Steel Flange Dimensions Chart

What is a steel flange?

A steel flange is a steel annular disc-shaped component used to connect pipes, valves, and equipment. It is bolted and sealed to achieve a detachable connection of the pipeline system. It is a key component in industrial pipeline systems and is widely used in petroleum, chemical, electric power, shipbuilding and other fields.

Steel Flange Dimensions & Sizes:

The dimension & size of a steel flange depends on its flange type, pressure rating and applicable standards. The following are the typical size ranges of steel flanges under international general standards (ASME, EN, GB, etc.):

1. American Standard Flange (ASME B16.5 & B16.47)

Flange Type	Size Range (NPS)	Pressure Rating (Class)	Applicable Standards
Welding Flange (WN)	1/2" ~ 24"	150 ~ 2500	ASME B16.5
Socket Weld (SW)	1/2" ~ 4"	300 ~ 6000	ASME B16.5
Threaded Flange (THD)	1/2" ~ 12"	150 ~ 2500	ASME B16.5
Blind Flange (BL)	1/2" ~ 60"	150 ~ 2500	ASME B16.5/ASME B16.47
Large Diameter Flange	26" ~ 60"	75 ~ 900	ASME B16.47

Note:

NPS (Nominal Pipe Size): Nominal diameter expressed in inches (e.g. NPS 2" ≈ DN50).
Class: American standard pressure class (Class 150 ≈ PN20, Class 300 ≈ PN50).

2. European standard flange (EN 1092-1)

Flange type	Size range (DN)	Pressure class (PN)	Applicable standard
PL (slip-on flange)	DN10 ~ DN4000	PN6 ~ PN100	EN 1092-1
WN (butt-weld flange)	DN10 ~ DN2000	PN10 ~ PN400	EN 1092-1
SO (loose flange)	DN15 ~ DN600	PN6 ~ PN40	EN 1092-1
BL (blind flange)	DN15 ~ DN3000	PN6 ~ PN400	EN 1092-1

Note:

DN (nominal diameter): expressed in millimeters (e.g. DN100 ≈ NPS 4").
PN (nominal pressure): European standard pressure level (PN16 ≈ 16 bar).

3. Chinese standard flange (GB/T 9119 & HG/T 20592)

Flange type	Size range (DN)	Pressure level (PN)	Applicable standards
Slip-on flange (PL)	DN10 ~ DN2000	PN0.25 ~ PN10	GB/T 9119
Butt welding flange (WN)	DN10 ~ DN2000	PN10 ~ PN160	GB/T 9115
Socket welding (SW)	DN10 ~ DN80	PN10 ~ PN160	HG/T 20592
Threaded flange (TH)	DN8 ~ DN150	PN10 ~ PN63	GB/T 9114

Note:
Chinese standard flange is compatible with both American standard (Class) and European standard (PN) systems, for example, HG/T 20592 includes Class 150 ~ 2500 flanges.

4. Special flange size range

API 6A flange
Size range: 2-1/16" ~ 21-1/4"
Applicable standard: API 6A (wellhead equipment)

JIS flange
Size range: DN10 ~ DN1000
Applicable standard: JIS B2220

DIN flange
Size range: DN10 ~ DN4000
Applicable standard: DIN 2576/2633

American standard flanges (ASME B16.5 & B16.47):

The following mainly introduces the size specification table of American standard flanges (ASME B16.5 & B16.47), covering common flange types, pressure levels and key size parameters.

American standard flange standard classification:

ASME B16.5: pipe flanges and flange fittings
Pressure level (Class): 150, 300, 600, 900, 1500, 2500
Size range (NPS): ½" ~ 24"

ASME B16.47: large diameter flange (Series A/B)
Pressure level (Class): 75, 150, 300, 400, 600, 900
Size range (NPS): 26" ~ 60"

API 6A: high pressure flange for wellhead equipment
Pressure level (Class): 2000, 3000, 5000, 10000 psi

Size range (NPS): 2-1/16" ~ 21-1/4"

Steel Flange Dimensions & Sizes Chart:

ASME B16.47 Reducing Flange Dimension Chart:

ASME B16.47 B16.47 Series A（MSS SP-44）Reducing Flange Dimensions Chart:

ASME B16.47 Series B Reducing Flange Dimensions Chart:

How to choose flange size?

Material matching:
ASTM A105 (carbon steel) is suitable for conventional working conditions.
ASTM A182 F304/F316 (stainless steel) for corrosive media.

Matching pipe size: The DN/NPS of the flange must be consistent with the pipe.
Pressure level: Select PN/Class according to the system working pressure (e.g. PN16 ≈ Class 150).
Bolt specification: Class 300 flanges require ASTM A193 B7 bolts (high-strength alloy steel).
High temperature/high pressure correction: Class 150 flanges need to be derated above 200°C.

Flange type:
High pressure/high temperature → Butt welding flange (WN)
Low pressure/small diameter → Flat welding flange (PL)
Frequent disassembly → Loose flange (SO)

Frequently Asked Questions:

Q: What do "DN" and "PN" or "Class" on a flange represent?

A:
1. DN: Represents the nominal size. DN is not the actual measured size but a "nominal size" used for identification. Flanges of different standards may have slightly different actual inner or outer diameters, but as long as the DN is the same, they can be matched. The PN series is commonly found in European standards (DIN) and Chinese standards (GB). For example, PN10, PN16, PN25, PN40. The number represents the maximum working pressure in "bar" (at 20°C).

2. PN / Class: Pressure rating, representing the maximum permissible working pressure that the flange can withstand at a certain temperature. The Class series is commonly found in American standards (ASME). For example, Class150, Class300, Class600. This number is a dimensionless rating and does not directly equal the pressure value. The higher the Class number, the stronger the pressure resistance, and the larger the flange size and thickness.

Note: PN and Class do not have a direct mathematical conversion relationship! They belong to different standard systems. When selecting flanges, the system specified in the design documents must be followed; mixing different types is not allowed.

Q: How to ensure two flanges can be installed together?
A: Flange mating requires meeting three matching principles:

1. Size Matching: The nominal sizes must be the same: one DN150 flange must be connected to another DN150 flange.
Pressure Rating Matching: one PN16 flange must be connected to another PN16 flange. Flanges with different pressure ratings may have different bolt hole sizes, center distances, and flange thicknesses, making forced mating impossible.

2. Standard Matching: It is best to follow the same standard system. For example, one ASME B16.5 Class 150 flange should be mated with another ASME B16.5 Class 150 flange. Although different standards (such as GB and DIN) may be compatible in some specifications, there is a risk, and mixing them is not recommended.

3. Sealing Face Type Matching: The sealing face types of the flanges must be compatible.
Matching principle: RF to RF, FF to FF, RTJ to RTJ, T to G.

Q: How to choose the flange sealing face type (RF, FF, RTJ, etc.)?

A: Simple selection principle:
General operating conditions: Choose RF.
Low-pressure, cast iron equipment: FF may be used.
High-pressure oil and gas, chemical: Choose RTJ.

Q: Are American standard (Class) and European standard (PN) flanges interchangeable?
A: In principle, they are not directly interchangeable.

Size differences: Even if the DN and theoretical pressure are similar (e.g., DN100 PN40 and DN100 Class300), their key dimensions such as bolt hole center distance, bolt hole diameter, and flange thickness may differ, making alignment impossible.
Pressure-temperature rating differences: The two systems define different maximum allowable working pressures for the same material at different temperatures.
Exception: There is a type of "transition flange" on the market, with one end being PN series and the other end being Class series, specifically designed to connect systems of different standards. It is used in projects with both American standard equipment and European standard piping.

Q: When selecting a flange, besides DN and PN, what other parameters should be considered?

A: Flange type: WN/SO/BL, etc.
Material: ASTM A105/ASTM A182
Bolt holes: The number, diameter, and center circle diameter must be exactly the same as the mating flange.
Gaskets and bolts: Select the correct gasket (e.g., non-metallic gasket, spiral wound gasket, metal ring gasket) based on the flange's sealing surface type, pressure rating, and media.
The bolt material and length must meet pressure and temperature requirements.

Q: What does the flange's pressure-temperature rating mean?
A: The flange's permissible working pressure is not a fixed value but varies with temperature.

For example, a PN16 flange can withstand 16 bar of pressure at 20°C. However, when the temperature rises to 200°C, the material's strength decreases, and its maximum permissible working pressure may drop to 12 bar.

Conclusion:
Steel flanges have a wide range of sizes, from DN10 (NPS 1/8") to DN4000 (NPS 160"), covering almost all industrial pipeline needs. When selecting, factors such as standards, pressure, temperature, and media should be considered.

Read more: How to Choose the Appropriate Pipe Flange Size? or How are Pipe Flanges Manufactured?