Slip On Flange vs Weld Neck Flange – What’s the Difference?

When selecting flanges for your piping system, the two most commonly used types are Slip On Flanges (SO Flanges) and Weld Neck Flanges (WN Flanges). Though they may appear similar at first glance, their differences in design, performance, and application are critical when choosing the right component for your system.

This in-depth guide will help you understand:

• The key differences between slip on and weld neck flanges

• Pros and cons of each flange type

• Application scenarios

• Factors to consider before selecting

Whether you're designing high-pressure pipelines, process systems, or general plumbing infrastructure, this article will give you the knowledge to make an informed decision.

What Is a Slip On Flange?

A Slip On Flange is a type of flange that is slid over the pipe and then welded both inside and outside to secure it in place. It has a low hub and is typically easier to align and install than a weld neck flange.

Key Features:

Slides over the pipe

Requires two welds (one inside, one outside)

Less protrusion from the pipe
Suitable for low to medium pressure applications

What Is a Weld Neck Flange?

A Weld Neck Flange, also known as a high-hub flange, features a long tapered hub that gradually transfers stress from the flange to the pipe. It is butt-welded to the pipe, forming a very strong, leak-proof connection.

Key Features:

• Tapered neck for high-stress distribution

• Requires butt welding

• Ideal for high-pressure and high-temperature environments

• Typically used in critical process piping

Slip On Flange vs Weld Neck Flange – Quick Comparison

Benefits of Slip On Flanges

1. Ease of Installation

Slip on flanges are easier to position and align with the pipe. This makes them ideal for field installation where precision is difficult to achieve.

2. Lower Cost

The production cost is generally lower, and the welding process requires less skill than a butt-weld.

3. Versatile Applications

Commonly used in cooling water lines, fire protection systems, and low-pressure process systems.

Drawbacks of Slip On Flanges

• Lower pressure resistance than weld neck flanges

• Weaker structural integrity due to fillet welds

• Not ideal for cyclic loading or high-stress environments

• Requires precise welding on both inner and outer surfaces to prevent leaks

Benefits of Weld Neck Flanges

1. Superior Strength

The tapered hub distributes mechanical stress evenly, reducing the chance of failure under pressure.

2. Leak-Proof Connection

The butt-weld connection forms a smooth transition between pipe and flange, minimizing turbulence and erosion.

3. Ideal for Harsh Conditions

Weld neck flanges are the top choice for:

• High-pressure pipelines

• High-temperature systems

• Flammable or hazardous fluid transport

• Subsea or offshore installations

Drawbacks of Weld Neck Flanges

• Higher cost of both the flange and installation

• Requires skilled welding personnel

• Not ideal for projects with tight budgets or limited technical expertise

Applications – When to Use Each Type

✔ Use Slip On Flanges When:

• The system operates under low to moderate pressure

• Budget is limited

• The system does not experience frequent temperature/pressure changes

• Ease of alignment and installation is a top priority

• Used in HVAC, water pipelines, compressed air systems, and fire sprinklers

✔ Use Weld Neck Flanges When:

• The system operates at high pressure or high temperature

• Fluid integrity and leak prevention are critical

• You’re dealing with hazardous fluids or volatile environments

• Fatigue resistance is required

• Common in refineries, petrochemical plants, nuclear power, and marine applications

Material Considerations for Both Flange Types

Both slip on and weld neck flanges are available in a variety of materials, including:

• Carbon Steel – Economical, strong, good for general use

• Stainless Steel – Corrosion-resistant, used in food, pharma, and marine

• Alloy Steel – High strength, great for high-temperature applications

• Duplex/Super Duplex – Used in offshore and aggressive chemical environments

Choose material based on:

• Operating temperature

• Chemical compatibility

• Corrosion exposure

• Regulatory standards (ASME, API, ISO)

Flange Standards to Know

Both flange types adhere to international standards, ensuring compatibility and safety. Common standards include:

• ASME B16.5 – For pipe sizes up to 24"

• ASME B16.47 – For pipe sizes above 24"

• API 6A – Used in oil & gas applications

• EN 1092-1 – European standard for steel flanges

Always ensure your flange type, size, material, and pressure class meet your project’s code and regulatory requirements.

Common Mistakes to Avoid

• Interchanging the two flanges without considering application needs

• Using slip on flanges in high-pressure systems where weld necks are required

• Skipping proper welding inspection especially for weld neck connections

• Ignoring material compatibility with process fluids

• Improper alignment during installation, leading to long-term stress and failure

Final Verdict: Which One Should You Choose?

There’s no one-size-fits-all answer, but here’s a general guideline:

• Choose a Slip On Flange if you're working with low-pressure systems and need a budget-friendly, easy-to-install solution.

• Choose a Weld Neck Flange if your system demands strength, leak resistance, and long-term reliability under tough conditions.

For critical process systems, never compromise—the weld neck flange is the gold standard in performance and safety.

Conclusion

Understanding the difference between slip on and weld neck flanges is essential for building safe and efficient piping systems. Each flange serves a unique purpose and performs best under specific conditions. The right flange will offer long-term reliability, cost efficiency, and system integrity.

If you're designing or upgrading a piping system, take the time to evaluate your operational needs, system pressure, temperature, and fluid compatibility before making your final flange selection.

Need help choosing the right flange for your project?

Dikai engineering team is ready to assist you. We offer a full range of ASME-certified Slip On and Weld Neck Flanges in carbon steel, stainless steel, and specialty alloys. Contact us today for expert advice or a free quote!