Producing Hot-Rolled and Cold-Rolled Seamless Pipes in Manufacturing Facilities

Manufacturers produce hot-rolled seamless pipes and tubes using a heating process. They forge the pipes in the fire. They source solid steel billets or slabs and heat them. Generally, pipe fabricators choose stainless steel, carbon alloy, and other hard metal billets to produce these pipes and tubes. Line pipe suppliers use incredibly high temperatures to heat these metal slabs before they can drill them.  

The temperature in the hot-rolling process can reach up to 1000° C or 1832° F. The metal billets turn red, which means that they have become malleable. At this stage, the metal slabs are ready for piercing, which gives them their cylindrical shape.  

The journey starts in a steel mill, where engineers melt down raw materials in a furnace. Thus, they create a molten pool of metal. Then, they cast this molten metal into solid rectangular shapes. These shapes are what we call billets. These billets become the foundation for the hot-rolling process. 

Once seamless tube manufacturers cast this billet, it is time to wind up the heat. They place the billet into a reheat furnace, bringing it to the necessary temperature for rolling. Such high temperature is necessary to eliminate imperfections and inclusions from the billet. At the same time, such high heat makes the metal more malleable to ensure engineers can pierce them. Thus, pipe operators achieve the final product’s integrity. 

The red-hot billet is now ready for rolling. Manufacturers pass it through a series of rollers that gradually shape it into cylindrical pipes or tubes. Depending on the desired diameter and thickness, the billet may undergo multiple passes through these rollers. Line pipe suppliers reshape the metal using such high heat and pressure. Thus, they can reduce the thickness and increase the length of the pipes. Formation of the pipes is one of the most vital steps in the hot-rolling process, as it can determine the strength of the pipes.  

As the pipe or tube takes shape, it is critical to cool it quickly to set the desired properties. Water sprays or air cooling mechanisms help to cool the material rapidly. Sometimes, manufacturers use other cooling materials, such as brine, oil, etc., to cool down the pipes. Different cooling mediums give different results in terms of strength, hardness, and uniformity. Simultaneously, engineers size the newly formed pipe or tube according to precise measurements and standards. 

Unlike cold-rolled seamless pipes, hot-rolled pipes may still have some bends and irregularities after cooling down. To rectify this, it goes through a straightening process. The final step involves cutting it into the required lengths. The process often involves sawing, ensuring the pipe or tube meets the necessary length specifications. 

No hot-rolled pipe or tube leaves the facility without undergoing rigorous inspection. Skilled technicians examine the product for defects, cracks, or inconsistencies, ensuring it meets industry standards. The quality control step is crucial for safety and performance in various applications. 

Cold-rolled pipes and tubes:  

While manufacturers shape hot-rolled pipes and tubes under intense heat, they craft cold-rolled ones at much lower temperatures. Cold rolling offers more precision and control with several other advantages. 

Seamless tube manufacturers form the mother tube using the hot rolling process. These pipes undergo a size reduction process. Then, they draw the mother tube over a mandrel (using a cylindrical object to shape the inner surface). They create the desired shape and dimensions. We call the process cold drawing. 

Cold-drawn tubes have exceptional dimensional accuracy and surface finish. However, they tend to be quite hard and brittle. To enhance their mechanical properties, the tubes go through an annealing process. Annealing involves heating the tubes to a specific temperature, followed by a controlled cooling process. The process softens the material, making it more malleable and workable. 

After annealing, the cold-drawn seamless tubes may undergo additional processes like straightening and cutting to meet exact length and size requirements. These processes ensure the tubes are ready for their intended applications. 

The key differences between hot-rolled vs. cold-rolled pipes:  

While hot-rolled and cold-rolled pipes and tubes serve many purposes, the two manufacturing processes have distinct characteristics and advantages. 

Both types of pipes matter: 

Pipes and tubes are essential in our daily lives. They serve a variety of requirements. Seamless pipes, specifically, ensure safety while transporting water, oil, gas, and steam. The manufacturing process of these pipes and tubes makes a difference in their appearance, costs, strength, and dimensional precision.