In the steel pipe standard, according to different application requirements, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness, toughness indicators, and high and low temperature properties required by users are specified. The mechanical properties of large diameter spiral steel pipe are:

Hardness index

The ability of metal materials to resist the indentation of hard objects on the surface is called hardness. According to different test methods and scope of application, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. There are three commonly used pipes: Brinell, Rockwell and Vickers hardness.

Yield point (σs)

For a metal material with a yield phenomenon, the stress at which the sample can continue to elong without increasing the force during the stretching process (maintaining constant) is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).

Upper yield point (σsu): the large stress before the specimen yields and the force drops; Lower yield point (σsl): the small stress in the yield stage when the initial transient effect is not taken into account.

The calculation formula of yield point is:

Where: Fs--yield force (constant) during the tensile process of the sample, N (Newton) So--the original cross-sectional area of the sample, mm2.

Reduction of area (ψ)In the tensile test, the percentage of the large reduction in the cross-sectional area at the reduced diameter of the sample after it is broken to the original cross-sectional area is called the reduction of area. Expressed in ψ, the unit is %. 

Calculated as follows:

In the formula: S0-the original cross-sectional area of the sample, mm2; S1-the small cross-sectional area of the reduced diameter after the sample is broken, mm2.

Elongation after breaking (σ)

In the tensile test, the percentage of the length of the gauge length increased after the sample is broken to the original gauge length is called the elongation. Expressed in σ, the unit is %. 

In the formula: L1-the gauge length of the sample after breaking, mm; L0-the original gauge length of the sample, mm.