Which are the most common types of flanges used in piping? How do they look like? The key types of flanges are the welding neck, long welding neck, slip-on flanges, socket weld, lap joint, threaded and blind flanges. In addition to these standard flanges, some special ones exist, called Weldoflange/Nipoflange and Elboflange, swivel flange, expander/reducer flange, and orifice flanges. 

STANDARD TYPES OF FLANGES

The type of flange to be used for a piping application depends, mainly, on the required strength for the flanged joint. Flanges are used, alternatively to welded connections, to facilitate maintenance operations (a flanged joint can be dismantled quickly and conveniently).

Let’s now dive in, showing the key types of flanges with pictures.

WELDING NECK FLANGE

STANDARD TYPES OF FLANGES

The type of flange to be used for a piping application depends, mainly, on the required strength for the flanged joint. Flanges are used, alternatively to welded connections, to facilitate maintenance operations (a flanged joint can be dismantled quickly and conveniently).

Let’s now dive in, showing the key types of flanges with pictures.

WELDING NECK FLANGE

Long weld neck flanges (“LWN”) are similar to welding neck flanges, with the exception that the neck (tapered hub) is extended and acts like a boring extension.

Long weld neck flanges are generally used on vessels, columns or barrels. These flange types are available also in the heavy barrel (HB) and equal barrel (E) types.

SLIP ON FLANGE

A slip-on flange is connected to the pipe or the fittings by two fillet welds, one executed inside and one outside the cavity of the flange.

The bore size of a slip-on flange is larger than the outside diameter of the connecting pipe, as the pipe has to slide inside the flange to be connected by the execution of a fillet weld.

Slip-on flanges are also defined “Hubbed Flanges” and they are easy to recognize due to their slim and compact shape.

The dimensions and weights of slip-on flanges ANSI/ASME are available on this page.

WELD NECK VS SLIP ON FLANGE

Flanged joints made with slip-on flanges are, in the long run, a bit more fragile than connections made with welding neck flanges (in similar service conditions). This seems due to the following facts:

a welding neck flange features a tapered hub, absent in a socket weld flange, which distributes the mechanical stress between the pipe and the flange more evenly

a welding neck joint as only one welding area instead of two (socket weld flange).

Another advantage of the welding neck flange is that it can be connected either to pipes and fittings, whereas socket weld flanges suit pipes only.