Steel pipe flanges are most commonly used to join lengths of pipe. Normally found at one end of a pipe, or occasionally both ends, a steel pipe flange is a lip or ring that sticks out from the pipe or tube, perpendicular to the length. By design, this lip provides a mating surface that can be bolted to another flange or connect a handrail pipe to a wall. The handrail pipe-to-wall connection also uses a type of steel pipe flange. Although there are alternate methods for these types of connections, such as welding or threading, a steel pipe flange can make this type of assembly much easier.
There are many types of steel pipe flanges, the majority of which provide corresponding bolt patterns for a simple bolted assembly. The overall reason pipes are generally connected by some type of steel pipe flange system is efficiency. For example, in most industrial applications, the individual parts of a plumbing system are pre-determined. Should one section become damaged and require replacement, the repair can be as easy as removing bolts from the flanges at both ends of the pipe, replacing the section, and re-bolting them. This method can be much faster and cleaner than some of the alternatives, such as welding or soldering.
One notable advantage for using a bolted flange is the lack of special tooling required. In contrast, joining pipes without the advantage of a flange system can involve welding or specialized threading machines. Welding pipes that lack flanges can be hazardous in certain environments, such as paper or lumber mills where the risk of fire is high.
Like the rim around a top hat, a steel flange around the end of a pipe provides a place where bolts can fasten one end of a pipe to another. If, by chance, the steel pipe is not part of a plumbing system, a flange may still be employed. For example, the base of a flagpole may contain a steel pipe flange for fastening it to a deck or platform.
Not all steel pipe flanges are designed for bolting, however. Certain types are designed specifically for welding. A welded steel pipe flange virtually removes any risk of leaks, but introduces new challenges when it comes to repairing a damaged flange or section of pipe. Simply unbolting a connection, rather than cutting steel pipes, is intentionally a much easier and cleaner process.