The alloy design of API pipeline steel is developed based on low C-Mn-Si alloying, which has been maturely applied to API5LB and X42 steel production. APIX52-X70 can be produced by adding less than 0.065% of single microalloying elements or composite microalloying; and adding a small amount of alloying elements (Cu, Ni, Cr) according to the thickness of the steel plate, rolling mill capacity, etc. The main microalloying used in API pipeline steel production is Nb. X52N seamless steel pipe API 5L PSL2 pipeline pipe In order to obtain higher strength, V microalloying is also widely used as an auxiliary role. Without considering the rolling process, the microstructure type of C-Mn-Si micro-alloyed steel is ferrite/pearlite, and the manufacturing cost of this alloying/microstructure design is the lowest.

The alloy design of X70 and above high-grade pipeline steel with higher strength, or the alloy design of X65 steel grade to compensate for the rolling mill capacity, is based on micro-alloyed C-Mn-Si steel while adding a small amount of Cu, Ni, Cr and other elements (either individually or in combination, the total amount should be less than 0.6%), X52N seamless steel pipe API 5L PSL2 pipeline pipe and adding a small amount of Mo (maximum 0.3%) for alloy design. Mo alloying combined with appropriate rolling and cooling processes can obtain ferrite/acicular ferrite structure. In the case of non-Mo alloying, this structure can also be obtained by adding a total amount of up to 0.11% Nb. Because this steel can be produced under higher final rolling temperature conditions, it is called HTP technology.

By increasing the content of Mn, Cu, Ni, Cr, and Mo, and using B micro-alloying technology, X52N seamless steel pipe API 5L PSL2 pipeline pipe APIX100 and APIX120 high-grade pipeline steel can be produced. This alloy design will lead to the appearance of other types of bainite structures and a small amount of martensite, which will reduce the welding performance of steel and increase the manufacturing cost of materials.

Generally speaking, the goal of the ferrite/pearlite structure design is to improve the strength of the X52N seamless steel pipe API 5L PSL2 pipeline. Increasing the alloy composition has a negative impact on the performance of many X52N seamless steel pipe API 5L PSL2 pipelines. Therefore, a good balance must be established between pipelines, structures, and alloying.