Acid corrosion is a major problem in the transportation of oil and natural gas. Ordinary seamless pipelines are insufficient in HIC and SSC resistance due to the limitations of chemical composition and production process. The X52 seamless pipeline steel pipe has a sophisticated composition design. The alloy elements V and Al are added to refine the grains, Cu and Ni are added to improve its corrosion resistance and improve the hot brittleness problem, and the content of harmful elements such as S and P is reduced, making it resistant to acid corrosion.
Its main chemical composition and functions are as follows:
C is a carbide-forming element that can increase the strength of steel. To ensure the necessary strength, the lower limit is set at 0.08%, but too high a carbon content will aggravate the formation of banded structure and affect the HIC resistance, so the upper limit is set at 0.16%.
Si is an effective deoxidizing element. Too low a content will lack the deoxidation effect, and too high a content will reduce the toughness of the steel. Therefore, 0.15% to 0.35% is selected as the alloy content range of Si.
Mn is an austenite-forming element, which is used to improve the strength of steel and can make up for the yield strength lost due to the reduction of carbon content. While increasing the strength, Mn can also improve the toughness of steel and reduce the tough-brittle transition temperature. 1.0% to 1.6% is selected as the content range of Mn.
V can prevent the growth of austenite grains and refine the grains. It uses the characteristics of the formed carbides, nitrides, and carbonitrides that dissolve at high temperatures and precipitate at low temperatures to inhibit grain growth and produce precipitation strengthening. Therefore, the V content is controlled at 0.03% to 0.049%.
Al has a great affinity with oxygen and nitrogen in steel. AlN formed by combining with nitrogen can refine the grains, inhibit the aging of low-carbon steel and improve the toughness of steel at low temperatures. The content is controlled at 0.021% to 0.05%.
Cu is an effective anti-HIC element that can accelerate the recombination rate of hydrogen atoms, thereby reducing the activity of hydrogen, improving the corrosion resistance and pitting resistance in acidic media, and enhancing the anti-HIC ability.
Ni has a solid solution strengthening effect, which can promote the formation of stable austenite structure in alloy steel, improve the strength and toughness of steel, and improve the hot brittleness caused by Cu in steel.
P and S are impurity elements, which have a great influence on the anti-HIC performance.
API 5L Grade X52 PSL2 Carbon Steel Seamless Pipes
