Tube & Pipe Bending Information

Basic Facts and FAQs

Pipes and tubes are both tubular products, intended primarily for the conveying of water, fuel, gas, air, and steam. Metal pipes and tubes can also be used structurally in construction, as columns and railings. 

Pipe & Tube Construction Basics

There are two types of pipe and tube construction and each comes with their own advantages and disadvantages.

• Welded (Seams): Welded tube is produced from a strip that is roll formed and welded to produce a tube. With a seam on the outside and a weld bead on the inside, use this tubing when your application does not require a smooth interior. For some tubing, the weld bead is smoothed (also known as drawn), which reduces the chance of particle buildup and makes it an economical alternative to seamless tubing. Welded tube is considerably less expensive than seamless tube and is readily available in long continuous lengths.
• Extruded (Seamless): Seamless tube is extruded and drawn from a billet and has no weld, so it is smooth on the inside to reduce the chance of particle buildup. The working pressure of a seamless tube is 20% greater than welded tubing, has greater corrosion resistance and can be flared without splitting along the seam.  

What is the Difference Between Metal Pipes and Metal Tubes?

Bending is performed with both metal pipe and metal tubing, however there are distinct differences between the two that determine bending capabilities as well as whether finishing applications such as threading can be applied. The choice of metal piping versus metal tubing is also determined by the material your application requires.

Metal Pipe

Metal pipe is fabricated from steel and aluminum. It is commonly produced in greater quantities than metal tubing and in relatively few standard sizes.

• Generally made to less exacting specifications for dimensions, finish, chemical composition, and mechanical properties than tubing.
• Sizes and wall thicknesses of pipe were originally standardized to permit threading the end for joining lengths with couplings or other connectors.
• A large proportion of pipe is also used without screw threads (plain end), where lengths are joined together, or fittings attached, by welding or other means.

Metal Tubing

Metal tubes are fabricated from steel, stainless steel, brass, copper, and aluminum. It is lighter than pipe and easier to work with. Metal tubes can be bent into shape without the need for elbows or other fittings. Fittings are used to connect tubing to pumps, valves, and other components. 

Pipe and Tube Bending

While a generally straightforward tooling process, pipe and tube bending carries complications like flattening or collapsing due to thin walls, dimpling caused by poor or improper material choice, or wrinkling and crimping caused by misalignment and wall thinness. By understanding the material, bend radius and the various bending processes, you can help prevent issues that result in material damage and lost production time.

Prior to beginning any pipe or tube bending project, the first step is to think about what you need your product to do.

• Does your application require a heavy or light material?
• Does the material need to be resistant to rust or corrosion, or have the ability to conduct thermal energy?
• You will also need to consider the inside diameter (ID) and outside diameter (OD) of your pipe or tube; these measurements determine wall thickness, which will dictate the bend radius your pipe or tube is able to handle.

As a tube or pipe is bent, the outside radius stretches, which causes the material to thin. If a wall is stretched too thin, the tube or pipe will collapse into an oval shape, which could affect the functionality of the tube, especially in precision applications. To prevent this issue, you will need to ensure your wall thickness is sufficient for the radius you are bending. One other consideration is the Center Line Radius (CLR), which is the distance between the center of the curve and the centerline (axis) of a piece of piping or tubing. The CLR you wish to achieve will be a determining factor in which tube bending process is used. 

What Are the Different Processes for Bending Pipes and Tubes?

There are four basic process used for pipe and tube bending. All four processes are standard for various pipe and tube materials and diameters, but the configuration and radius of your finished part is a determining factor in which method would be best.

When choosing a bending method, the wall thickness and desired radius are the most significant factors. Tooling costs are also a consideration. To achieve the best results, it is recommended that the radius is 3X the tube or pipe diameter. Smaller radiuses are possible, but there can be complications, especially if the walls of your pipe or tube are too thin. The use of dies or mandrels can help prevent issues, but they also add to the cost of your production.  

Rotary Draw Bending

Rotary draw bending is a versatile process that involves clamping the exterior of a pipe, then bending it over a die with the same radius as the desired tube radius. This method works well for bending applications that require a tighter radius because the die helps prevent the tube from forming into an oval shape as it is bent. Clamping pressure must closely be monitored during the process to ensure no exterior wrinkling occurs and to ensure the material does not become too thin, which can result in collapse. Choosing the right material for the desired radius and maintaining a consistent clamping pressure can help prevent these issues.

Ram Bending

Ram bending is perhaps the simplest and most cost-effective method of pipe and tube bending. The ram bending process bends tubing by driving a hydraulic ram into short segments of pipe that are braced against a pivot block or roller. The pipe is then shifted, and the process is repeated in multiple locations until the desired radius is achieved. The simplicity of the ram bending process means there is less control, so it is not always the best process for pipe bending applications that require a tight tolerance.

Compression Bending

Compression bending is similar to rotary draw bending. This process involves clamping the tubing, then pulling it around a bend die to create the desired radius. This method is more limited that rotary draw bending and therefore should not be used for bending applications requiring a tighter radius.

Roll Bending

Roll bending utilizes two immobile rollers and a mobile, inner roller to form a pipe or tube into a bend. The rollers are in a pyramid formation, with the two immobile rollers holding the pipe secure as the mobile roller presses into the metal to create a bend. After one section of pipe or tube is bent, the material is rotated to bend a new section and the process is repeated until the desired radius is achieved. This method is typically used to for construction applications involving a larger radius or to create spiraled pipes such as cooling coils.

Dies and Mandrels

A series of dies are used for clamping and to create pressure or determine the bend radius during the tube and pipe bending process. There are also mandrels, which are components that support the interior of a tube to prevent collapse or wrinkling as the pipe is bent. Wiper dies may also be inserted into the tube or piping to prevent wrinkling. The need for a mandrel or additional dies is dependent upon your material, wall thickness and radius. Additional tooling can significantly increase the cost of your overall production, so it is important to discuss these items with your tube pending provider when you submit your design specs. 

Important Factors for Pipe and Tube Bending 

There are a few important factors to keep in mind when creating the design for your tube bending project, including pipe and tube material, wall thickness, Center Line Radius, and tolerances.

Tubing and Piping Materials

Materials are chosen for a range of reasons including durability, corrosion resistant and thermal conductivity. Common materials include:

• Aluminum: typically chosen for its weight and corrosion resistance
• Stainless Steel: offers corrosion resistance
• Steel: less costly than other materials but is not resistant to rust and corrosion.  
• Copper: is heat conductive and commonly used for heating and cooling applications, including laser cooling systems and household or commercial heating and cooling units. Aluminum piping and tubing is sometimes lined with copper to create heat transfer.

Wall Thickness

Wall thickness plays a significant role in determining the radius in which a pipe or tube can be bent. Each tubing OD comes in a variety of wall-thickness choices. As the walls get thicker, the amount of pressure the tubing can withstand increases and the amount of flow decreases. The thinner the wall, the more susceptible the pipe or tube is to collapse during the bending process.

Center Line Radius (CLR)

The center line radius should typically measure 2-3X the diameter of the tube, depending on wall thickness. It is possible to bend on tighter radius (up to 1X the diameter of the tube) with some materials, but not without more complex tooling. The tighter the radius, the more tooling required and the more expensive the part.

Things to consider when determining the center line radius include:

• Minimize tooling costs by using the same CLR for all bends unless prohibited by design restraints.
• Reduce overall costs by allowing 3X the diameter of the tube of straight for clamping between bends and from the edge of the tube. This reduces the overall cost of the part by reducing additional trim operations and increasing the bend rate.
• Clamping closer than 3X the diameter of the tube may require a more aggressive grip finish and/or compound tooling, which can increase production costs.
• The tighter the tolerance, the greater the cost. Keep production costs down by designing your pipe or tube with minimum tolerance needed for your product to properly function.
• Where possible, open all tolerances and deviate from engineering block tolerances when appropriate.

Tolerances

• The tighter the tolerance, the greater the cost. Keep production costs down by designing your pipe or tube with minimum tolerance needed for your product to properly function.
• Where possible, open all tolerances and deviate from engineering block tolerances when appropriate. 

Learn More About Tube and Pipe Bending

Contact Triad Products Corp. today to learn more about how we can assist you with your custom tube bending and tubular component manufacturing. Triad Products specializes in small to medium production runs, ranging in the 100's to 1000's.