The Basics of Pipe and Tube Bending
Pipe and tube bending is a fabrication method used to form metal tubes by bending them into desired angles and shapes. Bending pipes and tubes allows for the fabrication of complex structures and piping systems that are integral to everything from musical instruments and handrails to mechanical parts, air conditioning equipment, plumbing, and much more. Pipe and tube fittings come in the form of bent tubes, which enable fabricators to change the direction of conduits for fluids and gases in exhaust systems, hydraulic lines, pipelines, etc. So far, so good, right? The basics are pretty simple, but when planning commercial and industrial mechanical and fabrication projects, there are some key details and considerations that may help make important choices about materials, methods, and processes.
This article contains all the basics of tube and pipe bending. Keep reading to learn more about:
- Metal Pipe vs. Metal Tube
- The Purpose of Pipe and Tube Bending
- What Is a Bend Radius?
- Common Pipe and Tube Bending Methods
- The Basic Pipe and Tube Bending Process
- Get Expert Support from a Pipe and Tube Bending Specialist
Metal Pipe vs. Metal Tube
Metal pipe is typically supplied and fabricated from steel and most alloys from aluminum, stainless steel, nickel, and even exotic alloys such as titanium and zirconium. It is commonly produced in larger sizes with thicker walls than tubing and less stringent specifications for dimensions, finishes, chemical composition, and mechanical properties.
Metal tube is typically supplied and fabricated from steel, stainless steel, brass, copper, and aluminum but is made from many other alloys, too. Metal tube is generally lighter than pipe and easier to form with the appropriate equipment, and can be bent and formed into more complex shapes without the need for elbows or fittings.
The outside diameter (OD) of tubing is the nominal size, whereas the OD of pipe varies and is not equal to the nominal size. The heavier wall thicknesses of pipe allow for threaded ends for joining lengths with couplings or screwed fittings. A large portion of pipe is also used without screw threads, where lengths are joined or fittings attached by welds or other means.
The Purpose of Pipe and Tube Bending
Pipes and tubes have many uses and are primarily used to safely and efficiently transport water, liquids, gases, and chemicals for various utilities and functions in homes, schools, businesses, industrial, commercial, and manufacturing facilities. Pipes and tubes have higher structural integrity than many other metal shapes. But straight tubes aren’t usable for many purposes within a building, so they often need to be shaped and bent at different angles. Depending on the project, complex bending solutions may even eliminate many fittings.
Tube bending is not limited to any particular metal, and various metals and alloys are used for their unique attributes. There are many different options for how pipes and tubes are bent and formed to suit all types of unique needs. Each method comes with advantages, disadvantages, and costs.
What Is a Bend Radius?
Pipe bends are classified according to the bend’s centerline radius (CLR) as a ratio to the nominal pipe diameter. For example, 4” NPS pipe bent on a 6” CLR is classified as a 1½D Bend (1½ times the nominal pipe diameter). When bent on a 12” CLR, the bend is classified as 3D.
Most cold bends are made on a 1½D radius. The primary reason for choosing 1½D is that it is interchangeable with long radius butt weld elbows (a 4” Long Radius 90° Elbow is 6” center-to-end). As a result, the design does not need to be changed to permit bending. A standard weld fitting can be used when modifying an existing formed system or vice versa.
As an alternative to 1½D bending, when flow restriction may be a concern, 3D bend radii may be utilized. Studies have also indicated potential energy savings using larger bend radii. 3D Bending may require special design consideration
Common Pipe and Tube Bending Methods
There are four basic processes for pipe and tube bending. All four are standard for all pipe and tube materials and diameters. The most significant factors in determining which method would work best are your required wall thickness, desired radius, and configuration of the finished part.
Rotary Draw Bending
Rotary draw bending is a versatile process involving clamping the exterior of a pipe and bending it over a die with the desired radius of your pipe or tube. This method is effective for bending applications requiring a tighter radius because the die helps prevent the tube from deforming into an oval shape during bending. Clamping pressure must be carefully maintained during the process to avoid exterior wrinkling and ensure the extrados does not become too thin. Choosing the right materials and maintaining a consistent clamping pressure helps prevent these issues.
Ram Bending
A simple and inexpensive method of pipe and tube bending, ram bending involves driving a hydraulic ram into short segments of pipe that are braced against a pivot block or roller. The pipe is shifted, and the process is repeated in multiple locations to achieve the desired radius. Ram bending offers limited control and lacks some of the precision needed for applications demanding tight tolerances.
Compression Bending
Compression bending is similar to rotary draw bending. This process involves clamping a tube, then pulling it around a die to create the desired radius. This process doesn’t have the same controls as rotary draw bending and isn’t recommended for close tolerances.
Roll Bending
Roll bending forms pipes and tubes into bends using equipment that features two immobile rollers and a moving inner roller. The rollers are situated in a pyramid formation, with the two immobile rollers holding the pipe secure as the moving roller presses into the metal to create a bend. After bending one section, the operator rotates the material to bend a new section and repeats the process until the desired radius is achieved. Roll bending is typically used for construction applications involving a larger radius or to create spiraled pipes like heating and cooling coils.
The Basic Pipe and Tube Bending Process
Step 1. Think About What you Need your Pipe or Tube to do
Before beginning any pipe or tube bending project, the first step is to think about what you need your product to do. Ask yourself these questions:
- Does your application require a heavy or light material?
- Does the material need to be resistant to rust or corrosion?
- Does the material need to conduct thermal energy?
You’ll also need to consider the inside diameter (ID) and outside diameter (OD) of your pipe or tube. The ID and OD determine wall thickness, which dictates the bend radius your pipe or tube can handle. As a pipe or tube is bent, the outside radius stretches, thinning the material. If a wall is stretched too thin, the tube or pipe will collapse into an oval shape, potentially affecting the functionality of the tube, especially in precision applications. To prevent this issue, you need to ensure the wall thickness is sufficient for the radius you’re bending. One other consideration is the Center Line Radius (CLR) – the distance between the center of the curve and the centerline of a pipe or tube. The CLR you want to achieve will be a factor in determining which bending process makes the most sense.
Step 2. Set Up the Tube Bender
Pipe and tube bending equipment can be tooled for the size of pipes and tubes you are using. The bending equipment has mechanical and hydraulic adjustments that assist the operator in producing quality bends. When using a CNC software-controlled tube bender, software helps make these adjustments as precisely as possible.
Step 3. Align the Tube
Align the pipe or tube on the bender properly. Use the mandrel and wiper dies in the right places as required. Generally, the benders come with a protractor to measure the bend angle.
Step 4. Bend the Tube
Follow the guidelines that come with your pipe or tube bender and begin the bending process. Directions between bending equipment can vary, so ensure you’re referring to your particular model’s guidelines.
Step 5. Disengage the Parts
Disengage the pipe or tube from the bender along with other equipment like dies and wiper dies. Operators must always be cautious about safely removing the pipe or tube as the springback and other factors come with the risk of injury.
Get Expert Support from a Pipe and Tube Bending Specialist
Whether it’s chemical lines at a manufacturing plant, gas lines for a hospital, commercial plumbing, or any other type of tube or pipe project, having a pipe and tube who is passionate about providing high-quality products fast can be hard to come by. When selecting a pipe and tube bending partner, look for someone who understands your industry and takes time to understand your unique situation. This type of partnership can deliver an incredible advantage that can have a significant impact on your bottom line.
APEX leads the industry in close-radius pipe bending and lap-joint flaring, including high nickel alloys and titanium. Our equipment bends and forms pipe, structural steel, and plate for numerous applications. Our tube and pipe bending and flaring capabilities eliminate costly welding operations and provide piping with higher integrity, faster fabrication, and lower NDT costs. Through our constant investment in advanced technology, our craftsmen are experienced working with the latest, cutting edge, and specialized equipment in the industry. In addition, APEX manufactures Type C stub ends—the lowest installed cost flange connection available anywhere in the world. Contact us today to talk to a specialist.