Tubing is the largest industrial product in petroleum industry. It runs through all aspects of oil exploitation, and is the main tool for oil field to develop oil, put the tubing into the production well, and transport the crude oil and natural gas from the bottom of the well to the surface of the ground. The tubing plays an irreplaceable role in the long history of oilfield development. In the process of downhole operation, due to the discontinuity or irregularity of tooth height in the thread manufacturing of some tubing when leaving the factory, the thread sealing surface is damaged when the tubing is screwed on and engaged, resulting in the leakage of production string of oil, gas and water wells, resulting in the rework of operation procedure or the failure of production string, and finally increasing production cost, affecting the oil recovery rate and recovery rate. Therefore, the quality and performance of tubing thread are the important basis to ensure the safety and reliability of oil production well and the production life of oil well.
The common forms of thread defect of tubing are as follows:
1. Local thread tip fillet is discontinuous:
The 55 ° fillet on the top of 8 thread of external thread of tubing is discontinuous. For the thread with 55 ° tooth top, the root of thread appears locally on one side. The tooth top of several threads has only width and no roundness. On the other side, the roundness of the top of the thread is in good condition, that is, the fillet of the local top of the thread is not continuous.
2. The fillet at the top of the circular thread is not continuous:
The top of 8 external thread teeth of tubing is 55 °, the top of several successive threads at the root of upsetting position has only width and no roundness, forming the circular thread tip fillet is not continuous.
The 10 thread also has a tooth top with several consecutive threads at the root with only width and no roundness, forming a circular thread with discontinuous fillet at the tooth top.