What are the key differences between PSL1 and PSL2 in API 5L X52?

The main differences between PSL1 and PSL2 in API 5L X52 are as follows:
Different chemical composition requirements
Carbon content and carbon equivalent: PSL2 usually has stricter restrictions on carbon content and carbon equivalent. For example, for seamless steel pipes, the maximum carbon grade AB of PSL1 is 0.28%, while PSL2 is 0.24%; for welded pipes, the maximum carbon content AB grade of PSL1 is 0.26%, and PSL2 is 0.22%. This makes PSL2 grade steel pipes more advantageous in terms of strength and weldability.
Impurity element content: PSL2 has stricter restrictions on harmful impurity elements such as phosphorus and sulfur. The maximum content of phosphorus in PSL1 is generally 0.030%, while PSL2 is 0.025%; the maximum content of sulfur in PSL1 is 0.030%, and PSL2 is 0.015%. Lower impurity content helps improve the corrosion resistance and toughness of steel pipes.
Different mechanical property requirements
Impact performance: PSL1 does not require impact performance testing, while for all steel grades except X80, the average value of Akv at 0℃ in the full size is ≥41J in the longitudinal direction and ≥27J in the transverse direction; for X80 steel grade, the average value of Akv at 0℃ in the full size is ≥101J in the longitudinal direction and ≥68J in the transverse direction. This means that PSL2 grade steel pipes are more resistant to impact and have better toughness under harsh conditions such as low temperature.
Yield strength and tensile strength: PSL2 has clear maximum limits for the yield strength and tensile strength of each steel grade, while PSL1 usually does not have such strict requirements, which makes the strength performance of PSL2 steel pipes more guaranteed and can better withstand the pressure during pipeline operation.
Different manufacturing process requirements
Welding process: PSL2 has more stringent requirements on welding process. For example, when welding, PSL2 stipulates that the minimum welding machine frequency is 100kHz, while PSL1 has no such minimum value limit.
Heat treatment of welds: In PSL1, only welds of steel grade X42 are required to undergo heat treatment, while welds of all steel grades in PSL2 are required to undergo heat treatment, which helps eliminate welding stress and improve weld quality and the overall performance of steel pipes.
Different inspection and testing requirements
Nondestructive testing: PSL1 does not require nondestructive testing, while PSL2 should undergo nondestructive testing for each pipe. For example, ultrasonic testing, radiographic testing and other methods can be used to more comprehensively detect defects inside and on the surface of steel pipes to ensure the quality of steel pipes.
Pipe end treatment: The pipe ends of PSL2 usually must be sandblasted, while PSL1 generally does not have this requirement. Sandblasting can clean the surface of the pipe ends and improve the performance of subsequent processing and use.