API
API 5L
Line Pipe
The specification for pipeline steel — grades such as X42 through X70, chemistry, mechanical properties and testing. PSL 1 and PSL 2 differ in how tightly the chemistry and toughness are controlled.
This is an explanation, not the standard. AlpineTutor is not affiliated with API and reproduces no part of the document. Always work to the current edition of the standard itself and to your project specification.