Flanges are used in petrochemical, oil and gas, power generation and other industrial applications to connect pipes, valves and pumps. Pipe flanges connect piping systems and allow for efficient flow of liquids or gases. The proper selection, installation and alignment of flanges is critical in preventing leaks and damage to the system. Flanges, like most components, can be damaged due to poorly fitted gaskets, excessive vibration, corrosion or improper installation. Any of these factors can lead to serious system failure, causing thermal shock, excessive loads, stress shocks or stress cracking corrosion, resulting in excessive lateral or rotational flange misalignment. When performing maintenance, a previously assembled flanged joint can spring out of alignment in any direction around its circumference.

Pipe flanges are used to mechanically connect two pipes, or a pipe to a valve, tee, choke, or any equipment used to create a piping system.  Pipe flanges are bolted, welded, or threaded together or connected to a piece of equipment, incorporating a gasket to provide a tight seal.  Flanges are only second to welding as the most used method to join piping systems. 

Code 61/Code 62 Caterpillar® Flange (SAE J518) 

In referring to the various types of flanges used in the world markets, it is important to make the comparison to the Caterpillar Code 61 and 62 flange (SAE J518).  As with other flanges, the female porthole on the Caterpillar flange is unthreaded with 4 bolt holes surrounding it at the corners. The male has a flanged head with an O-ring grove and with holes to match the port.

GAZ Poclain 24° Flange

Like Caterpillar in the U.S. and Komatsu in Japan, there is a French standard flange fitting known as the Poclain 24 flange. The Poclain flange derives its name from the Poclain excavator company, founded by Georges Bataille in France in 1927 and was a leader on the world market because of its revolutionary hydraulic motor.  

JIS 4-Bolt Flanges are frequently used in fluid power systems. There are two pressure ratings: Type I Code 61 and Type II Code 62. 

As with DIN flanges, the unthreaded female port in a JIS flange has 4 bolt holes at the corners.  The male flanged head has holes to match the port and a grooved recess for an O-ring.

The O-ring makes the seal between the flanged head and the flat surface on the port.  Threaded bolts are inserted through the 4 bolt holes to securely connect the flange to another mating flange or the flat surface of the port. 

One type of international flange is the DIN 4-Bolt Flange. DIN means, "German Institute for Standardization." These DIN flanges are similar to SAE Code 61 and SAE Code 62 flanges. 

For this particular DIN flange, the unthreaded female port has 4 bolt holes around it in the corners.  The male flanged head has holes to match the port and a grooved recess for an O-ring.

The O-ring makes the seal between the flanged head and the flat surface on the port.  Threaded bolts are inserted through the 4 bolt holes to securely connect the flange to another mating flange or the flat surface of the port. 

Flange Plugs

 Among the category of flange fittings (or flange adapters) are flange plug caps, which are used to cap off or block the flow in the pipe. Flange plugs are basically a flange without a center hole that closes the end of a pipe when bolted to a standard mating flange. Depending on the system requirements, these flange plug caps are typically gas or liquid-tight. For gray water subsurface irrigation, they are sometimes used to force waste through perforated holes in the pipe, driven by system pressure.

Flange Fittings & How They Fit In

The fluid power industry is making a shift to connections with an elastomeric O-ring seal, to minimize leakage. These fittings include the SAE straight thread, face seal, ISO 6149, SAE  J518 (Code 61 and Code 62) flange fittings and flanges (Code 61 and Code 62), where the O-ring seal is compatible with the fluid.

 Not Interchangeable

 It is important to note that the two flange fitting style codes (61 and 62) are not interchangeable due to their pressure ranges and their different bolt patterns. As shown in this diagram of overlapping code 61 and code 62 4-bolt flange fittings, the dimensional placement of holes is close, but not identical. Note the difference in the bolt-hole’s center-to-center dimensions.

Benefits of Flanges

 Though there are specific applications where flanges and/or flange fittings are the only practical choice (particularly in larger, high-pressure piping applications), flange fittings sometimes provide benefits to the piping system that traditional hydraulic fitting types do not. For instance, in those larger OD applications, flanges are often able to be connected to pipe (tube or hose) and component ports more easily than threaded fittings or adapters. Most importantly, in many severe service applications on mobile construction equipment flanged connections are best for: