Low-Temperature Brittleness Temperature of Carbon Steel Pipe

Low-Temperature Brittleness Temperature of Carbon Steel Pipe

The low-temperature brittleness temperature of carbon steel pipe is affected by a variety of factors, generally ranging from -29°C to -46°C. The specific temperature depends on factors such as carbon content, alloying elements, and cold treatment method.

Performance Changes of Carbon Steel Pipe at Low Temperatures

Carbon steel pipe undergoes significant changes in its properties in low-temperature environments. Normally, carbon steel pipe can function normally above -20°C, where the steel is in a ductile state, exhibiting excellent strength and toughness. However, when temperatures drop below -20°C, carbon steel pipe gradually enters a brittle state. In this state, the pipe becomes more fragile and susceptible to fracture due to impact.

In addition to reduced impact resistance, low temperatures also reduce the corrosion resistance, wear resistance, and hydrogen embrittlement resistance of carbon steel pipe. Therefore, special attention must be paid to the safety and reliability of carbon steel pipe when used in low-temperature environments.

Low-Temperature Brittleness of Carbon Steel Pipe

Carbon steel pipes can become brittle in low-temperature environments. This is due to the low temperature-induced transformation of ferrite and cementite in the steel, which leads to brittle fracture. The low-temperature brittleness temperature of carbon steel pipe is not a fixed value but rather influenced by a combination of factors.

Using Temperature Requirements for Carbon Steel Pipe in Low-Temperature

For low-temperature, low-stress applications, carbon steel pipe has certain operating temperature requirements. According to relevant regulations, low-temperature, low-stress conditions are considered when the ambient temperature is below -20°C and the tensile membrane stress is less than or equal to 1/6 of the standard room-temperature yield point and no greater than 50 MPa.

In this case, the lower operating temperature of carbon steel pipe can be reduced to -70°C. However, this does not mean that carbon steel pipe can be used unrestricted in all low-temperature environments. In practical applications, understanding the low-temperature use range of carbon steel pipe requires evaluation and selection based on specific circumstances.

Factors Affecting the Low-Temperature Brittleness Temperature of Carbon Steel Pipe

1. Carbon Content

Based on the carbon content, it can be categorized into three types: mild steel pipe, medium-carbon steel pipe, and high-carbon steel pipe. Carbon steel pipe with a high carbon content is more susceptible to brittleness at low temperatures. This is because carbon forms a large amount of cementite, increasing the brittleness of the steel.

2. Alloying Elements

The addition of alloying elements can improve the low-temperature performance of carbon steel pipes. For example, alloying elements such as nickel, copper, and cobalt can inhibit the transformation of ferrite to cementite, improving the steel's plasticity and toughness, thereby lowering the low-temperature brittle transition temperature.

3. Cold Treatment Methods

Appropriate cold treatment, such as quenching and normalizing, can improve the low-temperature performance of carbon steel pipes. By adjusting cold treatment process parameters, the steel's microstructure can be modified, thereby improving its low-temperature toughness.

Range of Low-Temperature Brittle Transformation Temperatures of Carbon Steel Pipes

Taking all the above factors into account, the low-temperature brittle transition temperature of ordinary carbon steel pipes is generally between -29°C and -46°C. Within this temperature range, carbon steel pipes can still meet general industrial requirements.

However, for specific applications, such as those in the liquefied natural gas (LNG) and liquefied petroleum gas (LPG) industries, specialized carbon steel pipes with lower brittle transition temperatures may be required.

Measures to Improve the Low-Temperature Performance of Carbon Steel Pipes

In addition to adjusting carbon content, adding alloying elements, and optimizing cold treatment methods, other measures can be taken to improve the low-temperature performance of carbon steel pipes.

For example, mechanical surface treatment can be used to improve the surface quality of the steel; lubrication and cooling systems can be optimized to maintain good performance at low temperatures; and more stringent control and testing methods can be implemented to ensure the safety and reliability of carbon steel pipes.

How to Safely Use Carbon Steel Pipes in Low-Temperature Environments

To safely use carbon steel pipes in low-temperature environments, the following recommendations are provided:

1. When selecting and using carbon steel pipes, factors such as impact resistance, corrosion resistance, wear resistance, and hydrogen embrittlement resistance should be fully considered. These properties can significantly change in low-temperature environments.

2. For carbon steel pipes intended for use in low-temperature environments, detailed material evaluation and selection should be conducted. If necessary, steels with alloying elements added to enhance low-temperature performance can be selected.

3. During the design phase, the cold insulation structure and support design for carbon steel pipes in low-temperature environments should be fully considered. This helps reduce energy loss, improve equipment efficiency, and ensure safe pipeline operation.

4. Regularly inspect and maintain carbon steel pipes used in low-temperature environments. Pay particular attention to the integrity of the pipe's insulation and check for corrosion, wear, and other issues.

Summary

Understanding the low-temperature embrittlement temperature of carbon steel pipes is crucial for ensuring their safe use in various industrial applications. Through appropriate material selection, optimized design, and regular maintenance, the service life of carbon steel pipes can be effectively extended and safety risks reduced.