ANSI / API 5L specifies the manufacture of two product levels (PSL1 and PSL2) of seamless and welded steel pipe for the use of a pipeline in the transportation of petroleum and natural gas. For material use in a sour service application, refer to Annex H; for offshore service application, refer to Annex J of API 5L 45th Edition.

In a word, API 5L pipe is the carbon steel pipe applied to the oil and gas transmission system. Meanwhile other fluids like steam, water, slurry also could adopt the API 5L standard for the transmission purposes.