Oil drill pipe is welded from two parts: pipe body and joint. Drill pipe is an important part of oil extraction. It is usually made of 5in (127mm) drill pipe through friction butt welding. Its material is 35CrMo, 40CrMo, 40Mn2Mo or 40CrNiMo steel. During the drilling process, the drill pipe is subjected to various stresses such as tension and compression, bending, torsion and impact. The tension and compression stress is the largest. For example, the tension force of the drill pipe on a 5000m oil well is 12xl04N (without considering the mud buoyancy). Therefore, some drill pipes break near the weld or heat-affected zone due to insufficient strength. On the other hand, drill pipes can also deform and crack due to excessive bending stress. At the same time, fatigue damage of drill pipes is also one of its main failure modes. In drill pipe repair, due to the temperature of about 1300°C during welding and the self-cooling effect of the workpiece, a high-hardness coarse-grained brittle zone is produced in the weld area, which has poor strength and toughness. After welding, heat treatment such as eliminating post-weld residual stress must be performed.
When the drill pipe is running underground, the entire drill pipe is in a flexible state. Due to the high working temperature, it is generally required that the impact absorbed energy in the weld area is >15J to meet the usage requirements. The drill pipe test process uses 35Mn2Mo steel specimens, the heating temperature is 940℃, the cooling rate is 5-14℃/s, a mixed structure of martensite and lath bainite is obtained, and then tempered at (500-600)℃x3min , high strength, plasticity and fracture toughness properties can be obtained, the crack growth rate is significantly reduced, and the working life is extended. The test uses medium frequency induction annealing equipment for quenching + tempering, and the inner and outer walls of the pipe are spray quenched and cooled at the same time. In the test, different cooling rates can be obtained by adjusting the ratio of air and water. The same sensor is used for quenching and tempering, and the size is 190mmx22mm in diameter. To prevent adverse effects in the heat affected zone, the heating zone width should be minimized. Tests show that when the heating temperature is <1000°C, the temperature difference is <25°C, which is acceptable for rapid heating.
The improvement measures for the repair heat treatment process of the drill pipe weld area are as follows:
(1) After the drill pipe is welded, there is considerable internal stress in the weld area. The hardness of this area is high and the structure is coarse and brittle. In order to prevent quenching cracking, a stress relief annealing must be performed after welding. The temperature is preferably 600-650°C. . When the weld is quenched, in order to prevent cracks from occurring, the final cooling temperature should be higher than 10O°C.
(2) Drill pipe repair uses medium-frequency induction heating equipment for quenching and tempering, and the medium-frequency frequency is 1000Hz. The test shows that the medium frequency inductor has reasonable design, excellent spray quenching cooling, uniform hardness distribution and qualified hardness, which meets the technical requirements.
After the repair and heat treatment of the drill pipe weld area, all mechanical properties meet the technical requirements.
This article briefly introduces the improved heat treatment process for the butt welding repair weld area of oil drill pipes. Many manufacturers use the above process to heat treat the butt welding repair weld areas of oil drill pipes. The workpieces produced are of good quality and meet the work needs.
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GS-ZP-1200
