API 5CT (American Petroleum Institute Specification 5CT) sets the standards for oil casing and tubing used in the oil and gas industry. The classification of API 5CT oil casing is primarily based on the casing's dimensions, steel grade, and threading specifications. This article will talk about classification of API 5CT oil casing from different aspects.
Nominal Outside Diameter (OD): The casing is classified based on its nominal outside diameter, typically measured in inches. Common sizes include 4.5 inches, 5 inches, 5.5 inches, 6.625 inches, 7 inches, 9.625 inches, and others.
API 5CT specifies different steel grades for oil casing, which are designated by letters (e.g., H40, J55, K55, N80, L80, C90, T95, P110, Q125). Each grade has specific mechanical properties, including yield strength and tensile strength, to meet the requirements of different well conditions.
The casing ends are threaded to facilitate the connection between individual sections of casing. The threading specifications include parameters such as the pitch, crest diameter, and taper. Common thread types include API NUE (Non-Upset End) and API EUE (External Upset End).
Depending on the threading and coupling specifications, API 5CT oil casing can be classified into various connection types, such as short round thread casing (STC), long round thread casing (LTC), and buttress thread casing (BTC). The choice of connection type depends on factors like the well design and the casing string's requirements.
The surface finish of the casing may also be specified, including options such as external bare, external coated, or externally coated and internally coated.
Depending on the well conditions and specific applications, additional requirements may be specified, such as impact testing, non-destructive testing, and special inspection procedures.
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