Weld Neck and Slip On Flanges Differences and Material Selection

In piping systems, ASME B16.5 flanges are commonly used connection components, widely applied for quick connection and disassembly between pipes, equipment, and instruments. Weld neck and slip on flanges are the two most common types of flanges, each offering unique advantages in design, installation, and application. Understanding the differences between these two flange types is critical for decision-making during selection and construction processes.

What Are Weld Neck Flanges?

Weld Neck Flanges feature a conical neck design and are connected to pipes via butt welding, making them particularly suitable for high-pressure and high-temperature applications. The extended neck structure effectively distributes stress, significantly enhancing the pressure resistance and deformation resistance of the connection.

The unique feature of this flange lies in its combination of a conical hub and extended neck design. The neck transitions smoothly to the pipeline via a gradual gradient, creating a seamless connection interface. This structure not only ensures the integrity of the welded joint but also effectively reduces the risk of turbulence and erosion caused by medium flow at the connection point.

What Are Slip On Flanges?

The structural feature of slip on flanges is that their inner diameter is slightly larger than the outer diameter of the pipe. During installation, they can be directly slipped onto the end of the pipe and secured by welding along the outer edge. This type of flange has a relatively simple structure and is easy to install.

In design, slip-on flanges omit the hub and neck structures of weld neck flanges, requiring only two fillet welds for fixation. While this simplified design enhances installation efficiency, it lacks fully penetrated welds, resulting in relatively weaker structural strength and pressure resistance. Compared to weld neck flanges, slip on flanges are more suitable for medium-to-low pressure applications and offer significant advantages in scenarios requiring rapid installation and where strength requirements are not stringent.

Weld Neck Flanges VS Slip On Flanges

Weld neck flanges and slip on flanges are two common types of flanges. Their main differences lie in design, installation techniques, and applications. In this article, we will outline the key differences between weld neck flanges and slip on flanges to help you choose the most suitable type for your piping system.

Characteristics	Slip On Flange（SO）	Weld Neck Flange（WN）
Structural features	The flange is welded after sliding into the pipe end, featuring a simple structure	The flange neck is welded to the pipe end, and the flange design is relatively complex.
Applicable pressure range	Suitable for low-pressure and low-temperature environments	Suitable for harsh environments such as high pressure, high temperature, and vibration.
Stress resistance	Weaker, prone to stress concentration, suitable for applications not subjected to high pressure	Strong, capable of evenly distributing stress, suitable for high-pressure applications.
Welding requirements	Simple welding process with lower welding requirements	High welding requirements, precise alignment is necessary, and welding quality is strictly controlled.
Installation difficulty	Easy to install, the flange is directly slid into the pipe end for quick completion	Installation is relatively complex, requiring precise alignment and high-quality welding.
Manufacturing process	Steel plate cutting and processing	Forging + precision machining
Cost	Lower manufacturing costs, lower installation costs	Higher manufacturing costs, higher installation costs, and require more time and technical support
Service life	Shorter service life, suitable for low-pressure and low-temperature conditions	Longer service life, suitable for high-temperature and high-pressure environments, with enhanced durability
Common application areas	Suitable for low-pressure pipelines and projects with limited budgets	Widely used in high-temperature and high-pressure pipeline systems in industries such as petroleum, chemicals, and power

Flanges Material Selection

Alloy Steel	ASTM A182 F5 / F9 / F11 / F12 / F22 / F91 / F92
Stainless Steel	ASTM A182 F304 / 304L / 304H、F316 / 316L、F317、F310S、F321、F347、F904L
Duplex stainless Steel	ASTM A182 F51 / 53 / 55 / 60
Carbon Steel	ASTM A105 / A105N
Low-temperature Steel	ASTM A350 LF2 / LF3
Pipeline Steel	ASTM A694 F42 / 46 / 52 / 56 / 65 / 70

How to choose?

Ideal Applications for Slip On Flanges

Slip on flanges are ideal for low- to medium-pressure applications, such as water supply systems, HVAC installations, and certain chemical processing conditions. They offer easy installation and lower initial costs, making them an attractive solution when high durability is not a primary concern.

Ideal Applications for Weld Neck Flanges

weld neck flanges are an excellent solution for high-pressure systems and locations where durability is of utmost importance, such as petrochemical plants, high-temperature pipelines, and other critical infrastructure that relies on stable operation under pressure. Their design makes them suitable for use with hazardous fluids like gasoline or even high-pressure fluids without deteriorating over time, a valuable characteristic that sets butt-weld flanges apart.

Conclusion

Weld neck flanges and slip on flanges specified in the ASME B16.5 standard each have their own characteristics in piping systems, and their selection should be based on specific operating conditions. Weld neck flanges, with their excellent mechanical strength, durability, and sealing performance, are particularly suitable for high-pressure operating conditions. In contrast, slip on flanges, with their ease of installation and cost-effectiveness, are more suitable for medium- and low-pressure piping systems. These two types of flanges complement each other well in industrial applications.