API standards are designed to qualify the oil and petrol industry according to the legislation and environment requirements. According to API, oil and natural gas industry can have the reference standards about its industry.Under the general standards, there are some subordinated specifications drafted for each specific OCTG product, such as API 5B, API 5CT, API 5D, API 5L and so on.
API 5L Covers Seamless and Welded Steel Line Pipe.It provide specification for pipe used in conveying gas, water, and oil in both the oil and natural gas industries. It includes standard-weight and extra-strong threaded line pipe; and standard-weight plain-end, regular-weight plain-end, special plain-end, extra-strong plain-end, special plain-end, extra-strong plain-end pipe; as as well as bell and spigot and through-the-flow line(TFL) pipe.
Grades covered by API 5L are A25 ,A ,B (and the following "X" Grades), X42, X46, X52, X56, X60, X65, X70, X80. The two digit number following the "X" indicates the Minimum Yield Strength (in 000's psi) of pipe produced to this grade.
API 5B and 5CT are mainly used for casing and tubing.
API 5B, Specification for Threading, Gauging and Thread Inspection of Casing, Tubing, and Line Pipe Threads.This Specification covers dimensions, tolerances and marking requirements for API threads and the gauges that control the acceptance criteria for the threads. Thread element gauges, instruments and requirements for the inspection of threads for line pipe, round thread casing, and buttress casing connections are included.
API Spec 5CT, Specification for Casing and Tubing, Eighth Edition, Petroleum and natural gas industries-Steel pipes for use as casing or tubing for wells.This Standard specifies the technical delivery conditions for steel pipes (casing, tubing and pup joints), coupling stock, coupling material and accessory material and establishes requirements for three Product Specification Levels (PSL-1, PSL-2, PSL-3).
API 5B and 5CT steel grades are namely H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q-125.Steel grade H, J, K, N in the first group are of relatively low strength. Grade L, C, T represent restricted-yield casing and tubing which are normally anti-sulfur and anti-corrosive. P-110 in the third group is a high strength steel grade.Grade Q-125 is for high strength.
API 5D is under the jurisdiction of the API Committee on Standardization of Tubular Goods.The purpose of this specification is to provide standards for drill pipe suitable for use in drilling and producing operations.API 5D covers Group 1 and Group 3 drill pipe in the designations. API 5D Group 1 - Grade E drill pipe.Group 3 - All high strength grades of drill pipe. (Grades X-95, G-105, and S-135)
API has given each products its special specifications for reference.the main products of OCTG are tubing, casing, drill pipe, drill collar, sucker rod and pipe line. Generally, the standard for tubing and casing is API 5CT standard and API 5D is the standard of drill pipe, while, about line pipe specification,that's API 5L. If you want to process, measure and inspect the screw thread of casing, tubing and pipeline, API 5B is the your choice.