Property Analysis on High Strength Pipeline Steels

Both imported coils and domestic steel coils have been used in Korla-Shanshan crude oil pipeline. As for the variation of yield strength during the process of making pipes, small specimen was used in the test to accurately demonstrate the effect of Bauschinger Effect. Having made the analysis of testing and comparison of properties and technologies between two kinds of steel, the different distribution of hardness has been found. As to imported steel, hardness is almost consistent between center and surface, as to domestic steel, the hardness is highest in the center. And the hardness is getting lower and lower at the range from point of 1.5mm away from the center to the surface, hardness in surface is the lowest. The reason of the result should be related with the process of producing of steel coil. Process of metallurgic condensing makes the content of carbon and alloy in the surface lower than it in the center, and process of rolling makes the hardness in the surface of steel higher than it in the center. The properties of the imported coils show the result of combination of two factors above mentioned.