The basic situation of API standard tubing and casing thread connection:
The API standard threaded connection of tubing and casing
in petroleum special pipes consists of two parts: pipe or male end and coupling or female end. Those with external threads are called pipes or male ends, and those with internal threads are called couplings or female ends.
The two male ends are connected by a coupling, which is a short tube with an outer diameter slightly larger than that of the pipe. Both ends have internal threads. All casing and line pipes with API threads and couplings are not thickened.
The tubing is not thickened or thickened on the outside. The inner diameter of the pipe end is approximately equal to the inner diameter of the pipe body, but the outer diameter of the thickened end is larger than that of the pipe body, and the two ends of the integral connecting tubing are thickened.
The API specification includes 4 kinds of threads, namely, line pipe thread, round thread, buttress thread and direct connection type thread. Line pipes, round threads, and trapezoidal threads are required to be matched together during screwing and assembly to prevent leakage from the threads with sealing filler grease. The thread end of the direct connection type casing is designed to be sealed, and the sealing of the direct connection type connection is realized by a metal-to-metal seal.
The main parameters of API standard threads include:
(1) Thread length, (except for trapezoidal thread): the length from the starting point (pipe end) of the thread to the vanishing point;
(2) Thread height: the distance between the top of the thread and the bottom of the tooth;
(3) Pitch: the distance from any point of the thread to the corresponding point of the adjacent tooth in the axial direction;
(4) Thread taper: the change in thread diameter per inch of thread length expressed in inches;
(5) Close distance: the distance measured in the axial direction from the end face of the pipe or coupling to the tightening position of the ring gauge or plug gauge;
(6) Thread tail taper (only partial ladder thread): The rapid retreat of the cutting tool causes a steep slope at the end of the thread.