Oil drill pipe is used for oil well drilling. Oil drill pipes are specialized steel pipes used in the process of drilling oil and gas wells. They form a critical part of the drill string, connecting the surface equipment with the drill bit at the bottom of the well. These pipes are designed to withstand extreme conditions, including high pressures, temperatures, and mechanical stresses encountered during drilling.
The production of drill pipe in my country began in the 1990s. The production of drill pipe generally includes three parts: pipe end thickening, tool joint processing, friction welding and subsequent processing.
1. Thickening of pipe ends
The pipe body material of the oil drill pipe is low-carbon alloy steel continuous casting and rolling round steel billet. After being heated in a large rotary furnace, it enters the stretching machine and the mandrel automatic piercing machine for forming. After being heated again, the inner and outer diameters are refined, and straightened before entering the forging process. Since the weld of the oil drill pipe is the weakest link during use, the ends of the seamless pipe must be thickened before welding to increase the thickness to improve the strength of the weak parts and make the overall strength of the weld greater than the overall strength of the pipe body. According to the different pipe diameters, it is generally divided into three types: inside-outside thickening, inside thickening, and outside thickening, among which the inside-outside thickening type is the main one.
The process of pipe end thickening is first to heat and equalize the pipe ends of the seamless pipe; Secondly, the pipe end is pierced by hydraulic or pneumatic means. The outer surface is formed by the mold, and the inner surface is naturally formed by the temperature gradient. Finally, the entire pipe body is heat treated, straightened, and non-destructively inspected. The key technology of pipe end thickening lies in the forming of the inner surface transition zone, because this part is the weakest and most complex in use, and about 70% of accidents occur in this part, so it is of great importance to the quality of the drill pipe.
2. Tool joint processing
The material of the tool joint is generally medium carbon alloy steel. The blank is stamped into shape three times after heating, and then machined after normalizing. First, the inner hole, outer circle and end face of the blank are turned, and then the joint is tempered and heat treated to obtain comprehensive mechanical properties. Finally, the joint is threaded and the threaded part is copper-plated or phosphating to prevent sticking during use.
The quality of the joint depends on two key processes: heat treatment and thread processing. The heat treatment organization directly affects the mechanical properties of the joint, so advanced drill pipe factories use fully automatic continuous controllable atmosphere protection heating and oil or water-based quenching agent quenching. After quenching and tempering, the joints are subjected to surface hardness testing and magnetic particle inspection one by one. After heat treatment, thread processing is carried out. The drill pipe thread is a coarse-pitch tapered thread. In the connection process of the drill pipe, the thread plays a key role. Therefore, thread processing is mostly carried out using high-precision CNC machine tools, and the thread spacing, pitch, taper, tooth height and other parameters of the processed joints are measured one by one to ensure the thread type and accuracy requirements, thereby effectively ensuring the connection performance of the drill pipe joint.
3. Friction butt welding and subsequent processing
Friction welding of drill pipe is an important part of the entire drill pipe production. In order to ensure the welding quality, almost all drill pipe factories use fully automatic friction welding machines and are equipped with welding parameter monitoring devices to automatically monitor and record parameters such as friction time, friction pressure, upsetting pressure, upsetting time and shortening amount during the welding process, thereby ensuring the welding quality. After welding, the welding burrs need to be removed, the heat affected zone needs to be tempered, and the weld needs to be inspected by non-destructive testing. Among them, the tempering heat treatment of the weld is crucial. Almost all manufacturers use medium frequency heating and automatically record parameters such as heating temperature, heating time, holding time, and quenching time. The advantages of this weld heat treatment are: narrow heat affected zone, short heating time, uniform and stable weld zone structure, reliable performance; small residual stress on the weld zone surface.
