API released the APl5L standard in 1926, which initially included only three steel grades: A25, A, and B, with minimum yield values of 172, 207, and 251MPa respectively.
API released the APl5LX standard in 1947, which added three steel grades: X42, X46, and X52, with minimum yield values of 289, 317, and 358MPa respectively.
Since 1966, four steel grades, X56, X60, X65 and X70, have been released, with minimum yield values of 386, 413, 448 and 482MPa respectively.
In 1972, API released U80 and U100 standards, with minimum yield values of 551 and 691Mpa respectively. Later, API changed U80 and U100 to X80 and X100.
Rough statistics show that before 2000, the world's X70 usage was around 40%, and X65 and X60 were both hovering around 30%. A considerable number of small-diameter product oil pipelines also used X52 steel grade, and most of them were ERW steel pipes.
In addition, line pipes transport oil, steam, and water extracted from the ground to oil and natural gas industrial enterprises through line pipes. Line pipes include seamless pipes and welded steel pipes, and their pipe ends have flat ends, threaded ends, and socket ends; The connection methods are welding, coupling connection, socket connection, etc.
