Introduction

There are many different types of piping flange due to the different service conditions in which they operate. Flanges are chosen based on their corrosion resistance properties, erosion resistance properties, pressure temperature rating (Class), number of welds required for attachment, physical size (some flange designs may not fit into the space allowed) and cost. The most common flange types are:

Flange Types

Flange Types

Other flange types many engineers will encounter are the male and female, and tongue and groove types. Less common types include the orifice, expander, reducing, and long welding neck flange designs.

Flange ends may be screwed, welded, or lapped (metal to metal contact) to their associated piping.

The most popular flange types will be discussed in this section.

 

Flange Types Overview

Some important information concerning flange types has been compiled into the below table. Although ASME standards are cited in the table, alternative international and national standards are available (DIN, EN etc.). ASME is however the most widely accepted piping standards organisation, and for this reason its standards have been cited. 

In the below table, the ‘Faces’ column indicates the usual sealing face chosen per flange type. However, there may be exceptions to the rule depending upon the flange type. The table should be treated as a general overview table, whilst specific information should be sought in relevant standards. 

Flange Type

NPS (inch)

ASME Class

Faces

Joint Integrity

Weld

ASME Standards

Welding Neck Flange

All

All

All

High

One butt weld.

B16.5, B31.3

Slip-on Flange

Many

Generally, ≤ 600

FF, RF

Medium

One or two fillet welds.

B16.5, B31.3

Socket Weld Flange

Generally,
≤ ½ to 2.

Max ≤ 4

≤ 600

FF, RF

Medium

One fillet weld.

B16.5, B31.3

Lap Joint Ring Flange

Not used for small sizes.

NA

FF

NA

None

B16.5, B31.3

Stub End of Lap Joint Flange

150 to 2500

FF, RF, RTJ

High

One butt weld.

B16.9, B31.3

Threaded Flange

Generally,
≤ ½ to 2.

Max ≤ 4

≤ 300

FF, RF

Low

None

B1.20.1, B31.3

Blind Flange

All

All

All

NA

None

B16.5, B31.3

Flange Type Summary Table

Table Key:   FF– flat face.    RF–raised face.    RTJ–ring type joint.

 

Special Flange Types

Various special flange types exist, these include the reducer, expander, long welding neck, nipoflange, weldoflange, and swivel flange designs. As special flange types are not common, they are not covered in this introductory material. 

 

Flange Types, Faces, and Surfaces - Explained!

This video is part of our Piping Flange Fundamentals Video Course

 

Additional Resources

http://www.wermac.org/flanges/flanges_raised-face_flat-face_ring-type-joint.html

https://www.kamleshmetal.com/flanges-faces-types.html

https://www.theprocesspiping.com/introduction-to-flanges/