What Are the Standard Sizes of Pipe Flanges?

Pipe flanges use bolted connections and gaskets to connect pipes and piping system components (e.g. valves, fittings, pipes) to each other and to connect specialty items. They can be installed in a variety of ways including: welded, lapped, or bolted.

How Do Pipe Flanges Work?

Flanges are used to bolt together piping components such as pipes, valves, fittings, pressure components, etc. The connection uses bolts to hold the two parts together, with a gasket between them to ensure a leak-free connection. The pipe is connected to the flange using a threaded connection, weld , or via a stub end.

The components of a pipe flange connection: pipe (A), flange (B), gasket (C), bolting (D), and weld (E).

Common Flange Types and Characteristics

Flanges are not a one-type-fits-all solution. In addition to size, matching the ideal flange design to your piping system and intended use will help ensure reliable operation, long life, and optimal price.The following are the most common types of flanges.

Threaded Flanges

Also called a screwed flange, this type has a thread inside the flange bore that fits with matching male thread on the pipe or fitting. Threaded connection allows you to avoid welding in many use cases. Simply match the threading to the pipe you want to connect to.

Socket-Weld Flanges

Socket-weld flanges are ideal for smaller pipe diameters in low-temperature and low-pressure scenarios. The connection method involves placing the pipe into the flange and then using a  single multi-pass fillet weld to secure the connection. This makes this style easier to install than other types of welded flanges while avoiding the limitations associated with threaded ends.

Slip-on Flanges

Slip-on flanges are very common and are available in a variety of sizes to accommodate systems with higher flow rates and throughput. Simply match the flange to the outside diameter of the pipe to be connected. Installation is a bit more technical as you’ll need fillet weld both sides to secure the flange to the pipe..

Lap Joint Flanges

A lap joint flange is a two-piece design that requires butt welding of the stub end to the pipe or fitting with the use of a backing flange to create the flanged connection. This design makes this style popular in systems with limited physical space or systems that require frequent disassembly and maintenance.

Weld Neck Flanges

Like lap joint flanges, weld neck flanges require butt welding for installation. However, their integrity, performance in systems with many repetitive bends, and the ability to be used in high-pressure, high-temperature systems make them the first choice for process piping.

Blind Flanges

Blind flanges are used to terminate or insulate piping systems and are essentially blank discs that can be bolted together. If installed correctly and paired with the correct gaskets, they provide an excellent seal and are easy to remove when needed.

Specialty Flanges

The flange types listed above are the most common. However, there are a variety of other specialized flange types available to suit a variety of uses and environments. Other options include nipoflanges, weldoflanges, expanding flanges, orifice, long weld neck and reducing flanges.

The Many Pipe Flange Standards

There are quite a few standards that specify pipe flange sizes. The most common are ANSI, ASME, DIN, BS, and JIS. For example, ANSI flanges are based on American National Standards Institute dimensions, while JIS flanges follow Japanese industrial standards. The standard used depends on where the pipe is manufactured and installed. Choosing the right pipe flange for your application means choosing the right standard, pressure rating, diameter, bolt pattern, and face type. With so many options, it can be confusing! But most systems only require a few common sizes.

The Typical Sizes Used in Systems

For many industrial water, steam, and gas systems, you’ll typically see sizes of 1/2″, 3/4″, 1″, 1-1/2″, 2″, 3″, 4″, 6″ , 8”, 10”, 12”, 14”, 16”, 18”, 20”, 24 .Of course, larger pipes require larger pipe flanges, but the ones listed are just a few of the most common versions. You may notice that these sizes sound familiar, because they correspond to standard pipe sizes. The flange is designed to fit 40 and 80 pipe outside diameters. The flange size matches the pipe size for easy installation.