Manufacturers of seamless pipes use heat treatment to improve the qualities of the raw materials and the end products. For raw materials, most manufacturers use stainless steel, steel alloy, carbon alloy, titanium, etc. These metals are known for their corrosion resistance and strength.
Manufacturers heat the raw materials to a suitable temperature based on where the pipes will be used. Then, as the next heating steps are crucial, manufacturers must follow the proper processes to cool down the heated steel billets using different cooling methods. There are different heat treatments that the manufacturers follow. These include annealing, normalizing, tempering, quenching, chemical, and vacuum heating.
Heat treatment enhances the natural properties of stainless steel and other metal alloys the manufacturers choose to use. Apart from improving the efficiency of the seamless pipes, heating also gets rid of any impurities and improves the quality of the steel and metal alloys. Since the metals must be heated to a specific temperature without melting them, manufacturers must choose high-grade base materials instead of their cheaper alternatives.
Let us take a look at the primary heating processes that most manufacturers follow to produce seamless tubes and pipes:
Annealing is the most used heat treatment method that almost every manufacturer uses. In this process, pipe producers heat the metals to a higher temperature than their critical temperature. As a result, the metals reach the recrystallization stage, but manufacturers do not allow the metals to melt.
Annealing allows the seamless pipe manufacturers to remove any impurities that may have been a part of the metal in its raw stage. First, they hold the metals in high heat for a period of time so that the thick metal bars have no effects of their prior cold treatment. Later, manufacturers cool down the metal in a controlled environment. Different annealing processes exist, such as isothermal, recrystallization, diffusion, spheroidizing, stress relief, and complete and incomplete annealing.
Normalizing is another process of heating stainless steel and steel alloy. The process is also known as normalization. In this process, the pipe producers heat the seamless pipes to a temperature over 40~60°C. In some cases, they increase the heat to even higher so that it goes beyond the critical point.
It allows the manufacturers to achieve homogenization of the structure and complete austenitization. In this process, manufacturers air-cool the heated metal on an air-cooling bed. However, in this process, the manufacturers use flowing air to quicken the cooling process. In comparison with the annealing process, the normalizing method ensures the fine material structure of the seamless pipes, a short production cycle, better mechanical properties, low cost, and high equipment utilization rate.
Most manufacturers use the quenching process to treat seamless tubes and pipes. The manufacturers heat the pipes to a suitable temperature and then cool them down rapidly by submerging them in a quenching solution. Generally, pipe producers use oil or water to quench the heated metal. Sometimes they may use air cooling as well.
Quenching hardens metal pipes by changing their chemical and physical properties, including corrosion resistance, improved electrical conductivity, and magnetic properties. As a result, the hardened steel pipes are much stronger than their cheaper alternatives. Pipe fabricators use quenching methods such as single-liquid, double-liquid, isothermal, or fractional quenching. Based on the performance seamless pipe manufacturers expect from the pipes, they use a specific quenching method. Each method has its outcome.
After quenching, sometimes, the manufacturers want to change the composition of the metal pipes even more. Hence, they proceed with tempering. In this method, pipe manufacturers heat the metal pipes once again. But this time, they do not allow the temperature to reach beyond the critical point. Instead, they hold the pipes at the same temperature for a while before cooling them to room temperature using air cooling.
Manufacturers follow the tempering method only after quenching or other heat treatment. Tempering improves the malleability of the pipes while hardening them even more so that the pipes and tubes can withstand tremendous pressure. Also, tempering stabilizes seamless pipes that may have stress caused by quenching.
However, the manufacturers must cool down the pipes slowly. Fast cooling can make the metals brittle.
Heat treatment is an unavoidable procedure that the manufacturers of seamless tubes and pipes must follow. Heating raw metals to a specific temperature improves their strength, makes them more malleable, eliminates imperfections, and stabilizes metal pipes.
There are different heating methods that different pipe manufacturers use. However, there are some methods that are more common, and almost all pipe fabricators follow these methods. The heating methods include annealing, normalizing, quenching, and tempering. Each heating method has benefits.
Seamless pipes are known for their strength and durability. The features are connected with how well the pipes have been heat-treated. Hence, it is an essential step in manufacturing seamless tubes and pipes.