A common type of curved structural steel is the angle ring or angle flange. Commonly made of carbon steel, stainless steel or aluminum, an angle ring is made by rolling a piece of structural angle into a ring and then welding the ends together. Typically, the ring is rolled with the horizontal leg radiating out from the center to create what is called a “leg-out angle ring” (as opposed to a “leg-in angle ring” or “off-axis” angle ring.)
These rings are commonly manufactured to standard diameters, but they also can be made to custom specifications. They are used as flanges to connect pipe or to connect to equipment such as a fan. The flanges can be welded together or bolted. In this latter case, the angle iron flanges are provided with bolt holes once again either with standard sizes and locations or with special patterns.
The holes can be put in the angle by several means: drilled, punched by a mechanical or hydraulic press, or punched or drilled by automated equipment. For connection purposes it is important not only that the holes be located with the correct bolt circle and spacing but also that the bolt circle be concentric with the angle ring.
Large angle rings can be made by connecting ring segments. Ring segments are rolled and commonly cut to length and fitted up into full rings before the holes are put in. The holes can be drilled or punched. After the holes are put in, the ring can be shipped “as is” or cut apart again. In this last case, the ends to be connected are often match marked for reassembly. This method is sometimes required when the completed ring would be too large to ship.