Tensile strength and Yield strength

Tensile strength and yield strength are two important mechanical properties of metal materials (such as carbon steel pipe). These two indices are closely related to the fatigue-resistant manufacturing and the service life of components.

What is tensile strength?

Tensile strength is an index of mechanical properties of a metal material obtained by a uniaxial tensile test. Tensile strength represents the ability of a metal material to resist deformation and damage under external forces. 

Tensile strength = breaking load / initial cross-sectional area of the specimen.

When the metal has obvious plastic deformation, the cross-sectional area used in the calculation should be the true cross-sectional area measured after the break, and the obtained tensile strength is called the true tensile strength.

This tensile strength index is an index against the maximum deformation ability. In other words, when the deformation reaches this level, the material is broken, and under the condition of uniaxial stretching, no larger deformation can be found. It is a limit and is specific. The tensile sample can withstand the limits of the applied load and is therefore called Ultimate Tensile Strength.

What is yield strength?

Yield strength is a critical mechanical property that marks the point at which a metal material begins to undergo permanent (plastic) deformation. In practice, it is commonly defined as the stress required to produce a 0.2% permanent strain (offset yield strength). Unlike tensile strength, which indicates the maximum stress a material can withstand, yield strength determines the stress level for safe, elastic operation in engineering design.

Yield Ratio:

The ratio of yield strength to tensile strength is known as the yield ratio. A higher yield ratio indicates that the material has a smaller plastic deformation margin after yielding—it will reach its maximum tensile strength and may fracture with less warning. This makes high-yield-ratio materials more prone to sudden failure. Conversely, a lower yield ratio means the material can undergo more plastic deformation after yielding, absorbing more energy before fracture, which is generally considered safer for critical structural applications.

Simply saying that the yield strength is high or the tensile strength is high, then the material is necessarily better or safer. Only steels with high yield strength and low yield ratio are safer.

Read more: 

●  Main Quality Testing Items and Methods of Steel Pipes 

●  ASTM Standard Seamless Pipe Quality Inspection