The change in flexibility of metal hoses at low temperatures is a complex issue involving materials science, mechanical properties, and engineering applications. Its core mechanism stems from the alteration of the physical properties of metallic materials at low temperatures, which directly affects the hose's bending capacity, fatigue resistance, and overall reliability. The impact of low temperature on metal hoses is not singular but rather the result of the combined effects of changes in material microstructure, stress distribution adjustments, and external constraints.
A significant characteristic of metallic materials at low temperatures is cold brittleness, a phenomenon characterized by decreased toughness and increased brittleness. As the temperature decreases, the crystal structure of the metal contracts, and the interatomic bonding forces strengthen, making the material more susceptible to crack propagation rather than plastic deformation under external forces. This change manifests in metal hoses as an increased bending radius, increased bending resistance, and even a risk of fracture at extreme low temperatures. For example, the impact toughness of ordinary carbon steel may decrease by more than 50% below -20°C, while austenitic stainless steel, due to its face-centered cubic structure, can maintain high toughness even at lower temperatures.
The flexibility of metal hoses is closely related to their corrugated structure design. Corrugated structures absorb displacement and vibration through elastic deformation, but low temperatures alter their mechanical response. On one hand, low temperatures increase the material's elastic modulus, increasing the force required for corrugation deformation and thus necessitating greater external force when the hose bends. On the other hand, the contact stress distribution between corrugations may become uneven due to material hardening, and localized stress concentration accelerates fatigue crack initiation. This dual effect is particularly pronounced under frequent bending conditions, potentially shortening the hose's service life.
The impact of low temperatures on metal hose connections is equally significant. Small gaps may form between connectors (such as flanges and fittings) and the hose body due to differences in their thermal expansion coefficients. At low temperatures, these gaps may increase due to contraction, leading to decreased sealing performance or increased leakage risk. Furthermore, stress concentration at connections may be exacerbated at low temperatures, especially when the hose is connected to a rigid pipe. Thermal stress caused by temperature changes may exceed the material's yield strength, triggering localized plastic deformation or cracking.
To address the impact of low temperatures on the flexibility of metal hoses, material selection becomes a crucial strategy. Austenitic stainless steels (such as 304 and 316L) are often used in extremely cold environments due to their excellent low-temperature toughness; nickel-based alloys are suitable for even lower temperature scenarios, such as liquid nitrogen (-196°C) or liquefied natural gas (-162°C) transportation systems. Furthermore, linings or outer layers with non-metallic materials (such as PTFE or rubber) can form composite structures, maintaining the pressure-bearing capacity of the metal hose while using the flexibility of the non-metallic layer to buffer the effects of low temperatures.
Structural design optimization is another important way to improve low-temperature flexibility. Increasing the number of corrugations or reducing the corrugation spacing can improve the bending flexibility of the hose, but pressure resistance must be balanced; using multi-layer corrugated structures or built-in reinforcing layers can enhance the hose's resistance to collapse while maintaining flexibility at low temperatures.
For extreme low-temperature conditions, self-heating hoses can also be designed to maintain the internal temperature through electric heating or fluid circulation, preventing material embrittlement.
In practical applications, the low-temperature performance of metal hoses needs to be rigorously verified through testing. Tests typically include low-temperature bending tests, impact tests, and long-term cycle life tests to evaluate the hose's ability to maintain flexibility at specific temperatures. For example, the 316L stainless steel flexible hoses selected for a liquefied natural gas project passed 100,000 bending cycle tests at -165℃ without cracking or leaking, verifying their low-temperature reliability.
The flexibility changes of metal hoses at low temperatures are the result of the combined effects of material properties, structural design, and environmental conditions. Through reasonable material selection, structural optimization, and rigorous testing, their adaptability in low-temperature environments can be significantly improved, ensuring the safe and stable operation of industrial systems. With the increasing demand for extreme environments such as polar development and deep space exploration, research on the low-temperature performance of metal hoses will continue to deepen, providing theoretical support for technological innovation.
