When welded pipe yield to a certain extent, due to the internal grain rearrange and its ability to resist deformation increased, although 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. The maximum stress in the steel by pull before breakage.
Value (b point corresponding value) referred to as the ultimate strength or tensile strength. Strength limit yield limit is determined by experiment. During the tensile test, the stress reaches a certain value, although no longer increase even slightly, the strain of the test piece continues to grow, and produce significant plastic deformation, as if the material temporarily loses the ability to resist deformation, such the phenomenon known as material yield.
Yield stress phenomena occurs, known as the yield limit of the material. When the test tension continues to rise, the specimen reaches the failure stress, known as the ultimate or tensile strength of the strength of the material. Yield limit and the ultimate strength of the greater, respectively, showed that high, that the strength of the material is good material to resist destruction and the ability to resist plastic deformation. For certain materials, the ultimate strength and yield limit is increased as the operating temperature is reduced.
