We Super Steel Manufacturing Co.,Ltd(SMC) are amongst the top manufacturers and suppliers for the seamless steel pipe, welded steel pipe, OCTG products and fittings from China. We have been manufacturing and supplying these products to the industry since 1993, and received repeat orders and appreciation from our valued customers.
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Always up to date. In this column you can find the steel pipe related articles, including industry trends, product standards and materials, and some technical guidelines.
Seamless steel pipes, with a hollow cross-section and no seams, are a critical component in many industries due to their strength and reliability. The manufacturing process involves transforming a solid steel billet into a hollow tube through methods like perforation and rolling, which eliminates the potential weaknesses associated with welded seams. Temperature plays a significant role throughout the lifecycle of seamless steel pipes, affecting everything from production to operation and heat treatment.
Heating Temperature During Production of Seamless Steel Pipes
The production of seamless steel pipes typically involves hot rolling or cold drawing (cold rolling). In the hot rolling process, the tube billet must be heated to high temperatures for piercing and rolling.
- Heating Temperature Range:
For hot-rolled seamless steel pipes, the typical heating temperature ranges between 1100°C to 1300°C. However, this can vary depending on factors such as the type of steel, pipe size, and specific rolling process. For example, when producing stainless steel seamless pipes, the heating temperature is usually around 1204°C (2200°F).
- Heating Method:
Common methods of heating include ring heating furnaces and walking beam heating furnaces. These furnaces must ensure uniform temperature distribution to avoid defects in the subsequent rolling process. Uneven heating can result in material inconsistencies that impact the quality of the final product.
- Importance of Temperature Control:
Proper control of the heating temperature is essential for maintaining the quality of seamless steel pipes. If the heating temperature is too high, defects such as coarse grains and overburning may occur. Conversely, if the temperature is too low, it can lead to increased deformation resistance, making the rolling process difficult and inefficient.
Working Temperature During the Use of Seamless Steel Pipes
Once produced, seamless steel pipes are used in various environments, and their operating temperature depends on the material and intended application.
- General Seamless Carbon Steel Pipes:
These pipes are typically used in environments with room temperature or lower temperatures.
- Alloy Steel Seamless Pipes:
Alloy steel pipes can withstand higher temperatures and pressures. For example, high-pressure boiler pipes are designed for operating temperatures above 500°C. These pipes are essential in manufacturing the heating surfaces of high-pressure water tube boilers.
- Stainless Steel Seamless Pipes:
Stainless steel is known for its excellent high-temperature resistance. However, it may experience intergranular corrosion within the temperature range of 450°C to 860°C. This occurs when carbon dilutes the chromium content in the steel, forming chromium-poor zones that alter its properties. Therefore, choosing the appropriate grade of stainless steel is crucial for ensuring durability in high-temperature environments.
- Seamless Steel Pipes for Low-Temperature Applications:
For low-temperature environments, such as pipelines transporting liquefied natural gas (LNG), seamless steel pipes are designed to withstand extreme conditions. These pipes can operate at temperatures as low as -196°C, as specified by standards such as GB/T18984-2003, which covers low-temperature pressure vessel and heat exchanger pipelines.
Temperature Control During Heat Treatment of Seamless Steel Pipes
To enhance the mechanical properties or relieve internal stress, seamless steel pipes often undergo heat treatment during or after production. Different heat treatment processes require specific temperature control.
1. Annealing:
In this process, the steel pipe is heated to an optimal temperature, held for a period of time, and then slowly cooled. This process reduces hardness, relieves internal stress, and improves the pipe's plasticity and toughness.
2. Normalizing:
The steel pipe is heated above the critical temperature and then air-cooled. This process refines the grain structure and improves mechanical properties. The normalizing temperature range typically falls between 727°C to 912°C, or about 30–50°C above the critical temperature of austenite.
3. Quenching:
Here, the steel pipe is heated to above the critical temperature and rapidly cooled (usually in water or oil) to achieve high hardness and strength. This process enhances the material's wear resistance but can make it more brittle.
4. Tempering:
After quenching, the steel pipe is reheated to a lower temperature, held for a period, and then cooled. This process reduces brittleness and improves the toughness of the pipe.
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