ASME /ANSI FLANGES
flange is used to join pipe, valves, or a vessel within a system.The internal environment outlines the design and operating conditions of temperature, pressure, and fluid. With the external environment, consideration is given to location of the flange, whether it is operating in air or sub-sea, and externally applied piping loads.
An understanding of the environment is crucial to the design and selection of the appropriate components with the correct assembly methods.The components include the most appropriately designed and selected flange, gasket, and bolting, commensurate with the risk dictated by the environment.
Assembly includes checking the condition of the components and proceeding according to established procedures. Proper assembly requires that
Flange faces meet the standards
● Gasket-seating stress is achieved
● Bolts, nuts, and gaskets are free of defects
● Appropriate lubrication is used
Flange Standards
There are a variety of standards used in the design and selection of flanges. The
ASME codes and standards relate to pipe flanges:
ASME Codes and Standards:
B16.1 Cast Iron Flanges and Flanged Fittings
B16.5 Pipe Flanges and Flanged Fittings
B16.24 Bronze Flanges and Fittings–150 and 300 Classes
B16.42 Ductile Iron Pipe Flanges and Flanged Fittings–150 and 300 Classes
B16.47 Large Diameter Steel Flanges
Section VIII
Division 1 Pressure Vessels
Appendix 3 Mandatory Rules for Bolted Flange Connections
Pressure ratings for flanges are designed to ANSI standards of 150 Ib, 300 Ib, 400 Ib, 600 Ib, 900 Ib, 1500 Ib, and 2500 lb.
The most common terminology used is the pound reference, although the more formal reference
is by class, such as Class 150 flange.
There are numerous types of flanges available. The type and material of flanges is dependent on the service environment:
Flange-End Connection
The flange-end connection defines the way in which it is attached to the pipe. The following are commonly available standard flange end types:
Weld-Neck (WN) Flange.
Weld-neck flanges are distinguished from other types by their long, tapered hub and gentle transition to the region where the WN flange is butt-welded to the pipe. The long, tapered hub provides an important reinforcement of the flange, increasing its strength and resistance to dishing. WN
Weld-neck flanges are distinguished from other types by their long, tapered hub and gentle transition to the region where the WN flange is butt-welded to the pipe. The long, tapered hub provides an important reinforcement of the flange, increasing its strength and resistance to dishing. WN
flanges are typically used on arduous duties involving high pressures or hazardous fluids.
The butt-weld may be examined by radiography or ultrasonic inspection. Usually, the butt-welds are subject to visual, surface, or volumetric examinations, or a combination thereof, depending on the requirements of the code of construction for piping or a component. There is, therefore, a high degree of reliability in the integrity of the weld. A butt-weld also has good fatigue performance, and its
presence does not induce high local stresses in the pipework.
Socket-Weld (SW) Flange.
Socket-weld flanges are often used on hazardous duties involving high pressure but are limited to a nominal pipe size NPS 2 (DN 50) and smaller. The pipe is fillet-welded to the hub of the SW flange. Radiography is not practical on the fillet weld; therefore correct fitting and welding is crucial. The fillet weld may be inspected by surface examination, magnetic particle (MP), or liquid penetrant (PT) examination methods.
Socket-weld flanges are often used on hazardous duties involving high pressure but are limited to a nominal pipe size NPS 2 (DN 50) and smaller. The pipe is fillet-welded to the hub of the SW flange. Radiography is not practical on the fillet weld; therefore correct fitting and welding is crucial. The fillet weld may be inspected by surface examination, magnetic particle (MP), or liquid penetrant (PT) examination methods.
Slip-on Flanges.
Slip-on flanges are preferred to weld-neck flanges by many users because of their initial low cost and ease of installation. Their calculated strength under internal pressure is about two-thirds of that of weld-neck flanges. They are typically used on low-pressure, low-hazard services such as fire water, cooling water, and other services. The pipe is ‘‘double-welded’’ to both the hub and the bore of
Slip-on flanges are preferred to weld-neck flanges by many users because of their initial low cost and ease of installation. Their calculated strength under internal pressure is about two-thirds of that of weld-neck flanges. They are typically used on low-pressure, low-hazard services such as fire water, cooling water, and other services. The pipe is ‘‘double-welded’’ to both the hub and the bore of
the flange, but, again, radiography is not practical. MP, PT, or visual examination is used to check the integrity of the weld. When specified, the slip-on flanges are used on pipe sizes greater than NPS 2¹⁄₂ (DN 65).
Composite Lap-Joint Flange.
This type of flanged joint is typically found on high alloy pipe work. It is composed of a hub, or ‘‘stub end,’’ welded to the pipe and a backing flange, or lapped flange, which is used to bolt the joint together. An alloy hub with a galvanized steel backing flange is cheaper than a complete alloy flange.
This type of flanged joint is typically found on high alloy pipe work. It is composed of a hub, or ‘‘stub end,’’ welded to the pipe and a backing flange, or lapped flange, which is used to bolt the joint together. An alloy hub with a galvanized steel backing flange is cheaper than a complete alloy flange.
The flange has a raised face, and sealing is achieved with a flat ring gasket.
Swivel-Ring Flange.
As with the composite lap-joint flange, a hub will be buttwelded to the pipe. A swivel ring sits over the hub and allows the joint to be bolted together. Swivel-ring flanges are normally found on sub–sea services where the swivel ring facilitates flange alignment. The flange is then sealed using a ring-type
As with the composite lap-joint flange, a hub will be buttwelded to the pipe. A swivel ring sits over the hub and allows the joint to be bolted together. Swivel-ring flanges are normally found on sub–sea services where the swivel ring facilitates flange alignment. The flange is then sealed using a ring-type
joint (RTJ) metal gasket.
Blind Flange.
Blind flanges are used to blank off the ends of piping, valves, and pressure vessel openings. From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed of all the standard flanges. However, since the maximum stresses in a blind flange are bending stresses at the center, they can be safely permitted to be stressed more than other
Blind flanges are used to blank off the ends of piping, valves, and pressure vessel openings. From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed of all the standard flanges. However, since the maximum stresses in a blind flange are bending stresses at the center, they can be safely permitted to be stressed more than other
types of flanges.
Threaded Flange
is used in systemsnot involving temperature or stresses of any magnitude.
Reducing Flange
The reducing flange is similar in every respect to the full size of the flange from which the reduction is to be made.
Long Weldneck Flange
This is a special flange used for nozzles on pressure vessels. The hub is always straight, and the hub thickness is greater than the diameter of any piping that may be bolted to the flange
Orifice Flange
The function of an orifice flange is to meter the flow of liquids and gases through a pipe line.
Flange Faces
There are five types of flange faces commonly found. The surface finish of the faces are specified in the flange standards quoted above.
Raised Face (RF).
The raised face is the most common facing employed with bronze, ductile iron, and steel flanges. The RF is ¹⁄₁₆-in high for Class 150 and Class 300 flanges and ¹⁄₄-in high for all pressure classes, higher than Class 300. The facing on a RF flange has a concentric or phonographic groove with a controlled surface finish. Sealing is achieved by compressing a flat, soft, or semimetallic gasket between mating flanges in contact with the raised face portion of the flange.
The raised face is the most common facing employed with bronze, ductile iron, and steel flanges. The RF is ¹⁄₁₆-in high for Class 150 and Class 300 flanges and ¹⁄₄-in high for all pressure classes, higher than Class 300. The facing on a RF flange has a concentric or phonographic groove with a controlled surface finish. Sealing is achieved by compressing a flat, soft, or semimetallic gasket between mating flanges in contact with the raised face portion of the flange.
Ring-Type Joint (RTJ).
This type is typically used in the most severe duties, for example, in high-pressure-gas pipe work. Ring-type metal gaskets must be used on this type of flange facing.
RTJ for API 6A Type 6B, BS 1560 and ASME B16.5 Flanges
The seal is made by plastic deformation of the RTJ gasket into the groove in the flange, resulting in intimate metal-to-metal contact between the gasket and the flange groove. The faces of the two opposing flange faces do not come into contact because a gap is maintained by the presence of the gasket. Such RTJ flanges will normally have raised faces, but flat faces may also be used
This type is typically used in the most severe duties, for example, in high-pressure-gas pipe work. Ring-type metal gaskets must be used on this type of flange facing.
RTJ for API 6A Type 6B, BS 1560 and ASME B16.5 Flanges
The seal is made by plastic deformation of the RTJ gasket into the groove in the flange, resulting in intimate metal-to-metal contact between the gasket and the flange groove. The faces of the two opposing flange faces do not come into contact because a gap is maintained by the presence of the gasket. Such RTJ flanges will normally have raised faces, but flat faces may also be used
or specified.
RTJ for API 6A Type 6BX Flanges
RTJ for API 6A Type 6BX Flanges
API 6A Type 6BX flanges have raised faces. These flanges incorporate special metal ring joint gaskets. The pitch diameter of the ring is slightly greater than the pitch diameter of the flange groove. This factor preloads the gasket and creates a pressure-energized seal. A Type 6BX flange joint that does not achieve face-to-face contact will not seal and, therefore, must not be put into
Flat Face (FF).
Flat-face flanges are a variant of raised face flanges. Sealing is achieved by compression of a flat nonmetallic gasket (very rarely a flat metallic gasket) between the grooved surfaces of the mating FF flanges. The gasket fits over the entire face of the flange. FF flanges are normally used on the least arduous of duties, such as low pressure water piping having Class 125 and Class 250 flanges
Flat-face flanges are a variant of raised face flanges. Sealing is achieved by compression of a flat nonmetallic gasket (very rarely a flat metallic gasket) between the grooved surfaces of the mating FF flanges. The gasket fits over the entire face of the flange. FF flanges are normally used on the least arduous of duties, such as low pressure water piping having Class 125 and Class 250 flanges
and flanged valves and fittings. In this case the large gasket contact area spreads the flange loading and reduces flange stresses.
Note: Both ASME B16.5 and BS 1560 specify flat face flanges and raised face
flanges as well as RTJ flanges. API 6A is specific to RTJ flanges only.
Male and Female Facings.
The female face is ³⁄₁₆-in deep, the male face is ¹⁄₄-in 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.
Tongue-and-Groove Facings.
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
The female face is ³⁄₁₆-in deep, the male face is ¹⁄₄-in 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.
Tongue-and-Groove Facings.
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.
Flange Specification and Identification
The markings include:
1. Manufacturer's trade name.
2. Nominal pipe size--the outside diameter of pipe the flange will match when welded to the pipe.
3. Primary pressure rating (also known as the flange rating)--150-Ib, 300-1b, etc.
4. Face designation--the machined gasket surface area of the flange . The flange face is the most important part of the flange. The lhs-in, raised face is common in 150-1b and 300-1b classes. Heavier ratings are ~/4-in. raised faces. A ring type joint is available in all classes, but more common in the 600-1b and greater classes.
5. Bore (also known as the nominal wall thickness of matching pipe)--the measure of the flange wall
thickness, which matches the inside dimension of the pipe being used.
6. Material designation--ASTM specifications that describe the raw materials from which the flange is made, such as ingots, blooms, billets, slabs, or bars.
7. Ring gasket number--used when the flange face is a ring type joint style.
8. Heat number or code--the batch number used by steel forgers to identify a particular batch number
of steel forgings and test results. The mill test results are made available to the purchasers of the
flanges.
Flange Dimensions
Table includes the wall thickness schedules and dimensions of ANSI flanges. The table is very useful to engineers, draftsmen, fabricators, purchasing, and material-
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