ASME B16.5 Class 150 Weld Neck Flange Dimensions Chart (Size & Bolt Hole Table)

The ASME B16.5 Class 150 Weld Neck Flange is one of the most widely used forged steel flanges in piping systems. It features a long tapered hub that provides excellent stress distribution and is designed for butt welding to the pipe, making it suitable for high-pressure and high-temperature applications.

This guide includes the complete Class 150 Weld Neck Flange dimensions, dimensional drawings, bolt hole patterns, pressure ratings, material specifications, and application recommendations to help engineers and buyers select the correct flange.

What Is a Class 150 Weld Neck Flange?

A Class 150 Weld Neck Flange (WN Flange) is a butt-weld flange manufactured according to ASME B16.5. The "150" refers to the pressure class rather than the actual working pressure.
Compared with Slip-On Flanges, Weld Neck Flanges provide:
Better fatigue resistance
Higher structural strength
Improved leak prevention
Smooth internal flow
Excellent performance under cyclic loading
These flanges are commonly used in:
Oil & Gas
Petrochemical Plants
Chemical Processing
Water Treatment
Power Stations
Offshore Pipelines
LNG Projects

What Is a Weld Neck Flange?

A Weld Neck Flange (WN Flange) is a forged flange featuring a long tapered hub that is butt-welded directly to the pipe. Unlike Slip-On Flanges, the gradual transition between the flange and pipe helps distribute stress evenly, significantly reducing stress concentration at the weld joint.This design provides excellent mechanical strength and makes Weld Neck Flanges the preferred choice for applications involving high pressure, high temperature, cyclic loading, or severe operating environments.

Understanding ASME B16.5 Weld Neck Flange Dimensions

Selecting the correct flange involves much more than matching the nominal pipe size. Every dimension specified in ASME B16.5 plays an important role in ensuring proper installation, sealing performance, and compatibility with mating flanges.
The standard defines several critical dimensions, including:

Symbol	Description
O	Outside Diameter (OD)
T	Flange Thickness
R	Raised Face Diameter
Y	Length Through Hub
X	Hub Diameter
B	Bore Diameter
C	Bolt Circle Diameter (BCD)
A	Point of Weld
Bolt Holes	Number of Bolt Holes
Hole Diameter	Diameter of Bolt Holes

Each of these dimensions is standardized to ensure that flanges from different manufacturers remain fully interchangeable when produced in accordance with ASME B16.5.
Tip: In the next section, we'll provide the complete ASME B16.5 Class 150 Weld Neck Flange Dimensions Chart, covering sizes from NPS 1/2" to 24", including outside diameter, flange thickness, raised face dimensions, hub dimensions, bolt circle, bolt hole size, and approximate weight for easy selection and comparison.

ASME B16.5 Class 150 Weld Neck Flange Dimensions Chart

The following table lists the standard dimensions for ASME B16.5 Class 150 Weld Neck Flanges. These dimensions are commonly used in industrial piping systems and ensure compatibility between flanges manufactured by different suppliers in accordance with the ASME B16.5 standard.

NPS	OD (O)	Thickness (T)	RF Dia (R)	Hub Length (Y)	Bore (B)	Bolt Circle (C)	Bolt Holes	Hole Dia
1/2	3.5	0.44	1.38	1.88	0.62	2.38	4	0.63
3/4	3.88	0.5	1.69	2.06	0.82	2.75	4	0.63
1	4.25	0.56	2	2.19	1.05	3.13	4	0.63
1-1/4	4.63	0.63	2.5	2.25	1.38	3.5	4	0.63
1-1/2	5	0.69	2.88	2.44	1.61	3.88	4	0.63
2	6	0.75	3.63	2.5	2.07	4.75	4	0.75
2-1/2	7	0.88	4.13	2.75	2.47	5.5	4	0.75
3	7.5	0.94	5	2.75	3.07	6	4	0.75
4	9	0.94	6.19	3	4.03	7.5	8	0.75
6	11	1	8.5	3.5	6.07	9.5	8	0.88
8	13.5	1.13	10.63	4	7.98	11.75	8	0.88
10	16	1.19	12.75	4	10.02	14.25	12	1
12	19	1.25	15	4.5	12	17	12	1
14	21	1.38	16.25	5	13.25	18.75	12	1.13
16	23.5	1.44	18.5	5	15.25	21.25	16	1.13
18	25	1.56	21	5.5	17.25	22.75	16	1.25
20	27.5	1.69	23	5.69	19.25	25	20	1.25
22	29.5	1.81	25.25	5.88	21.25	27.25	20	1.38
24	32	1.88	27.25	6	23.25	29.5	20	1.38

Note: The table above highlights the most commonly used Class 150 sizes. Larger sizes up to NPS 24 are also available according to ASME B16.5.

ASME B16.5 Pressure Classes

One common misunderstanding is that Class 150 means the flange can withstand 150 psi. In reality, ASME pressure classes do not directly represent the maximum working pressure. Instead, they define a pressure-temperature rating based on the flange material and operating temperature.The higher the pressure class, the thicker and stronger the flange becomes, enabling it to withstand higher operating pressures.

Pressure Class	Typical Service
Class 150	Low to medium pressure piping
Class 300	Medium pressure applications
Class 600	High-pressure process systems
Class 900	High-pressure refinery and petrochemical services
Class 1500	Severe operating conditions
Class 2500	Ultra-high-pressure industrial systems

When selecting a flange, engineers should always consider not only the pressure class but also the design temperature, piping material, process medium, and applicable engineering codes.

Common Materials for ASME B16.5 Weld Neck Flanges

Material selection directly affects the flange's mechanical properties, corrosion resistance, and service life. Choosing the appropriate material depends on the operating pressure, temperature, and conveyed medium.

Material	Typical Applications
ASTM A105	General carbon steel piping
ASTM A350 LF2	Low-temperature service
ASTM A182 F304	Food processing, water treatment
ASTM A182 F304L	Corrosive environments requiring improved weldability
ASTM A182 F316	Chemical and marine applications
ASTM A182 F316L	Highly corrosive media
ASTM A182 F11 / F22	High-temperature power plants
Duplex Stainless Steel	Offshore and seawater systems

At BAOWI STEEL, weld neck flanges are available in carbon steel, stainless steel, alloy steel, and duplex stainless steel, with full material traceability and inspection documentation available upon request.

Typical Applications

ASME B16.5 Weld Neck Flanges are widely used in industries where piping systems operate under demanding conditions. Their high mechanical strength and reliable sealing performance make them the preferred choice for critical services.
Common applications include:
Oil and gas transmission pipelines
Petrochemical processing plants
Chemical manufacturing facilities
Power generation systems
LNG terminals
Offshore platforms
Water treatment plants
Shipbuilding and marine engineering
Pharmaceutical and food processing industries

For systems involving high pressure, high temperature, or frequent thermal cycling, weld neck flanges generally provide better long-term performance than slip-on flanges.

How to Select the Right Weld Neck Flange？

Choosing the correct flange involves more than simply matching the pipe size. Engineers and buyers should evaluate several key factors before placing an order.

Pipe Size
Select a flange with the same nominal pipe size (NPS) as the connected pipe to ensure proper fit.

Pressure Class
Choose the appropriate pressure rating based on the design pressure and operating temperature. Common options include Class 150, 300, 600, 900, 1500, and 2500.

Material
Select materials that provide adequate strength and corrosion resistance for the intended service environment.

Facing Type
The sealing face should match the gasket design and mating flange. Raised Face (RF) is the most common option, while Flat Face (FF) and Ring Type Joint (RTJ) are used for specific applications.

Standards and Inspection

Ensure the flange complies with ASME B16.5 and that inspection certificates such as EN 10204 3.1, PMI, ultrasonic testing (UT), or third-party inspection are available if required.

Conclusion

ASME B16.5 Weld Neck Flanges are the preferred choice for industrial piping systems requiring high strength, reliable sealing, and long-term performance. By following standardized dimensions and pressure classes, they ensure compatibility, safety, and efficient installation across a wide range of industries.
Selecting the correct flange involves evaluating pipe size, pressure rating, material, and service conditions. Working with an experienced manufacturer also helps ensure consistent quality, full traceability, and compliance with international standards.

Frequently Asked Questions (FAQ)

1. What is the difference between ASME B16.5 and ANSI B16.5?
ANSI B16.5 is the former designation of the standard. Today, it is officially published and maintained by ASME, so the correct designation is ASME B16.5.

2. What sizes are covered by ASME B16.5?
The standard covers nominal pipe sizes from NPS 1/2" to NPS 24". Larger diameters are generally covered by ASME B16.47.

3. What is the difference between a Weld Neck Flange and a Slip-On Flange?
A Weld Neck Flange is butt-welded to the pipe and provides higher strength and better fatigue resistance, making it suitable for high-pressure and high-temperature applications. A Slip-On Flange slides over the pipe and is generally used for lower-pressure systems.

4. Does Class 150 mean the flange can withstand 150 psi?
No. The pressure class is a rating defined by ASME B16.5 and varies with material and operating temperature. It does not directly represent the maximum working pressure in psi.

5.Can BAOWI STEEL provide customized flanges?

Yes. We offer customized dimensions, special materials, machining services, and OEM marking according to customer drawings and project specifications.

6.What Is the Difference Between ASTM A105 and ASME SA105?
There is virtually no difference in material properties between ASTM A105 and ASME SA105. ASTM A105 is the ASTM material specification, while ASME SA105 is the equivalent specification adopted by the ASME Boiler and Pressure Vessel Code for pressure piping applications.