Cause Analysis of Round Thread Connection Dropout

Abstract

Dropout may be happen to round thread connection by main reasons of design and process of product, material’s property, make-up torque or make-up position, field operation problems etc.. Casing’s property has get a high improvement with the development over the past decade in China. But the number of connection dropout accident didn’t declined obviously. These lead to great economy loss and safety hazard had taken place. Research on a round thread connection pullout case was carried out combining relative theorys with tests. Macroscopic analysis and dimension measurement and material’s physical and chemical properties were checked for casings and couplings. Thread inspection and full-scale tests were done for casing simples that are same lot with dropout. Comprehensive analysis was carried out on these results. The results showed that dropout failure was ascribe to two main causes. One is make-up location cann’t reach standard location at field end, and the other is incorrect holding position on coupling in the course of making up.