Pipeline bears the influence of pressure and temperature of pipeline medium, but it is also affected by various transportation through the heart, natural and human factors that may occur in the process of leakage or destruction of various accidents. It not only causes economic losses due to pipeline accident leakage, but also pollutes the environment. In order to ensure the safe operation of pipelines and prevent pipeline accidents, it is very important to design, construct and operate pipelines, including the design and reasonable selection of pipelines. As for pipes, strength, toughness and weldability are three basic quality standards. It should also consider the environmental and transport media pipeline corrosion, corrosion-resistant steel selection.


(1) Mechanical properties: The main indexes for measuring the mechanical properties of pipes are strength, yield limit, elongation and so on.
Tensile strength: In the tensile test, when the specimen corresponds to the maximum drawing stress.
(2) Yield strength: In the tensile test of steel, the specimen is deformed in tension. When the initial transient buckling effect is excluded, the minimum stress in the service stage is obtained.
(3) Elongation: A measure of forming steel refers to the elongation of the steel in the original distance of the standard gauge and the sample taken out in the tensile test.
(4) Bauschinger effect: After unloading, metals or alloys produce micro-plastic deformation under preloading, and then with the increase of elastic limit of load, reverse load reduces the phenomenon of incomplete elastic limit.


(2) Fracture toughness: Pipeline rupture can be divided into fracture and brittle fracture toughness.
(1) Ductile fracture: gradual expansion and ultimate rupture caused by micro-cracks existing at the same time as excessive tensile stress.
(2) Brittle fracture: The temperature, stress and crack caused by the combined action of three conditions are often much lower than the yield stress under sudden conditions.
(3) Fracture toughness: energy and the ability to attribute the deformation of metal materials to cracks before they are destroyed and absorbed.
(4) Ductile-brittle transition temperature: Within a certain temperature range, fracture toughness only needs to use a lower temperature.
Lower. When the temperature is close to the front temperature of the main road, the toughness will drop suddenly. The steel will change from crushing to brittle fracture toughness. This temperature is called the ductile-brittle transition temperature of steel.