For tubing coupling failure accidents in recent years, most of the failure analysis showed that the tubing nipple material division standard, the main failure mechanism for tensile overload fracture, this section with a short processing quality, on-site and connection structure has much to do, especially with the tubing hanger connection of double nipple, due to the tubing hanger wall thickness greater than the short section,  As a result, the stress concentration of the tubing sub is caused, and the connection strength is greatly reduced.  

Failure law analysis of tubing joint thread joint under tensile condition.  The law and main reasons affecting the failure of tubing sub are clarified. The main factors affecting the strength of tubing joint and the control indexes of key parameters are determined.  The stress analysis of double male joint is carried out to determine the lifting force during operation.  The structure size of tubing sub was optimized, and the type of sub was simplified from more than 30 types to 5 basic types.  

The field supplementary control method of tubing sub and tubing hanger is studied, and the field application has achieved good effect, effectively reducing the failure of tubing sub and improving the quality management level of tubing sub.  In the study of failure mechanism of tubing sub, it is found for the first time that the eccentricity of outer thread pipe end has a great influence on the joint strength of the sub, which is of great value to optimize the structure of the sub and improve the joint strength.