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Cold Bending and Hot Bending in Pipe Bending

Pipe bending is a crucial process in various industries, facilitating the creation of complex shapes and configurations essential for efficient piping systems. Understanding the techniques and methods involved in pipe bending is vital for achieving precise results and ensuring optimal performance. Two primary approaches to pipe bending, cold bending, and hot bending, offer distinct advantages and considerations, each suited to different applications and materials.

What is cold bending?


Cold bending of bending pipes
Cold bending of bending pipes

Cold bending is the plastic deformation of metals below the recrystallization temperature of the metal processing process (not using any added heat). In most cases of manufacturing, such cold forming is done at room temperature. In fact, it has two concepts, cold roll-forming, and cold bending.

  • Cold roll-forming: Sheets and strips of metal material are mechanically bent into profiles of a certain shape and size at room temperature. Its products are called cold-formed profiles. The advantages of cold roll forming are: it can produce all kinds of ultra-thin, ultra-wide, and complex shapes that cannot be produced by rolling; save metal materials; the mechanical properties of the products are good.
  • Cold bending: The stamping forming process of bending metal sheets, plates, and profiles into workpieces with a certain curvature, shape, and size at room temperature. Bending is widely used in the manufacture of high-pressure vessels, boiler drums, boiler tubes, hull steel plates and ribs, various utensils, instrumentation components, and cabinet inserts.
    Although the cold bending deformation is limited to a local area of ​​the material, the rebound effect affects the accuracy of the bending part. There are many factors that affect the springback, and these factors are difficult to control. The accuracy of the bending part caused by the Springbank has always been the key to cold bending production.

Top 4 types of cold bending

According to the process characteristics, cold bending can be divided into press bending, roll bending, rotary draw bending, and stretch bending. Read More: Profile and Section Bending: Bending Metal Profile 101

  • Press bending: Press bending is the most commonly used bending method. Most of the equipment used are general-purpose mechanical presses or hydraulic presses, and there are also special bending presses.
  • Roll bending: The commonly used roll bending equipment is the plate bending machine and angle roll/angle roller (aka, profile bending machine). The roll bending machine continuously bends metal profiles or plates according to the principle of three points to determine a circle or arc. Roll bending is a process whereby we obtain cold process deformation with a wider bend radius that theoretically can range from 5 times the cross-section to infinity. To achieve this process, the equipment used consists of plate bending machines.
  • Stretch bending: For bending parts with high precision requirements, larger length and radius of curvature, and smaller lateral dimensions, they can be stretched and bent on a certain stretch bending machine. During bending, the entire thickness of the plate is subjected to tensile stress, so only elongation deformation occurs. The deformation caused by a rebound after unloading is small, and it is easy to ensure accuracy.
  • Rotary Draw Bending: The mold of Rotary Draw Bending is installed on the main shaft; the workpiece is clamped by the clamping mold to prevent the workpiece from moving axially; the pressure mold is composed of a guide mold and a follow-up mold. On the wrinkle die, the movable die part moves with the workpiece when bending; the mandrel fills the inner cavity of the workpiece to prevent wrinkling, flattening, thinning, and other failures during bending. When the spindle rotates, the workpiece is wound around the bending die to be formed with the rotation of the spindle. Then the workpiece is fed, the space corner is ready for the next bending, and so on. The radius of the bending die determines the bending radius. If you want to get a different bending radius, just replace the bending die with a different radius.

Pros and Cons

  • Pros: No heating required; Better surface finish obtained; Superior dimension control; Better reproducibility and interchangeability of parts; Improved strength properties; Directional properties can be minimized.
  • Cons: Higher forces required for deformation; Heavier and more powerful equipment required; Less ductility available; Metal surfaces must be clean and scale-free; Strain hardening occurs (may require intermediate anneals); Imparted directional properties may be detrimental; May produce undesirable residual stresses

Before bending pipes and tubes

Pipe bending basics

  • Bent pipes and tubes offer numerous advantages in various industrial applications. One key benefit is their ability to minimize pressure changes while effectively routing materials through complex piping systems. This feature is crucial for maintaining efficient flow and preventing unnecessary strain on the system.
  • Moreover, the wide range of available pipe bend sizes and materials makes them suitable for handling diverse substances, including hot liquids, caustic chemicals, and high-viscosity fluids with suspended solids. For example, bent pipes are commonly used in Oil Sands slurry lines, where they facilitate the transportation of materials containing high concentrations of silica sand.
  • In addition to their versatility, bent pipes are also cost-effective solutions. By choosing the appropriate length and sizing for the specific application, companies can minimize expenses without compromising performance or reliability.
  • Furthermore, implementing bent pipes into processing systems is typically straightforward. Since most pipe bending methods do not alter the ends of the piping, they can be easily integrated using standard welding techniques, flanges, or other connection methods. This ease of implementation further enhances the appeal of using bent pipes and tubes in industrial settings.

Hot bending and cold bending methods for pipe bending

Hot bending pipe

Hot bending and cold bending are two primary techniques used in pipe bending, each with its own advantages and limitations. Hot bending involves heating the pipe to a high temperature before bending, which reduces the force required and allows for greater flexibility in shaping the pipe. On the other hand, cold bending does not involve heating the pipe and relies on physical force to achieve the desired bend.

The choice between hot and cold bending depends on various factors, including the type of material being bent and the angle of the bend required. Hot bending is typically preferred for materials that are more difficult to bend or require precise shaping, while cold bending is suitable for simpler bends and materials that can withstand the physical stress.

Cold bending of pipes

Roll Bending Pipe

Cold bending is a method of bending pipes without the use of heat. This process involves wrapping the pipe around a die or shape to achieve the desired bend. Unlike hot bending, cold bending does not require the pipe to be heated beforehand.

Cold pipe bending is the standard method for bending workpieces, typically performed without the need for added heat. Exceptions include situations involving extremely thick sheet metal or tight bending radii, where heating may be necessary to reduce bending forces and prevent material brittleness caused by low temperatures.

Compared to hot bending machinery, cold bending equipment is generally more cost-effective due to its simpler design. This affordability makes cold bending an appealing choice for smaller companies looking to minimize expenses while still achieving precise bends in their workpieces.

Pros and Cons

  • One of the main advantages of cold bending is its efficiency. The procedure is fast and does not require any additional cooling or special treatment after bending. Additionally, the equipment used for cold bending is generally affordable, making it a viable option for smaller companies with limited budgets or those that do not specialize in bending.
  • However, cold bending does have limitations. It is not suitable for achieving radical bends, as this can cause the pipe to crease or break. In such cases, filler material like sand may need to be used to prevent damage to the pipe. Despite these limitations, cold bending remains a practical solution for companies that require occasional bending and do not need extreme bends.

Most Common Pipe Bending Methods and Machines

CNC Roll Bending
Rotary Draw Bending
3D Freeform Bending
Stretch Forming
  • Rotary Draw Bending: A pipe or tube is bent using a combination of dies and other various components working in a rotary action. This action draws the pipe or tube forward making the desired bend. Rotary draw bending can also utilize mandrels.
  • Roll Bending: Used when large radius bends or curves are required, this method passes a piece of pipe or tube through a series of three rollers in a pyramid configuration to achieve the desired curve.

More cold-bent pipe methods and machines

Hot bending

hot pipe bending machine
hot pipe bending machine

Hot bending generally refers to different types of induction bending. Hot bending is highly effective at bending pipes because they are fast, precise, and make few errors.

The induction bending process, also known as high-frequency bending, incremental bending, or hot bending, uses inductors to locally heat steel by induction. This results in a narrow heat band in the shape to be bent. The shape is firmly held by a clamp at the desired radius, which is mounted on a free pivoting arm. The shape is pushed through the inductor by an accurate drive system which causes the hot section to form the induction bend at the set radius. The bent part is then cooled by water, forced or still air to fix the bent shape.

Hot bending of the pipe bending

Hot bending is generally only referring to different types of induction bending.

Induction bending is a highly effective way of pipe bending, as it is fast, precise, and with few errors. The induction bending process is performed by heating a certain point of the pipe up to where it then can be bent without much effort. It doesn’t require any filler material and the result of the bending tends to keep distortion to a minimum.

Many induction benders have also chosen this type of bending because of its energy sufficiency. After the heating process has been done, the bending doesn’t take a lot of time at all.

Features of pipe bending for Hot bending

Induction bending is a very effective method of pipe bending because it is fast, accurate, and almost error-free.

The induction bending process is performed by heating a certain point of the pipe, which can then be bent effortlessly. It does not require any filling material, and the result of bending tends to keep deformation to a minimum.

Many induction bending machines also choose this type of bending because of its sufficient energy. The heating process is the most time-consuming element of the process, after the heating process is completed, bending does not require much time at all.

Advantages of hot bending of pipe bending

Hot bending has the incomparable adaptability of cold bending.

  • For example, the straight line distance between two adjacent elbows on a pipe can be kept small, and even continuous bending can be carried out without leaving straight pipe sections;
  • Can process materials with poor cold ductility into elbows;
  • It can process elbows that require a lot of mechanical energy during cold bending and can bend brittle materials that are easy to break during cold bending. Hot bending can be bent into a small radius elbow on the pipe.
  • For carbon steel pipes and most alloy steel pipes, the bending radius of hot bending is much smaller than that of cold bending, and the bending radius can be as small as 0.7 to 1.5 times the outer diameter of the pipe.

Disadvantages of hot bending

  • The downside of hot bending may be that the material must be cooled later, increasing the time spent on each pipe, and the machines tend to be more expensive than cold bending equipment.
  • The negative aspects of hot bending can be that the material does have to cool off afterward, adding to the time spent on each pipe and that the machines tend to be more expensive than cold bending appliances.
  • The equipment is complex, the processing cost is high, the production efficiency is low, and the surface finish is poor.
  • For copper pipes, the cold bending process is used, which eliminates the possibility of “hydrogen disease” due to the elimination of high-temperature heating.

Induction Pipes and tubes Bending

Hot bending or induction bending:
While there are slight variances to different hot pipe bending methods, nearly all are a form of induction bending.

This method precisely heats the pipe using an induction heating coil before applying pressure to make the intended bend.

It requires much less physical force than cold bending methods and can produce bends of similar or higher quality with no filler materials, mandrils, or other additions used to avoid distortion.

What is Induction Bending?

Induction Bending is a precisely controlled and efficient piping bending technique. Local heating using high frequency induced electrical power is applied during the induction bending process. Pipes, tubes, and even structural shapes (channels, W & H sections) can be bent efficiently in an induction bending machine. Induction bending is also known as hot bending, incremental bending, or high-frequency bending. For bigger pipe diameters, when cold bending methods are limited, Induction bending is the most preferable option. Around the pipe to be bent, an induction coil is placed that heats the pipe circumference in the range of 850 – 1100 degrees Celsius.


Induction bending offers numerous advantages, including cost efficiency, faster production, and reduced welds in systems. It allows for the replacement of elbows with larger radius bends, reducing friction and wear. Induction bends are stronger than elbows with uniform wall thickness and require less non-destructive testing. Additionally, they minimize the risk of wall thinning and deformation, even with thin-walled pipes. The process produces precise bends with no wrinkles, using only straight pipe without the need for bend dies or mandrels. It is a clean process, requiring no lubricants, and enables diverse bending of various materials. Overall, induction bending provides a versatile, efficient, and cost-effective solution for bending applications across industries.


Induction bends are primarily utilized in pipeline systems for transporting liquids and gases. They are also prominent in applications necessitating large diameter bends with precision and reliability, particularly in industries requiring laminar smooth flow. Common sectors benefiting from induction bends include petrochemical, chemical, power generation (both conventional and nuclear), oil and gas (including expansion joints), compressor and pump stations handling fluids and gases, offshore operations, shipbuilding, and construction. These industries rely on the versatility and efficiency of induction bends to meet their diverse bending requirements, ensuring optimal performance and durability in their respective applications.

Induction Bending Materials

Induction bending technology offers versatility in bending various materials, provided they can be heated by induction. Common material groups suitable for induction bending include carbon steels, low alloyed steels, high alloyed steels, and fine-grain steels. Stainless steels, including austenitic, martensitic, ferritic, and duplex grades, are also compatible. Additionally, special alloys, clad pipes, aluminum, and titanium can be effectively bent using induction technology. This wide range of compatible materials makes induction bending a preferred choice for diverse industrial applications requiring precise and reliable bending of different materials.

Cold Bending vs. Hot Bending

  • Cold Bending: Cold bending is a plastic deformation process performed at room temperature, without the application of added heat. It encompasses both cold roll-forming and cold bending techniques. Cold roll-forming involves mechanically bending metal sheets and strips into profiles of specific shapes and sizes, offering versatility and material savings. Cold bending, on the other hand, utilizes stamping forming processes to bend metal sheets, plates, and profiles into workpieces with precise curvature and dimensions. While cold bending offers efficiency and cost-effectiveness, factors such as springback can affect bending accuracy.
  • Hot Bending: Hot bending, also known as induction bending, is a highly efficient technique that involves heating the pipe to a high temperature before bending. This method reduces bending forces and allows for greater flexibility in shaping the pipe. Induction bending utilizes induction heating coils to locally heat steel, enabling precise bending with minimal distortion. Despite its advantages, hot bending requires cooling after the bending process and may involve higher equipment costs.

Comparison and Applications

Cold bending offers benefits such as better surface finish, superior dimension control, and improved strength properties. It is suitable for smaller bends and materials with high ductility. In contrast, hot bending provides adaptability for complex bends and materials with poor cold ductility. Both techniques find applications across various industries, including petrochemical, power generation, and construction, where precision bending is essential for efficient operations.


Mastering the techniques of cold and hot bending is essential for professionals working in industries reliant on precise piping systems. By understanding the principles and applications of each method, practitioners can optimize their bending processes, minimize errors, and achieve superior results. Whether cold bending for efficiency and cost-effectiveness or hot bending for adaptability and precision, choosing the right technique is critical for ensuring the integrity and performance of piping systems across diverse applications and materials.