Line pipe is manufactured from high-strength carbon steel, and is made to strict engineering and metallurgical specifications developed by the American Petroleum Institute (API). One particular standard, API Specification 5L, defines requirements for pipe made to transport natural gas, oil and water. This specification includes standards for the dimensional, physical, mechanical, and chemical properties of the carbon steel. Several pipe mills around the world manufacture API 5L line pipe for the natural gas industry. http://www.sellsteels.com/steel-pipe/API-5L.