Weld Neck Flange vs Slip On Flange: Key Differences, Advantages and Uses

When you are tasked with selecting between either a weld neck or a slip on flange then it is important to remember that the type of flange considered affects the connection being made and the overall cost. Not only is it true that choosing between a weld neck and a slip on flange impacts which flanges are used but also the pressure and temperature versions used during connection. 

Kalpataru Piping Solutions supply custom flange products as well as standard flanges and operate within the industrial sector. All specifications are catered for including joint design, size of flange selected, and type of flange. This guide compares the two flange types by design, connection method, strength, fatigue considerations, dimensions, cost, standards, and applications. It also provides a practical flange selection guide to help engineers and procurement teams understand where each flange type is commonly specified.

What Is a Weld Neck Flange?

A weld neck flange has a long tapered hub that connects to the pipe through a butt weld. The bore of the flange is machined to match the pipe inside diameter and wall thickness so that the pipe and flange form a continuous internal passage.

The tapered hub is an important part of the design. Instead of placing the main transition directly at the flange face, the gradual change in section helps distribute stresses over a larger area. This makes the design suitable for piping exposed to pressure, temperature changes, vibration, and repeated loading.

The butt weld also provides a direct welded connection between the pipe and flange. Because the joint can be examined using applicable nondestructive examination methods, weld neck flange designs are commonly selected for critical piping where weld quality and stress control are important.

What Is a Slip-On Flange?

A slip on flange has a flat body with a bore that allows the pipe to pass through the flange. The pipe is positioned inside the flange, and the connection is normally completed using fillet welds.

The design makes alignment and installation relatively straightforward and is one reason slip-on flanges are widely used in lower pressure and general utility piping.

For a detailed explanation of slip on flange types, specifications, dimensions, weights, welding, and installation, see Kalpataru’s Complete Guide on Slip On Flanges rather than repeating that information here.

Weld Neck vs Slip On Flange Comparison

The most important differences between the two designs are related to the way the pipe connects to the flange and how loads are transferred through that connection.

There is no universal rule that one flange type should replace the other. The correct selection depends on the design conditions and the applicable piping specification.

Dimensional Comparison between Weld Neck and Slip on flange

Dimensions vary with nominal pipe size and pressure class, so flange dimensions should always be confirmed against the applicable standard and purchase specification.

For comparison, the following Class 150 figures show how the geometry differs for common sizes. The values are based on published ASME B16.5 dimensional tables.

The dimensional data shows an important difference in geometry. At these Class 150 sizes, the flange thickness is the same or very similar between the two designs, while the weld neck flange has a substantially longer hub section.

For example, the published Class 150 data gives a 63.6 mm H dimension for an NPS 2 weld neck flange compared with 25.6 mm for the slip-on design. At NPS 6, the corresponding dimensions are 88.6 mm and 39.6 mm.

What Does Each Flange Type Cost to Install?

Initial purchase price is often one of the first factors considered during flange selection, but the flange price alone does not represent the complete installed cost.

The final cost difference therefore depends on size, pressure class, material, quantity, welding procedure, inspection requirements and project location. A lower flange purchase price does not automatically mean a lower total project cost.

Flange Selection Guide

The following table provides a practical starting point when comparing a weld neck vs slip on flange.

This is a selection guide rather than a substitute for engineering design. Pressure, temperature, pipe material, fluid service, corrosion allowance, fatigue, welding requirements and the governing code should all be considered before final selection.

Materials and Standards for Flange Selection

Material selection is an important part of any flange selection guide and should consider fluid, pressure, temperature, corrosion conditions, and the applicable code. Kalpataru supplies weld neck flanges in carbon steel, alloy steel, stainless steel, duplex, super duplex, copper, and nickel alloys, including Nickel 200,Monel 400, Inconel 600, Inconel 625 and Hastelloy C276. Its slip on flangesinclude carbon steel, alloy steel, stainless steel, duplex, super duplex, nickel alloys, copper alloys and titanium. Common grades include ASTM A105 and ASTM A182 F5, F9, F11, F22 and F91. For carbon steel requirements, see the ASTM A105 Flange Manufacturerpage. ASME B16.5 flanges cover NPS 1/2 to NPS 24 and define ratings, materials, dimensions, tolerances, marking and testing.

Frequently Asked Questions