Many industries, including liquid petroleum gas (LPG), chemical & petrochemical, energy, and process piping, etc. have a large requirement for pipe fittings including elbows, sweeps and returns. These industries deal with the transferring of gases and liquids within their processing facilities and between one another on a daily basis. Elbows, sweeps and returns are used to make a connection between two straight lengths of pipe or tube when the direction of the piping needs to change. Elbows are generally described as a bend between 45deg and anything less than 180deg. Sweeps are gradual bends and usually described as anything less than 45deg of bend. And returns are just that, 180deg of bend; making a return to the direction from which it came.
These pipe/tube fittings are generally described in one of two different ways; short radius or long radius bends. Long radius elbows, sweeps and or returns are generally considered anything over a 3D bend but usually not exceeding a 6D bend. Short radius elbows, sweeps and or returns are usually considered to be anything under a 3D bend. The description of these fittings, i.e. 3D, 5D, 6D are directly correlated to the pipe/tubes diameter, where the number before the “D” is the amount you multiply the diameter of the tube/pipe by. For example, a 3D bend on a 2” tube would be a 6” center line radius (CLR).
Short Radius pipe/tube fittings can be made through a number of different processes including cold and hot forming but 2 of these are most common. The 1st of these processes to be considered and the most common of methods to obtain elbows, sweeps and or returns is rotary draw bending or as most people call it mandrel bending. Rotary draw bending is a precise technology as it requires a specific set of tool/dies for each pipe/tube diameter with a specified, consistent CLR. The Rotary draw bending process is usually done on smaller pipe/tube sizes up to and including 10” in diameter and can be done on nearly most metals/alloys including but not limited to, aluminum, stainless and carbon steel. This process is accomplished by drawing the work piece (tube/pipe) around a rotating die. The leading edge of the material to be bent is clamped to the bend forming die and a mandrel is set within the tube/pipe at a precise location so as to support the work piece from within to avoid collapsing or failure of the tube/pipe. The forming die is than rotated, causing the tube/pipe to curve around the die leaving the work piece bent to a specific radius. This process for bending is the most common, least expensive and quickest but its drawback is the amount of costly tooling that is required to keep in house in order to perform many different bends.
The other most common manufacturing process to consider when looking to achieve short radius elbows, sweeps, and return fittings is heat-induction bending. Induction bending is most common but not limited to large diameter pipe/tubing, taking over where rotary draw bending left off at 10” in diameter all the way up to the largest pipe/tube sizes they make. This method of bending is extremely time consuming and a certain degree of metallurgy know how is required as this process heats up the work piece between 800 and 2,200 degrees through the use of an electrical transformer in the form of a coil to achieve the bend. These machines are generally very large in size and the overhead cost to operate and maintain these machines drives the product cost up. The main advantages of heat-induction bending is that these machines do not require specific sets of radius dies; heat-induction bending can perform an infinite number of differing radii and can do so with minimal distortion if any. The major drawback besides the cost of the products produced by this method, is the material alloy type that can be used in induction bending is pretty much limited to that of carbon steel alloys as the induction heating process requires a ferromagnetic material that will generate eddy currents within, when electromagnetic induction is placed upon it.