Description

Flanges are used to connect pipes with each other, to valves, to fittings, and to specialty items such as strainers and pressure vessels. There are instances where the design may require dissimilar metals or different classifications are required to be bolted together. When this happens, be sure to seek engineering advise to ensure that the design is still within compliance with the applicable standards and specifications.

Flange, abbreviated as FLG, is a bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system. Flanges provide access for when equipment (or piping) needs to be cleaned, inspected or reconfigured. A flange pair is made up of two flanges and a gasket with bolts and nuts. Pipe flanges come in different styles, pressure ratings, materials and sizes to meet the design requirements. In the oil field, the two most commonly used flange standards are ANSI/ASME B16.5 and BS 1560. API Spec 6A is for flanges used on wellhead and christmas tree equipment.

Flanges types

Flanges mostly come in six different types. However, these designs can be modified to meet the specific functions and requirements of the applications. Therefore, it’s essential to understand the pressure at the flagged joint, the required strength, and the size of pipes involved. With the correct information comes six types of flanges that an individual can choose from. These include:

Blind Flange – These flanges do not have a bore. It is used to blind off a flange or even a valve. When used at the end of a pipe or fitting, it provides an easy to open access for further extension of the pipe. The blind flange and its bolts are stressed more than any other flange.

Lap Joint Flange – This flange is used with a lap joint stub end fitting. It is similar to a slip-on flange, but with two differences. The radius and the flat face, both allow the flange to secure against the stub end fitting. This is useful where alignment of bolt holes is difficult, such as with spools to be attached to flanged nozzles of vessels. A lap joint is used in low pressure applications and not suitable where high external of heavy loads are present.

Slip-on Flange – Slip-on flanges are designed to slip over the outside of pipe, long-tangent elbows, reducers, and swages. The flange has poor resistance to shock and vibration. It is easier to align than a weld neck flange. This flange is ideal for low pressure applications since the strength when under internal pressure is about one third that of a weld neck flange.

Socket Weld Flange – This is similar to a slip-on flange, except they have a bored and counter bore. The counter bore allows the pipe to fit into the socket/counter bore. The bore of the flange is the same diameter as the inside of the pipe. These flanges were first designed for small diameter, high pressure pipe.

Threaded Flange – It is similar to a slip-on Flange, but has internal threads. It is normally used for low pressure and not used where temperature or stress is very high.

Weld Neck Flange – This flange comes in two types, regular and long. The hub of the weld neck is designed to reduce the stress at the base of the flange. Regular weld neck flanges are used with buttweld fittings and long weld neck flanges are usually used with equipment and vessel nozzles. A long weld neck flange is rarely used with pipe. Both types of flanges are bored to match the inside diameter of the pipe or fitting to which it will be welded to. They are suitable where high pressure, extreme temperatures, shear impact and vibratory stresses apply.

There are also a number of specialty flange types

Additionally, the flanges can be modified to form other types, depending on application and functions. These unique designs are made to incorporate specific needs and applications, like reducing flanges to answer to size and orifice flanges to incorporate orifice mounting. Other examples in this category include:

Orifice Flange – Orifice flanges are for metering the volumetric flow rate of liquids and gasses through a pipe. This flange is normally available in weld neck, slip-on, and threaded flanges.

Standard Connection Flange – This flange is normally used for nozzles on pressure vessels and rarely used with pipe.

Expander Flange – An expander flange is similar to a weld neck flange but with the hub expanding to a larger size (one or two sizes).

Reducing Flange – Reducing flanges are designed for when there is a change in the pipe size.

Studding Outlet Flange: Flat Bottom Mount – Shell/Head Mount – Tangential Mount – These flanges have shaped welded ends to match a tank or vessel.

Weldoflange / Nipoflange – A weldoflange is an olet connection, it is simular to a nipoflange, both are used for a branch connection on a pipe.

The 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.

A flanged joint comprises three components; flanges, gaskets, and bolting and assembled by pipefitter. Special controls are required to select and apply all these elements to attain a joint, which has acceptable leak tightness.

 

Categorizing pipe flanges

The most common way of classifying flanges is by considering their shapes. However, it’s essential to understand that there are other ways to categorize flanges, as these come in handy when durability, functionality, and application are in question. These include:

• Classification by material used includes brass, alloy steel, cast iron, carbon steel, stainless steel, aluminum, or PVC.
• Classification by flange face includes flat, ring joint, raised, female and male, lap joint, tongue, and groove.
• Classification by piping flange dimensions, which include pressure rating or nominal size.
• Classification by flange finish, which gives smooth, stock, or serrated.

Pipe flange standards

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).

Pipe flange classes

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.

Pipe flange facing

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:

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.

Faqs

How flanges operate

Flanges have flat or flush surfaces that are vertical to the pipe to which they are attached. The attachment process involves mechanically joining two or more faces using bolts, adhesives, collars, or welds.

Due to the attachment requirements, a flange must fit the equipment or pipe that it’s designed. That’s why it’s necessary to check all the possible specifications and dimensions to ascertain that it’s of the right size, type, and material.

What are the three parts of a flanged connection?

Pipe flanges, gaskets, and bolts are the three parts that comprise a flanged connection. Gaskets and bolts are typically made of the same flange materials or a material approved for the pipe components. Each component comes in various materials that suit specific applications and must be matched correctly for proper functioning.

The gaskets come in two conventional types: full-face gaskets and ring gaskets. Full-face gaskets have the bolt holes visible and pair up with raised-face gaskets. Ring gaskets tend to be smaller rings minus the bolt holes and pair up with flat-faced flanges.

Securing the flange components requires matching the surfaces evenly and plumb, adjusting as needed for a uniform fit. Once all surfaces match, bring the flanges together and secure at least two of the bolts. Refine the alignment, so the remaining bolt holes match and their corresponding bolts are tightly secured.

How do I properly size a flange for pipe use?

Properly sizing a flange for pipe use depends not only on the type of flange but its compatible piping. The pipe must slip into the flange’s inside diameter easily and securely, and the outside diameter should cover wall holes. Once you determine the specific flange type and material you need for the job, you’ll need to take several measurements.

The four measurements you’ll need are the inside diameter, outside diameter, bolt hole count, and bolt hole center. You’ll need to align each of these measurements from opposing bolt holes to get the most accurate readings. Take all measurements from edge to edge and try to get as precise as possible to match the correct product.

Round up bolt diameter to the next half or whole step since bolts measure half or whole inches. Once you have all four measurements, check them against the manufacturer’s table to find the correct flange. Most manufacturers list these specifications on their websites for easy reference.

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.

General pipe flange standards

• Flange – ASME B16.36, Orifice Flange (1/2″-24″)
  • Slip-on Flange: Class 300, Class 400, Class 600, Class 900, Class 1500
  • Threaded Flange: Class 300, Class 400, Class 600, Class 900, Class 1500
  • Weld Neck Flange: Class 300, Class 400, Class 600, Class 900, Class 1500, Class 2500

• Flange – Industry Standard Flange (also called Large Diameter Flange) (26″-larger)
  • Industry Standard Flanges have no national standard code or are they covered by any governing body.
    • Blind Flange: Class 75, Class 125, Class 175, Class 250, Class 350
    • Weld Neck Flange: Class 75, Class 125LW, Class 125, Class 175, Class 250, Class 350
    • Slip-on Flange: Class 75, Class 125LW, Class 125, Class 175, Class 250, Class 350

• Flange – 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

Flange pressure classes

Flanges are normally manufactured in seven basic ratings: 150 Lb, 300 Lb, 400 Lb, 600 Lb, 900 Lb, 1500 Lb and 2500 Lb. The ratings can be expressed in different ways but mean the same thing – 150 Lb, 150 Lbs, 150# or Class 150.

Each class of flange can handle more pressure than the previous class because of its construction. The higher the class is, the thicker the metal is. Thus a higher pressure can be handled. There a numerous factors that can affect the pressure capability of a flange, such as the type of metal that is used.

Flange specification, BSI

The BSI specifications for flanges are:

• BS 10 – Specification for Flanges and Bolting for Pipes, Valves, and Fittings
• BS 3293 – Specification for Carbon Steel Pipe Flanges (over 24 inches nominal size) for the Petroleum Industry
• BS 4504 – Specification for Steel Flanges Circular Flanges for Pipes, Valves and Fittings
• ISO 7005-1 – Metallic Flanges – Part 1: Steel Flanges (this is substantially the same as BS 4504)

BSI flange materials

Standards usually specify the material from which the flange is produced.

BSI flange sizes

There are available flange sizes and grades for all standard pipe wall thicknesses and pressure ratings.

BSI flange facing types

The typical flange faces used are flat face, raised face, tongue and groove and ring joint.

BSI flange finish

The flange face finish is determined by the standard used and measured as an Arithmetical Average Roughness Height (AARH).  An example would be ANSI B16.5 which specifies face finishes within a range 125AARH – 500AARH (3.2 Ra to 12.5 Ra).

Flange Materials

Flanges are welded to pipe and equipment nozzle. Accordingly, it is manufactured from the following materials;

• Carbon steel
• Low alloy steel
• Stainless steel
• Combination of Exotic materials (Stub) and other backing materials

The list of materials used in manufacturing 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”

Commonly used Forged material grads are

• Carbon Steel: – ASTM A105, ASTM A350 LF1/2, ASTM A181
• Alloy Steel: – ASTM A182F1 /F2 /F5 /F7 /F9 /F11 /F12 /F22
• Stainless Steel: – ASTM A182F6 /F304 /F304L /F316 /F316L/ F321/F347/F348

Marking on the Flanges Body

Each piping component is marked for proper identification. Marking of flanges must include the following so that during fabrication and post-fabrication it can be easily traced;

• 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)

Applications of flanges

When a piping joint requires to be dismantled, flanges are being used. These are primarily used on equipment, valves, and specialty items. Breakout flanges are provided at predetermined intervals in certain pipelines where maintenance is a regular occurrence. The flanges, gaskets, and bolting make up a flanged joint, which is made up of three separate but interconnected components. To achieve a leak-proof joint, special controls are required in the selection and application of all of these elements.

Here are the details of Flanges about their advantages and their applications.

Advantages of Flanges

Pipes, valves, pumps, and other parts are connected with flanges to form a piping system. Generally, flanges are welded or screwed together. The use of flanges makes pipe system maintenance and repair a breeze. Instead of taking the entire pipe for inspection, a small section of the pipe can be carefully investigated to use a flange to locate the fault.

The following are the five most important benefits of The following are the five most important benefits of flanges:

• Easy assembly in tight spaces where wrenches may not have clearance if traditional flange fittings are used. With moderate torque, they’re easier to put together.
• In hard-to-reach areas where flexibility is required, adapters in the hose line, pipe, or tube can be removed.
• Pipe connections, tubes, or large hose links with high pressure, vibration, or shock pressures that could damage traditional large hydraulic fittings more easily.
• In rigid lines such as metal tubes or continuous pipes, making connections allows for easy maintenance.
• In demanding hydraulic applications, reduce the chance of components becoming loose.

A flange is a method of connecting pipes, valves, pumps, and other equipment to form a piping system. It also provides easy access for cleaning, inspection, or modification. Flanges are usually welded or screwed.

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.