Different Methods of Manufacturing Seamless Tubes and Pipes 

Have you ever wondered which type of pipes you should invest in for your industry? While some of you may choose conventional welded pipes, others choose seamless pipes. Even though seamless pipes are not new, more and more people are realizing their potential.  

Earlier, people did not invest in seamless tubes and pipes because of their price. Welded piping solutions are less costly than seamless ones. However, when industries realized that seamless pipes last much longer than welded ones, they started to invest in these pipes.  

There are different manufacturing processes for producing seamless pipes. The primary two methods are hot rolling and cold drawing. Let us explore the two processes to understand how manufacturers prepare them.  

Hot-rolled seamless pipes: 

Hot rolling is a popular method of producing seamless pipes, especially for pipes with larger diameters and thicker walls. The hot rolling process involves heating a steel billet to a temperature above its recrystallization point, typically around 1,100 °C. Manufacturers then pass the billet through a series of rollers, which compress the steel and shape it into a pipe. 

• Preparation of raw materials: 

Preparing the raw materials is the first step in producing hot-rolled seamless pipes. The raw materials the producers use for hot rolling seamless pipes are steel billets. Steel billets are made from ingots cast in a continuous casting machine. Pipe fabricators then heat the solid bars in a furnace to a temperature of around 1,200 °C, which makes them more malleable and easier to work with. 

• Heating the billets: 

Once pipe producers prepare the billets, they can heat them to a temperature above their recrystallization point. The recrystallization point is the temperature at which the steel becomes soft and pliable, making it easier to shape. Manufacturers must heat the billets in a furnace to the desired temperature, typically around 1,100 °C. 

• Piercing: 

The next step in the hot rolling process is piercing. Seamless pipe manufacturers pass the steel billets through a piercing mill. A piercing mandrel is a machine that drills a hole through the center of the billet. It creates a hollow tube, which will become a seamless pipe. 

• Rolling: 

After piercing, pipe fabricators pass the billet through rollers that gradually shape it into a pipe. They arrange the rollers in pairs, each rotating in opposite directions. As the billet passes through the rollers, it is gradually compressed and elongated until it reaches the desired diameter and wall thickness. Properly rolling the pipes ensures that manufacturers meet the required dimensions for seamless tubes and pipes 

• Sizing and straightening: 

Once engineers achieve the desired shape of the rolled pipe, they can pass it through a sizing mill, which is a machine that ensures the pipe has the correct dimensions. The sizing mill also straightens the pipe, ensuring it is free from bends or kinks. Hence, pipe fabricators have multiple sizing mills to increase productivity.  

• Cooling: 

After manufacturers complete sizing and straightening the pipe, they use a water spray to cool it down. It is essential as it ensures the pipe is strong and durable. 

• Cutting and inspection: 

Cutting and inspection are The final steps in the hot-rolled seamless pipe manufacturing process. Pipe fabricators must cut the pipe to the desired length and inspect each section for defects or imperfections. It is when pipe operators should remove any defective sections, bundle the remaining sections, and prepare them for shipment. 

Cold-drawn seamless pipes: 

Cold drawing is another method that manufacturers use to produce seamless pipes. Unlike hot rolling, which is ideal for larger and thicker walls, cold drawing is better suited for smaller and thinner walls. Cold drawing involves pulling a steel tube through a die, reducing its diameter and wall thickness. 

Preparation of raw materials: 

As with hot rolling, preparing the raw materials is the first step in the cold drawing process. The raw materials seamless pipe manufacturers may use for cold drawing are steel bars or billets. Steel bars or billets are made from ingots cast in a continuous casting machine. Pipe fabricators can heat the ingot casts in a furnace to a temperature of around 1,200 °C. It makes them more malleable and easier to work with. As a result, engineers effortlessly produce seamless tubes.  

Drawing: 

The next step in the cold drawing process is drawing. Manufacturers need to pass the heated steel bars or billets through a series of dies that gradually reduce their diameter and wall thickness. The dies are made from hardened steel and are designed to apply uniform pressure to the steel, ensuring that pipe producers can draw the pipes evenly. 

Annealing: 

Unlike producing hot-rolled seamless pipes, manufacturers must anneal cold-drawn tubes to improve their properties. Annealing involves heating the steel to a high temperature and cooling it slowly. This process relieves any internal stresses that may have developed during drawing and makes the steel more ductile. 

Sizing: 

After annealing, engineers can pass the steel tube through a sizing machine to ensure it has the correct dimensions. The sizing machine uses a series of rollers to stretch and compress the steel tube until it has the desired diameter and wall thickness. 

Straightening and cutting: 

After pipe operators size the tubes, they straighten them using a straightening machine. It allows them to remove any bends in the tubes. Also, this is when engineers cut the tubes to their desired length.  

Inspection and testing: 

The final step in the cold drawing process is inspection and testing. All seamless tubes and pipes need proper inspection so manufacturers can detect defects or imperfections. Also, the inspection process allows them to take samples for testing. While some pipe fabricators use destructive testing, such as tensile strength testing, some prefer non-destructive testing, such as ultrasonic testing.