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API 5CT – Specification for Casing and Tubing 

Spec 5CT specifies the technical delivery conditions for steel pipes (casing, tubing, plain end casing liners, and pup joints) and accessories.

Applicable to the following connections in accordance

（1）short round thread casing (STC);

（2）long round thread casing (LC);
（3）buttress thread casing (BC);
（4）extreme-line casing (XC);
（5）non-upset tubing (NU);
（6）external upset tubing (EU);
（7）integral joint tubing (IJ).

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). The requirements for PSL-1 are the basis of this standard. The requirements that define different levels of standard technical requirements for PSL-2 and PSL-3, for all grades except H-40, L-80 9Cr, and C110, are contained in Annex H. This standard can also be applied to tubulars with connections not covered by API standards,Not applicable to threading requirements.

API 5B-Specification for Threading, Gauging, and Thread Inspection of Casing, Tubing, and Line Pipe Threads

API 5B is the standard specification for threading, gauging, and inspection of Casing, Tubing and line pipe threads.

Spec 5B covers dimensions and marking requirements for API Master thread gauges. Additional product threads and thread gauges, as well as instruments and methods for the inspection of threads for line pipe, round thread casing, buttress casing, and extreme-line casing connections, are included. It is applicable when so stipulated in the API standard governing the product. The inspection procedures for measurements of taper, lead, height, and angle of thread are applicable to threads having 111/2 or less turns per in. (111/2 or less turns per 25.4 mm). All thread dimensions shown without tolerances are related to the basis for connection design and are not subject to measurement to determine acceptance or rejection of product.

Coupling Pipe Grade Identification By Paint Color

Связь colour code
класс	Grade Type	Colour(s) for Coupling		Number andcolour of bandsfor product	Picture
		EntireCoupling	Band(s)
H40		None	Same as for pipe	None/black band at the manufacturer’s option
J55 Tubing		Bright Green	None	One Bright Green
J55 Casing		Bright Green	One White	One Bright Green
K55		Bright Green	None	Two Bright Green
M65		M65Pipe uses L80Type 1Couplings		One Bright GreenOne Blue
N80	1	Red	None	One Red
N80	Q	Red	One Green	One RedOne Bright Green
R95		Brown	None	One Brown
L80	1	Red	One Brown	One RedOne Brown
L80	9Cr	None	Two Yellow	One Red,One Brown,Two Yellow
L80	13Cr	None	One Yellow	One Red,One Brown,One Yellow
C90	1	Purple	None	One Purple
T95	1	Серебряный	None	One Silver
C110		White	Two Brown	One White,Two Brown
P110		White	None	One White
Q125		Orange	None	One Orange