tensile strength of welded pipe
When yield of welded pipe increased to a certain extent, because of internal grain rearrange, the ability to resist deformation will increase. Although the deformation develops rapidly, it can only increase the stress until the stress reaches the maximum. Hereafter, the ability to resist deformation of steel is reducing gradually, while plastic deformation occurs at the weakest point. The specimens sectional are narrowing rapidly until the fracture. So the maximum stress of the steel is damaged by pull.
The value (b point corresponds value) is called ultimate strength or tensile strength. Strength and yield limit are determined by experiment. During the tensile test, the stress will reach a certain value though no longer to increase. But the test will continue to grow and the pipes produce significant plastic deformation. If the material loses the ability to resist deformation temporarily, this phenomenon is known as the yield limit of material. When the test tension continues to rise, the specimen reaches the breaking stress, which is called the ultimate or the tensile strength of the material. The yield limit and ultimate strength is much greater, the quality of material is much higher. The strength of the materials is much better to resist destruction and plastic deformation. For certain steel materials, the ultimate strength and yield limit are increased as the operating temperature is reduced.