Introduction to the tensile strength of steel pipes
Date:2025-07-24
As the basic structural material in modern engineering, the tensile strength of steel pipes is a key mechanical performance index to measure their ability to resist axial tensile fracture, which directly affects the safety, reliability and service life of the structure.
1. The core definition of tensile strength
Concept: It refers to the maximum engineering stress that a steel pipe can withstand from the beginning of deformation to the final fracture under the action of axial tensile load. It represents the ultimate ability of the material to resist tensile damage.
Unit: Usually expressed in megapascals (MPa) or pounds per square inch (psi).
Key point: Tensile strength (Rm or TS) is the limit of material failure. Once the working stress exceeds this value, the steel pipe will break.
2. The main factors determining the tensile strength of steel pipes
Basic material: This is the most fundamental determining factor.
Carbon steel: The most widely used, such as Q235, Q345 (GB standard), ASTM A53, A500, etc. Its strength increases with the increase of carbon content, but the toughness may decrease.
Alloy steel: By adding elements such as manganese (Mn), chromium (Cr), molybdenum (Mo), vanadium (V), and nickel (Ni), the strength, toughness, and corrosion resistance are significantly improved. Such as ASTM A335 P11/P22/P91 used for high-pressure pipelines.
Stainless steel: Chromium and nickel are the main alloying elements (such as 304, 316, and duplex steel 2205). In addition to excellent corrosion resistance, its tensile strength is usually higher than that of ordinary carbon steel (such as the tensile strength of 304 stainless steel ≥515 MPa).
Manufacturing process and status:
Hot rolling: Rolling above the recrystallization temperature, high production efficiency and low cost. The strength is usually lower than cold rolling, but the toughness is better.
Cold rolling/cold drawing: Plastic deformation processing at room temperature. This process causes significant work hardening, which can greatly improve the tensile strength and hardness of the steel pipe, but the plasticity and toughness will be reduced. The finished product has higher dimensional accuracy.
Heat treatment: Such as normalizing, annealing, quenching + tempering (quenching and tempering), etc., can optimize the microstructure of the material and achieve the best balance between strength, plasticity and toughness. For example, quenching and tempering is a common means to obtain high strength and toughness.
Welding: The strength properties of welded steel pipes are significantly affected by the parent material, welding materials and welding processes (such as submerged arc welding SAW, high frequency welding HFW, electric welding ERW). The weld area may have softening of the heat-affected zone or uneven structure, and its strength needs to be assessed separately (usually the weld strength is required to be no less than the parent material).
Geometric dimensions:
Although tensile strength itself is a material property (force per unit area), it is theoretically unrelated to absolute dimensions such as steel pipe wall thickness and diameter. However, it should be noted that:
Test representativeness: There may be performance differences between the surface and core of thick-walled pipes (such as different cooling rates).
Structural behavior: In actual structures, the size of the steel pipe (wall thickness, diameter) directly affects its bearing capacity (total tensile force that can be sustained = tensile strength × cross-sectional area of the steel pipe). The thicker the wall and the larger the diameter, the greater the total tensile force it can withstand.
