The most stressed part of the tubing thread is the root part, so the optimization of the root part is particularly important. In the process of screwing up the round thread of tubing, the force on the two ends of the thread is larger, and the force on the middle part is smaller. In the process of screwing up the round thread of tubing, the stress of the last thread of the partial root of tubing body will exceed the yield limit of N80 steel grade material.
According to the above conclusion, we put forward the following improvement measures to avoid thread sticking of tubing:
After the API tubing round thread machine is tightened, the contact stress at both ends of the engagement thread is large, and the stress in the middle part is small, which is easy to cause the tubing to snap in the use process. Therefore, reduce the contact stress between the tooth surface of the tubing and the coupling thread after engagement, and make the middle part uniform, that is, optimize the thread parameters (such as pitch, tight pitch, etc.), and reduce the peak value of the contact stress on the tooth surface of the thread The important measures to solve the problem of tubing sticking.
According to the stress analysis of each thread, it can be concluded that the stress of the root is the largest. Therefore, the fillet treatment on the bottom of the thread can effectively improve the bearing capacity of the thread of the tubing joint and effectively avoid the problem of sticking.
The sticking is mainly caused by the excessive plastic deformation of the local contact area of the tooth surface, and the performance of different materials is also different, so improving the material performance is also an effective way to improve the anti sticking ability of the tubing thread.
Because API standard is the minimum requirement that manufacturers need to meet, only meeting API standard does not necessarily produce high-quality products that meet the requirements, so it is necessary to match and optimize the thread tolerance within the scope of API standard.