Common steel grades of API 5L steel pipes include A25/L175, A/L210, B/L245, X42/L290, X46/L320, X52/L360, X56/L390, X60/L415, X65/L450, X70/L485, X80/L555, etc. The performance of API 5L steel pipes of different steel grades mainly differs as follows:

Mechanical properties

Yield strength: gradually increases with the increase of steel grade. For example, the yield strength of A25/L175 steel grade is ≥172MPa, while the yield strength of X80/L555 steel grade is 552-690MPa. Steel pipes with high yield strength can withstand greater internal pressure and external loads, are more stable under pressure environments such as oil and gas transportation, and are not prone to deformation.

Tensile strength: also increases with the increase of steel grade. The tensile strength of A25/L175 is ≥310MPa, and the tensile strength of X80/L555 is 621-827MPa. High tensile strength makes it more difficult for steel pipes to be broken when subjected to tensile force. It is suitable for long-distance, large-diameter oil and gas pipelines to resist various tensile forces during pipeline laying and operation.

Elongation: Generally speaking, the elongation of steel pipes with lower steel grades is relatively large, but in general, the elongation of API 5L steel pipes must meet certain standards to ensure that the steel pipes have good toughness and deformation resistance. For example, under the PSL2 standard, the elongation of steel pipes of various steel grades is generally required to be ≥41%.

Impact energy: In the PSL2 standard, for all steel grades except X80, the full-size 0℃ Akv average value is required to be ≥41J in the longitudinal direction and ≥27J in the transverse direction; the X80 steel grade requires ≥101J in the longitudinal direction and ≥68J in the transverse direction. High-grade steel pipes such as X80 have higher requirements for impact energy indicators, which means that they can better resist impact damage and reduce the risk of brittle fracture in harsh environments such as low temperature.

Chemical properties

Carbon content: Under the PSL1 standard, the maximum carbon content of A25 steel grade is 0.21%, and the maximum carbon content of B steel grade and above to X70 steel grade is 0.28%; under the PSL2 standard, the maximum carbon content of B steel grade and above to X80 steel grade is 0.24%. Carbon content affects the strength and toughness of steel pipes. Too high content may reduce the toughness of steel pipes and increase brittleness.

Manganese content: Under the PSL1 and PSL2 standards, as the steel grade changes from A25 to X80, the maximum allowable manganese content gradually increases from 0.60% to 1.40%, and when the carbon content is 0.01% lower than the specified maximum carbon content, the manganese content is allowed to increase by 0.05% compared to the specified maximum manganese content. Manganese can improve the strength and toughness of steel, and an appropriate amount of manganese can improve the comprehensive performance of steel pipes.

Phosphorus and sulfur content: Under the PSL1 standard, the maximum phosphorus and sulfur content is generally required to be 0.030%; the PSL2 standard is more stringent, with a maximum phosphorus content of 0.025% and a maximum sulfur content of 0.015%. Phosphorus and sulfur are harmful elements. The lower the content, the better the corrosion resistance and toughness of the steel pipe.

Processing performance

Welding performance: Low-grade steel pipes such as A25/L175 and B/L245 have relatively good welding performance and relatively low requirements for welding process. High-grade steel pipes such as X70 and X80, due to their high strength and strict control of carbon equivalent, require stricter control of welding process parameters such as welding temperature, speed, preheating and post-heating during welding to ensure welding quality and prevent defects such as welding cracks.

Cold processing performance: Low-grade steel pipes have relatively low hardness. They are easier to form during cold processing such as cold bending and cold drawing, and are not prone to work hardening and cracking. High-grade steel pipes have high strength and are difficult to cold process, requiring greater processing force and more advanced processing equipment. During the processing, care must be taken to prevent performance changes caused by processing stress.