raise Face(RF)

0.6-1.6

male and female face (MFM)

1.0-1.6

Tongue and groove face (TG)

1.0-1.6

Blind flange(BL)

Raise Face(RF)

0.25-25.0

male and female face (MFM)

1.0-16.0

Tongue and groove face (TG)

1.0-16.0

 Ring Joint Face(RTJ)

6.3-25.0

Flat Face( FF)

0.25-1.6

Raised Face (RF)

Raised Face - What are Steel Flanges?

Raised FaceThe Raised Face flange is the most common type used in process plant applications, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face. This face type allows the use of a wide combination of gasket designs, including flat ring sheet types and metallic composites such as spiral wound and double jacketed types. The purpose of a RF flange is to concentrate more pressure on a smaller gasket area and thereby increase the pressure containment capability of the joint. Diameter and height are in ASME B16.5 defined, by pressure class and diameter. Pressure rating of the flange determines the height of the raised face.
The typical flange face finish for ASME B16.5 RF flanges is 125 to 250 µin Ra (3 to 6 µm Ra).

Raised Face height - What are Steel Flanges?

For the height measures H and B of all described dimensions of flanges on this website, with exception of the Lap Joint flange, it is important to understand and remember the following:
In pressure classes 150 and 300, the height of raised face is approximately 1.6 mm (1/16 inch). In these two pressure classes, almost all suppliers of flanges, show in their catalog or brochure, the H and B dimensions including the raised face height. (Fig. 1) 
In pressure classes 400, 600, 900, 1500 & 2500, the height of raised face is approximately 6.4 mm (1/4 inch). In these pressure classes, most suppliers show the H and B dimensions excluding the raised face height. (Fig. 2)

Flat Face (FF)

Flat Face - What are Steel Flanges?

The Flat Face flange has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.
Flat face flanges are never to be bolted to a raised face flange. ASME B31.1 says that when connecting flat face cast iron flanges to carbon steel flanges, the raised face on the carbon steel flange must be removed, and that a full face gasket is required.
This is to keep the thin, bittle cast iron flange from being sprung into the gap caused by the raised face of the carbon steel flange.

Ring-Type Joint (RTJ)

Ring Type Joint - What are Steel Flanges?

The Ring Type Joint flanges are typically used in high pressure (Class 600 and higher rating) and/or high temperature services above 800°F (427°C). They have grooves cut into their faces which steel ring gaskets. The 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.

Ring Type Joint gaskets are metallic sealing rings, suitable for high-pressure and high-temperature applications. They are always applied to special, accompanying flanges which ensure good, reliable sealing with the correct choice of profiles and material.
Ring Type Joint gaskets are designed to seal by “initial line contact” or wedging action between the mating flange and the gasket. By applying pressure on the seal interface through bolt force, the “softer” metal of the gasket flows into the microfine structure of the harder flange material, and creating a very tight and efficient seal.

Ring Type Joint gaskets - What are Steel Flanges?

The most applied rings are:

1. Type R-Oval according to ASME B16.20

The original style of metallic ring joint. Used on round bottomed groove flanges though can also be used on later, flat-bottomed groove flanges. Suitable for ASME B16.5 flanges from Class 150 to 2500.

2. Type R-Octagonal according to ASME B16.20

An improved design over the original Oval design. However these can be used only in flat-bottomed groove flanges. Suitable for ASME B16.5 flanges from Class 150 to 2500.

The octagonal cross section has a higher sealing efficiency than the oval and would be the preferred gasket. However, only the oval cross section can be used in the old type round bottom groove. The newer flat bottom groove design will accept either the oval or the octagonal cross section.
The sealing surfaces on the ring joint grooves must be smoothly finished to 63 Microinches and be free of objectionable ridges, tool or chatter marks. They seal by an initial line contact or a wedging action as the compressive forces are applied. The hardness of the ring should always be less than the hardness of the flanges.
Style R ring type joints are designed to seal pressure up to 6,250 psi in accordance with ASME B16.5 pressure ratings and up to 5,000 psi.

Male-and-Female (M&F)

Male and Female - What are Steel Flanges?

With this type the flanges also must be matched. One flange face has an area that extends beyond the normal flange face (Male). The other flange or mating flange has a matching depression (Female) machined into it’s face.
The female face is 3/16-inch deep, the male face is1/4-inch high, and both are smooth finished. The outer diameter of the female face acts to locate and retain the gasket. Custom male and female facings are commonly found on the Heat Exchanger shell to channel and cover flanges.
Depth of female (recessed) face normally equal to or less than height of male (raised) face, to prevent metal-to-metal contact during gasket compression Recessed O.D. normally is not more than 1/16″ larger than the O.D. of the male face Joint must be pried apart for disassembly

Tongue-and-Groove (T&G)

Tongue and Groove - What are Steel Flanges?

The Tongue and Groove faces of this flanges must be matched. One flange face has a raised ring (Tongue) machined onto the flange face while the mating flange has a matching depression (Groove) machined into it’s face.
Tongue-and-groove facings are standardized in both large and small types. They differ from male-and-female in that the inside diameters of the tongue-and-groove do not extend into the flange base, thus retaining the gasket on its inner and outer diameter. These are commonly found on pump covers and Valve Bonnets.
Tongue-and-groove joints also have an advantage in that they are self-aligning and act as a reservoir for the adhesive. The scarf joint keeps the axis of loading in line with the joint and does not require a major machining operation.
General flange faces such as the RTJ, T&G and the F&M shall never be bolted together. The reason for this is that the contact surfaces do not match and there is no gasket that has one type on one side and another type on the other side.

Groove to Flat

Groove to Flat - What are Steel Flanges?

  • One flange face is flat, the other is recessed
  • For applications requiring accurate control of gasket compression
  • Only resilient gaskets are recommended —spiral wound, hollow metal O-ring, pressure-actuated, and metal-jacketed gaskets

Advantages and disadvantages of T&G and M&F flange faces

Advantages:

Better sealing properties, more precise location and exact compression af sealing material, utilization of other, more suitable sealing and spezialized sealing material (O-rings). 

Disadvantages: 

Commercial availabillity and cost. Normal raised faced is far more common and ready available both regarding Valves, flanges and sealing material. Another complexity is that some rigid rules must be applied to the piping design. Do you order Valves to be female end both sides, or on one side maybe, in which case do you point all male ends in the flow direction, or what. Same applies to any flanged joint / vessel connection of course.

What is the difference between a RTJ, FF, and RF flange on seals and thermowells?

The raised face, RF, is the standard process connection on our third party seals and thermowells. Both have options for a RTJ and FF type flange connections. The Raised Face (RF) is the most common type used in process plant applications. 
The gasket surface of the flange is raised above the bolting circle face. A Ring-type Joint (RTJ) can also have a raised gasket face with the difference being the ring groove machined in this face.
This groove will accommodate a steel ring gasket for flange mating. The Flat Face, FF, flange has a gasket surface that is in the same plane as the bolting circle face. 
None of these three flange types are interchangeable between types, i.e. RTJ flange cannot be mated to a RF flange.

Serration on the Flange Face

The flange face has small grooves as you can see in the image. This machining is known as a serration. Flange face can be smooth or serrated type. Which type of face to use is depends on the type of the gasket and service of the fluid.

Serration on the Flange Face - What are Steel Flanges?

Smooth finish is used with metallic gasket whereas serrated finish is used with non-metallic gasket. Soft material of gaskets is set in this serration and prevent liquid or gas from passing from flange joint.

Yaang can be spiral or concentric rings as you can see in the slide. Concentric rings type finishing is used when fluid is of very low density. If you use spiral type finish with very low density fluid, it may find leakage path through the spiral cavity.

Serration of flange face is specified in RMS (Root Mean Square) or AARH (Arithmetic Average Rough Height), the most common value of serrated face is 120-250 AARH. Comparator gauge is used to check serration of the flange. In the image, you can see the how gauge is used to verify the value of serration.

The most used Surfaces

A serrated finish, either concentric or spiral, is required with 30 to 55 grooves per inch and a resultant roughness between 125 and 500 microinches.

Flange Face design - What are Steel Flanges?

This allows for various grades of surface finish to be made available by flange manufactures for the gasket contact surface of metal flanges. These grades are often referred to by name e.g. stock finish. The exact definition of each grade may differ between manufacturers, but can be generalised as follows;
The most used Surfaces - What are Steel Flanges?
Stock Finish
The gasket contact surface is typically formed by a continuous (sometimes called phonographic) spiral groove generated by a 1.6mm radius round-nosed tool at a feed rate of 0.8mm per revolution with a depth of 0.15mm. This will result in a roughness between Ra 3.2 and 12.5 micrometers (125 – 500 microinch).
Smooth Finish

No definite tool marking should be apparent to the naked eye. This is typically achieved by having the gasket contact surface formed by a continuous (sometimes called phonographic) spiral groove generated by a 0.8mm radius round-nosed tool at a feed rate of 0.3mm per revolution with a depth of 0.05mm. This will result in a roughness between Ra 3.2 and 6.3 micrometers (125 – 250 microinch).
Hydrogen Service Finish
The finish for flanges in hydrogen service is very smooth, typically between Ra 2 and 3.2 micrometers (79 – 125 microinch).
Cold Water Finish
The flange face appears as mirror like. This flange finish is usually expected to be used with metal to metal contact, i.e. without a gasket. It is seldom used in the oil, petrochem and related industries.
Measuring Surface Roughness
Flange finish is generally measured by visual and tactile means. Comparing the feel of the machined face with that of a surface finish comparator gauge, occasionally referred to as a Rupert gauge, is considered adequate.
There are two common methods of expressing roughness. They are the Arithmetic Average Roughness Height (AARH) and the Root Mean Square (RMS) Average.
Arithmetic Average Roughness Height- Calculation of the Arithmetic Average Roughness Height involves measuring the distance of the peaks and valleys and performing an arithmetic average of the measurements.
Root Mean Square Average – Calculation of the Root Mean Square Average involves measuring the distance of peaks and valleys, adding the square of these measurements and calculating the square root of the total.
The RMS value is approximately 11% higher than the AARH value.

Pressure Classes of Flanges

The Pressure Class or Rating for flanges will be given in pounds. Different names are used to indicate a Pressure Class.

Forged steel flanges, according to ASME B16.5, are made in seven primary Pressure Classes:

150, 30040060090015002500.

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.

Example of Pressure Rating

Flanges can withstand different pressures at different temperatures. As temperature increases, the pressure rating of the flange decreases. For example, a Class 150 flange is rated to approximately 270 PSIG at ambient conditions, 180 PSIG at approximately 400°F, 150 PSIG at approximately 600°F, and 75 PSIG at approximately 800°F.
In other words, when the pressure goes down, the temperature goes up and vice versa. Additional factors are that flanges can be constructed from different materials, such as stainless steel, cast and ductile iron, carbon steel etc.. Each material have different pressure ratings.
Below an example of a flange NPS 12 with the several pressure classes. As you can see, inner diameter and diameter of the raised face at all the same; but outside diameter, bolt circle and diameter of bolt holes become larger in each higher pressure class.

The number and diameters (mm) of the bolt holes are:

CL 150 – 12 x 25.4 CL 300 – 16 x 28.6 CL 400 – 16 x 34.9 CL 600 – 20 x 34.9
CL 900 – 20 x 38.1 CL 1500 – 16 x 54 CL 2500 – 12 x 73

flg pressure classes - What are Steel Flanges?

Pressure-Temperature Ratings – Example

Pressure-temperature ratings are maximum allowable working gage pressures in bar units at the temperatures in degrees celsius. For intermediate temperatures, linear interpolation is permitted. Interpolation between class designations is not permitted.
Pressure-temperature ratings apply to flanged joints that conform to the limitations on bolting and on gaskets, which are made up in accordance with good practice for alignment and assembly. Use of these ratings for flanged joints not conforming to these limitations is the responsibility of the user.
The temperature shown for a corresponding pressure rating is the temperature of the pressure-containing shell of the component. In general, this temperature is the same as that of the contained fluid. Use of a pressure rating corresponding to a temperature other than that of the contained fluid is the responsibility of the user, subject to the requirements of applicable codes and regulations. For any temperature below -29°C, the rating shall be no greater than the rating shown for -29°C.
As an example, below you will find two tables with material groups acc. to ASTM, and two other tables
with flange pressure-temperature ratings for those ASTM materials acc. to ASME B16.5.

Requirements are valid for normal situation, in special you have to contact us to introduce.

ASTM GROUP 2-1.1 MATERIALS

Nominal
Designation
Forgings Castings Plates
C-Si A105(1) A216
Gr.WCB (1)
A515
Gr.70 (1)
C Mn Si A350
Gr.LF2 (1)
A516
Gr.70 (1), (2)
C Mn Si V A350
Gr.LF6 Cl 1 (3)
A537
Cl.1 (4)
3.1/2Ni A350
Gr.LF3

Notes:

  • (1) Upon prolonged exposure to temperatures above 425°C, the carbide phase of steel may be converted to graphite. Permissible but not recommended for prolonged use above 425°C.
  • (2) Do not use over 455°C.
  • (3) Do not use over 260°C.
  • (4) Do not use over 370°C.

ASTM GROUP 2-2.3 MATERIALS

Nominal
Designation
Forgings Cast Plates
16Cr 12Ni 2Mo A182
Gr.F316L
A240
Gr.316L
18Cr 13Ni 3Mo A182
Gr.F317L
18Cr 8Ni A182
Gr.F304L (1)
A240
Gr.304L (1)

Note: Do not use over 425°C.

PRESSURE-TEMPERATURE RATINGS FOR ASTM GROUP 2-1.1 MATERIALS

Working pressure by Classes, BAR

TEMP(°C) 150 300 400 600 900 1500 2500
-29 TO 38 19.6 51.1 68.1 102.1 153.2 255.3 425.5
50 19.2 50.1 66.8 100.2 150.4 250.6 417.7
100 17.7 46.6 62.1 93.2 139.8 233 388.3
150 15.8 45.1 60.1 90.2 135.2 225.4 375.6
200 13.8 43.8 58.4 87.6 131.4 219 365
250 12.1 41.9 55.9 83.9 125.8 209.7 349.5
300 10.2 39.8 53.1 79.6 119.5 199.1 331.8
325 9.3 38.7 51.6 77.4 116.1 193.6 322.6
350 8.4 37.6 50.1 75.1 112.7 187.8 313
375 7.4 36.4 48.5 72.7 109.1 181.8 303.1
400 6.5 34.7 46.3 69.4 104.2 173.6 289.3
425 5.5 28.8 38.4 57.5 86.3 143.8 239.7
450 4.6 23 30.7 46 69 115 191.7
475 3.7 17.4 23.2 34.9 52.3 87.2 145.3
500 2.8 11.8 15.7 23.5 35.3 58.8 97.9
538 1.4 5.9 7.9 11.8 17.7 29.5 49.2
TEMP (°C) 150 300 400 600 900 1500 2500

PRESSURE-TEMPERATURE RATINGS FOR ASTM GROUP 2-2.3 MATERIALS

Working pressure by Classes, BAR

TEMP(°C) 150 300 400 600 900 1500 2500
-29 TO 38 15.9 41.4 55.2 82.7 124.1 206.8 344.7
50 15.3 40 53.4 80 120.1 200.1 333.5
100 13.3 34.8 46.4 69.6 104.4 173.9 289.9
150 12 31.4 41.9 62.8 94.2 157 261.6
200 11.2 29.2 38.9 58.3 87.5 145.8 243
250 10.5 27.5 36.6 54.9 82.4 137.3 228.9
300 10 26.1 34.8 52.1 78.2 130.3 217.2
325 9.3 25.5 34 51 76.4 127.4 212.3
350 8.4 25.1 33.4 50.1 75.2 125.4 208.9
375 7.4 24.8 33 49.5 74.3 123.8 206.3
400 6.5 24.3 32.4 48.6 72.9 121.5 202.5
425 5.5 23.9 31.8 47.7 71.6 119.3 198.8
450 4.6 23.4 31.2 46.8 70.2 117.1 195.1
TEMP(°C) 150 300 400 600 900 1500 2500

Applications of flanges

Flanges are integral parts of many engineering and plumbing projects. In many applications, engineers need to find a way to close off a chamber or cylinder in a very secure fashion, usually because the substance inside must differ from the substance outside in composition or pressure. They do this by fastening two pieces of metal or other material together with a circle of bolts on a lip. This “lip” is a flange.

Plumbing

You can connect two sections of metal piping by soldering or welding them together, but pipes connected in this way are very susceptible to bursting at high pressures. A way of connecting two sections of pipe more securely is by having flanged ends that you can connect with bolts. This way, even if gases or liquids build up to high pressures inside the pipe, it will often hold with no problem.

Mechanics

In order to connect two sections of a large, enclosed area, it is often best to used flanges and bolts. An example of this is the connection between the engine and the transmission in an automobile. In this case, both the engine and the transmission contain a number of moving parts that can easily get damaged if they get dust or other small objects inside of them. By connecting the outer casings of the engine and transmission in this way, engineers protect the inner workings of both.

Electronics

Flanges have a specific purpose in cameras and other electronic devices. Though flanges in such items do not usually have to sustain high pressures, they do have to hold tight so they can keep out harmful particles. These flanges are usually found connecting two different materials, such as the glass of a lens and the rest of the body of the camera.

Applications of ANSI Long Weld Neck Flanges

Applications involving high pressure and the need for a hub that is long and tapered are what weld neck flanges are most often used for. Specifying the schedule of pipe that it will be utilized for is of utmost importance when ordering. This type of flange is excellent for use in environments involving extreme temperature fluctuations and excessive handling and bending.

Uses for Long Weld Neck Flanges

The uses for long weld neck flanges are predominantly on vessels where an extended neck is required. The uses for long weld neck flanges (LWN) are predominantly on vessels where an extended neck is required. This is deemed to be a specialty flange due to the protruding neck or hub, which acts as a boring extension.

The tapered neck aids in reducing the thickness of the steel and it then seems to be a pipe extension. Steel LWN flanges are chiefly utilized in the chemical and petroleum industries, as well as commercial and residential buildings that experience high levels of stress and temperatures that fluctuate.

Application of Spectacle blinds

Spectacle Blinds are generally applied to permanently separating pipesystems, or just to connect with each other. A Spectacle Blind is a steel plate cut into two discs of a certain thickness.

SPECTACLE BLIND IN OPEN POSITION

spectacle open - What are Steel Flanges?

SPECTACLE BLIND IN CLOSED POSITION

spectacle closed - What are Steel Flanges?

What is the use of a blind flange?

Blind flange is put at the end of pipe or at the junction that would possibly be a future expansion into that direction.

BLIND FLANGE IN CREATE A STOP

blind flange usage close the end of pipe - What are Steel Flanges?

BLIND FLANGE IN BLOCK OFF A PIPELINE

blind flange usage block off a pipeline - What are Steel Flanges?

A blind flange is a round plate which has all of the relevant blowholes except center hole, and because of this feature the blind flange is usually used to close off the ends of a piping systems and pressure vessel openings. It also permits easy access to the interior of a line or vessel once it has been sealed and must be reopened.
Often a blind flange is inserted into a pipeline when a repair is required further up the line. This allows the flanges down stream to be disconnected without fear of losing liquid. Many times this type of blockade is used when adding another line onto an existing pipeline or when a new valve is being added. This blockade is also used to shut down a line when it is no longer needed.

Materials for Flanges Based on Applications

Steel pipe flanges have a flat rib, collar or rim that is utilized for guiding or strengthening when attaching two pipes to each other. Materials, sizes and opening dimensions are varying based upon applications that the flanges are designed for and include threaded, socket-wired and slip-on styles.

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 - What are Steel Flanges?
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.

Connection Types of Flanges

Connection types of flanges can generally be divided into five kinds: flat welding, butt welding, socket welding, loose and threaded.

Flange Facing Types - What are Steel Flanges?

Flange easy to use, able to withstand greater pressure. Below is the detailed description of first four kinds:

  1. Flat welding: only for welding outer layer, welding inner layer is not required; normally, it often used in medium, low pressure pipes. Nominal pressure of pipe is lower than 2.5Mpa. Sealing surface of flat welding flanges has three kinds: smooth type, concave-convex type and tongue and groove type. Among them, smooth type is the most widely used with cost effective.
  2. Butt welding: both outer and inner of flange need to be welded. Normally, it is widely used in medium and high pressure pipes. Nominal pressure of pipe is between: 0.25-2.5Mpa. Seal surface of connection type of butt welding flange is concave-convex type with complex installation. Therefore, cost of labor, installation method and auxiliary is a little high.
  3. Socket welding: normally, it is used in the nominal pressure lower than 10.0 Mpa. Nominal diameter is lower or equal to 40mm of pipe.
  4. Loose: normally used in the pipes with not high and its medium is a little corrosive. Therefore, this kinds of flange is corrosion resistant. The material is mainly stainless steel.

Allowable size of flange sealing surface defects Unit: mm

Nominal size DN Maximum radial projection size of defect (defect depth ≤ h) Maximum depth and radial projection size of defect (defect depth > H)
15 3.0 1.5
20 3.0 1.5
25 3.0 1.5
32 3.0 1.5
40 3.0 1.5
50 3.0 1.5
65 3.0 1.5
80 4.5 3.0
100 6.0 3.0
125 6.0 3.0
150 6.0 3.0
200 8.0 4.5
250 8.0 4.5
300 8.0 4.5
350 12.0 4.5
400 12.0 4.5
450 12.0 6.0
500 12.0 6.0
600 12.0 6.0
700-900 12.5 6.0
1000-1400 14.0 7.0
1600-2000 15.5 7.5

Note:

  • 1. The radial projection dimension of the defect is the difference between the maximum radius and the minimum radius of the defect from the center of the flange hole.
  • 2. H is the serrated concentric circle or spiral groove depth of the flange sealing surface.

Flange installation

Flange is mainly used in pipeline installation. Flange connection is an important connection mode of pipeline construction. It mainly connects the connection between pipes and plays an important role and value. Flange connection is to fix two pipes, pipe fittings or equipment on a flange respectively, add flange pads between the two flanges, and fasten them together with bolts to complete the connection.
Some pipe fittings and equipment have their own flanges, which also belong to flange connection. Butt welding flange has a wide range of uses, and the scope of use is determined according to different characteristics. It is mostly used when the medium conditions are relatively mild, such as low-pressure non purified compressed air and low-pressure circulating water. Its advantage is that the price is relatively cheap.
Because the nominal diameter of the container barrel of the butt welding flange and the nominal diameter of the pipe represent different specific dimensions, the dimensions of the stainless steel flange and the stainless steel butt welding flange of the container with the same nominal diameter are also different, and they cannot be substituted for each other. In general, butt welding flanges are always processed by dividing them into several arc segments:
Butt welding flange is a kind of pipe fitting, which refers to the flange with neck and circular pipe transition and butt welded with the pipe. Butt welding flange is a kind of disc-shaped parts, which is common in pipeline engineering. Flanges are used in pairs. In pipeline engineering, butt welding flange is mainly used for pipeline connection.
Flanges with different pressures have different thicknesses and use different bolts. When pumps and valves are connected with pipes, parts of these equipment are also made into corresponding flange shapes, also known as flange connection. A flange plate shall be installed for various pipelines to be connected. Threaded flanges can be used for low-pressure pipelines, and welded flanges can be used for pressure above 4kg. A sealing point shall be added between the two flanges, and then fastened with bolts.
There are four main problems during flange installation:

  • 1. Offset – the pipeline is not vertical, concentric, and the flange is not parallel. When using non-metallic gasket, it shall be less than 2mm; Metal composite gaskets, elliptical gaskets and flanges connected with equipment shall be less than 1mm.
  • 2. Staggered hole – the pipeline flange is concentric, but the chord distance (or bolt hole center circle diameter, etc.) of the two flanges relative to the bolt hole diameter has a large deviation. The allowable deviation of chord distance of two adjacent bolt hole diameters is ± 0.5mm
  • 3. Opening – the allowable opening value between two flanges is graphite packing (excluding the pre stretching of pipeline and the thickness of gasket or blind plate), and the opening of pipe flange shall be less than 3mm; The flange connected with the equipment shall be less than 2mm.
  • 4. Staggered joint – the pipeline is perpendicular to the flange, but the two flanges are not concentric.
  • Under the condition of composite standard of bolt hole diameter and bolt diameter, it is qualified if the bolt is freely penetrated into the bolt hole without other tools.

Calculation method of theoretical weight of flange finished product

Theoretical weight algorithm of flange finished product:
(outer diameter * outer diameter – inner diameter * inner diameter – bolt hole diameter * bolt hole diameter * number of bolt holes) * thickness * 0.616 * 0.00001 = theoretical weight of finished flange. It can also be said to be the actual weight.
There will be a little difference between the positive and negative of the flange processed by the lathe and the actual weight of the flange. Therefore, we call it the theoretical weight. Generally, the theoretical weight is used to measure the standard of the flange in China.

Gross weight algorithm of flange

Calculation method of flange blank weight: outer diameter * outer diameter * 1234 * thickness – inner diameter * inner diameter * 1234 * thickness. In the calculation process, it should be noted that the weight of the upper blank is to be processed. Therefore, the standard of the finished product drawing should add 5 ~ 20mm according to the size. The price calculated by the blank weight is much more accurate and much cheaper than the theoretical weight of the finished product.

How to select the correct flange?

Pipe flange and its gasket and fastener are widely used in chemical engineering design. It is not only an essential part in piping design, pipe fittings and valves, but also an essential component in equipment and its parts (such as people, hand holes, liquid level meters and mirrors), but also widely used in thermal engineering, water supply and drainage, heating and ventilation, instruments and so on. So how should we choose it correctly?

Selection principle

Generally, HG/T 20592, HG/T 20606 ~ 20607, HG/T 20611 ~ 20614 (European system), HG/T 20615, HG/T 20623, HG/T 20627 ~ 20628 and HG/T 20630 ~ 20635 (American system) are preferred for the selection of pipe flanges, gaskets and fasteners.
The nominal pressure of the standard pipe flange is set by dividing the pressure borne by the pipe into some standard grades according to the requirements of the standard. Each grade (PN) represents the maximum allowable working pressure of the flange with a certain material and working temperature. The nominal pressure of the pipe flange (PN) Based on the set material yield strength of 225MPa, the maximum allowable working pressure P under different working temperatures is calculated. When the flange material and working temperature are different, the maximum allowable working pressure will decrease or increase. The calculation method of the maximum allowable working pressure P under different working temperatures is as follows:

  • p=PN × (design strength / 225)

The design strength shall take the following minimum values:
(1) When the working temperature is lower than the creep temperature of the material, take the yield strength of the material;
(2) 1.5 times of the maximum allowable stress of the material at creep temperature;
(3) If the design strength of the material is higher than 225MPa, 225MPa shall still be taken.
The selection principles of pipe flanges for pressure vessels are as follows:
(1) Threaded flange, plate flat welding flange, flat welding ring loose flange, neck flat welding flange and lined flange cover are not recommended for flammable, explosive, highly hazardous media.
(2) For medium with explosive or moderate toxicity, the nominal pressure of pipe flange shall not be less than 1MPa; for medium with high toxicity, extreme or strong permeability, the nominal pressure of connecting flange shall not be less than 1.6Mpa.
(3) When the vacuum degree of vacuum vessel is less than 600mmhg, the nominal pressure of pipe flange shall not be less than 0.6MPa; when the vacuum degree is 600 ~ 700mmhg, the nominal pressure of pipe flange shall not be less than 1MPa.
(4) High, extremely hazardous media and class III pressure vessels shall adopt neck butt welding flanges.
(5) The grade and technical requirements of flange forgings shall meet the requirements of corresponding standards refer to the previous article “how to determine the forging grade of pressure vessel?”
(6) Service conditions of commercial grade hexagon bolt:

  • a. PN≤1.6MPa;
  • b. Non violent circulation occasions;
  • c. Equipped with non gold chip cushion;
  • d. The medium is non flammable, explosive and toxic.

(7) Service conditions of commercial stud bolts and nuts:

  • a. PN≤4.0MPa;
  • b. Non violent circulation occasions.

(8) When using austenitic stainless steel flanges, the following provisions shall be met:

  • a. Austenitic stainless steel flange fasteners should be made of materials with similar linear expansion coefficient;
  • b. Ordinary austenitic stainless steel flange fasteners without cold work hardening, such as a2-50, are only applicable to non-metallic flat gaskets, PTFE coated gaskets and flexible graphite composite gaskets;
  • c. When the working temperature is not more than 230 ℃, ferritic steel (carbon steel or alloy structural steel) fasteners can be used;
  • d. Cold work hardened austenitic stainless steel flange fasteners, such as A2-70 and a4-70, can be applied to semi-metallic pads such as winding pads, metal clad pads, tooth shaped combination pads, etc.

The selection of pipe flange shall be comprehensively considered according to the design conditions. The above are some selection principles summarized. We shall strive to ensure that the selected structure is reasonable and the cost is the least.
Flange selection shall be determined according to flange parameters.
When using the flange, the flange size shall be determined first, and the nominal diameter and pressure of the flange shall be known before determining the flange size. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel shall take the same series of values; the determination of the flange nominal pressure is related to the maximum operating pressure, operating temperature and flange material of the flange, and the flange specified in the pressure vessel flange standard The materials are low carbon steel, ordinary low steel and stainless steel. Their nominal pressure and maximum allowable working pressure are different at different temperatures.
In addition to flat welding and butt welding flanges, pipe flanges also include cast steel flanges, cast iron flanges, looper flanges, threaded flanges, etc. in addition to national standards, pipe flange standards also include standards of the Ministry of chemical industry and Sinopec. Among them, the standards of the Ministry of chemical industry are divided into European system and American system, while those commonly used in China are European system. It is worth noting that the nominal value of container barrel is The specific dimensions represented by the diameter and the nominal diameter of the pipe are different. Therefore, the dimensions of the container flange and pipe flange with the same nominal diameter are also different, and they can not be substituted for each other.
The flange shall be selected according to the actual use.
For example, the groove surface or concave surface of the equipment flange of the vertical vessel shall be upward, and the groove surface or concave surface of the horizontal vessel shall be located on the cylinder. Therefore, we can choose the flat welding flange with neck. After all, it belongs to the national standard flange standard system. Its advantage is that it is convenient for on-site installation and can omit the process of weld damage. It is one of the commonly used flanges on the equipment or pipeline; it can also be selected With neck flat welding flange, its connection is not easy to deform, the sealing effect is good, and it is widely used. It is suitable for pipelines with large fluctuation of temperature or pressure or pipelines with high temperature, high pressure and low temperature. It is also used for pipelines conveying expensive media, flammable and explosive media and toxic gases.
In various domestic standards, the integral flange is represented by if, which is generally convex surface (RF). It is mostly used in pipelines with high pressure. If it is used under flammable, explosive, high and extremely hazardous working conditions, the sealing surface of convex concave surface (MFM) and tenon and groove surface (TG) other than RF surface can be selected.
When determining the flange size using the flange standard, you must know the nominal diameter and nominal pressure of the flange. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel take the same series of values. For example, dn1000mm pressure vessel should be equipped with dn1000mm pressure vessel flange.
The determination of flange nominal pressure is related to the maximum operating pressure, operating temperature and flange material of the flange. When formulating flange size series and calculating flange thickness, it is based on the mechanical performance of 16MnR at 200 ℃. Therefore, it is stipulated that the flange size determined based on this benchmark. At 200 ℃, its maximum allowable operating pressure is considered to be the flange with this size For example, a flange with a nominal pressure of pno.6mpa refers to a flange with such a specific size. The flange is made of 16MnR, and its maximum allowable operating pressure is 0.6MPa at 200 ℃. If the flange with a nominal pressure of pn0.6mpa is used at a temperature higher than 200 ℃, its maximum operating pressure will be lower than its nominal pressure of 0.6MPa. On the contrary, such as If it is used at a temperature lower than 200 ℃, the maximum working pressure is still determined at 200 ℃. If the flange material is changed to Q235-A, the mechanical properties of Q235-A steel are worse than 16MnR. Even if the flange with nominal pressure of pn0.6mpa is operated at 200 ℃, its maximum allowable operating pressure will be lower than its nominal pressure. On the contrary, if the flange material is changed from 16MnR to 15 Mnvr, since the mechanical performance of 15MnVR is better than 16MnR, the maximum allowable operating pressure of the flange with nominal pressure of pn0.6mpa will be higher than its nominal pressure when operating at 200 ℃. In short, as long as the nominal diameter and nominal pressure of the flange are determined, the size of the flange will be determined. As for the maximum allowable operating pressure of the flange, it depends on the flange The operating temperature and the material used.

Source: China Steel Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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