NDT Testing

The pipeline is not only affected by the pressure and temperature of the transmission medium, but also by various natural and human factors, which may occur in the process of leakage or damage of various accidents. Not only because the pipeline leakage accident affects the transportation, causes the economic loss, but also pollutes the environment. In order to ensure the safe operation of the pipeline and the prevention of pipeline accidents, it is very important to design, construct and operate the pipeline, including the design and reasonable selection of the pipeline. For pipes, strength, toughness and weldability are three basic quality standards. The corrosion of environment and transportation medium to the pipeline shall also be considered, and the corrosion-resistant steel shall be selected.


(1) Mechanical properties: the main indicators to measure the mechanical properties of pipes are strength, yield limit, elongation, etc.

① Tensile strength: in the tensile test, the stress corresponding to the maximum drawing of the sample.

② Yield strength: in tensile test, the minimum stress of the specimen in service when the initial buckling effect is not included.

③ Elongation: a measurement of set steel, which refers to the elongation after drawing out the sample in the tensile test, and the elongation at the original distance from the standard gauge.


④ Bauschinger effect: metal or alloy produces micro plastic deformation after preloading, and then increases with the increase of elastic limit load, while reverse load reduces the incompleteness of elastic limit.


(2) Fracture toughness: pipeline fracture can be divided into fracture toughness and brittle fracture toughness.




① Ductile fracture: under the condition of over tensile stress, the gradual expansion and final fracture caused by tiny crack, and the crack exists at the same time.



② Brittle fracture: it is caused by the combination of temperature, stress and crack. Under sudden conditions, the fracture is often much lower than the early yield stress.


③ Fracture toughness: energy and the ability to attribute the deformation of a metallic material to cracks before failure absorption.


④ Ductile brittle transition temperature: within a certain temperature range, fracture toughness can only be obtained at a lower temperature.


Reduce. When the temperature is close to the front temperature of the main road, there will be a sudden drop in toughness, which makes the steel change from brittle fracture to brittle fracture. This temperature is called the ductile brittle transition temperature of steel.