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When steel pipe yield is to a certain extent, due to the internal grain rearrange its ability to resist deformation increased, although at this time deformation developed rapidly, but it can only be increased as the stress increased, until the stress reaches the maximum value. Thereafter, the ability of steel to resist deformation is significantly reduced, and the large plastic deformation occurs at the weakest point, here specimens sectional rapidly narrow, the phenomenon of necking until fracture. Steel by the pull before breakage of the maximum stress value is referred to as the ultimate strength or what is the tensile strength.

Specimen during the tensile pull off withstand most strongly (Fb), the resultant stress (蟽) divided by the sample of the original cross-sectional area (So), referred to as the tensile strength (蟽b), in units of N/mm2 (MPa). It indicates the maximum capacity of the metal material under tension resistance to damage. Calculated as follows: where: Fb - the sample pull off when bear most vigorously, N (Newton); So - the original specimen cross-sectional area, mm2.