API is the abbreviation of American Petroleum Institute. Founded in 1919, API is the first national business association in the United States. An important task of API is to be responsible for the standardization of equipment used in the oil and gas industry to ensure the safe and reliable interchangeability of equipment used in the industry. API enjoys a high reputation in the United States and abroad. Its petrochemical and oil production machinery technical standards have been adopted by many countries. It is a petroleum machinery certification body recognized by the US Department of Commerce and the US Trade Commission. API certification standards also enjoy a high reputation internationally. Petroleum machinery with the API mark is not only considered to be reliable in quality but also has advanced technical level, of course, the price is also higher.

API standards are divided into three categories:

(1) Specifications for the design and manufacture of petroleum equipment;

(2) Recommended practices for the use and maintenance of petroleum equipment;

(3) Recommended practices for drilling and production operations.

In general, API standards are reviewed, revised, reconfirmed or withdrawn at least once every 5 years. Sometimes the review period may be extended once, but the extension shall not exceed 2 years. Therefore, the reprint of the air rights has been postponed, and the API standard will no longer be valid after 5 years from the date of publication.

API does not require mandatory laboratory testing for products applying for certification, but for various equipment related to oil and natural gas collection and processing industries, API has proposed 55 detailed specifications. For example, the 6D specification involves pipeline valves, including ball valves, gates, check valves, etc. These specifications set out the minimum requirements that petroleum steel pipe products need to meet. Although there is no mandatory inspection, API observers will check the product plan submitted by the manufacturer to ensure that the manufacturer's production process is in the implementation of the product planning system.

API oil casing is mainly used for the drilling of oil and gas wells and the transportation of oil and gas. It includes oil drilling pipe, steel casing pipe, oil casing, oil extraction pipe.

Oil drill pipe is mainly used to connect drill collars and drill bits and transmit drilling power. The oil casing is mainly used to support the well wall during the drilling process and after the well completion, so as to ensure the drilling process and the normal operation of the entire oil well after the well completion.

Oil casing is the lifeline to keep oil well running. Due to different geological conditions, the downhole stress state is complex, and the combined effects of tension, compression, bending and torsional stress act on the pipe body, which puts forward higher requirements on the quality of the casing itself. Once the casing itself is damaged for some reason, it may lead to a reduction in production of the entire well, or even scrap it.