Premature Failures of Rotary-Shouldered Connections RSC Due to Improper

摘要

Premature failures of rotary-shouldered connections (RSC) resulting from improper re-cut and repair operations performed on used connections can cause immense financial loss to oil and gas operators. One of the reasons for improper re-cut and repair procedures is the desire to limit the loss of tool length during thread repair operations. However, this leads to residual damage which can compromise the connection performance and lead to premature connection failures. To study the issue, finite element analysis (FEA) modeling was utilized to determine the distribution of the stresses in RSCs and to map the stress profile at critical locations which could be affected by improper repair operations. In addition, two case studies where the connections of the components failed prematurely in their first run after the connections were freshly re-cut were investigated. The thread repair protocols and post-threading nondestructive inspections were reviewed. Visual examination and optical metallography were utilized to characterize the failure mechanism along with the location of the failures. The failures were not located at the last engaged threads of the connection, which is not typical. Both case studies indicated that the residual damage left from improper thread recut operations had led to the thread failures at non- standard locations. The paper presents the case studies, the details of the metallurgical analysis along with the FEA simulation data. The paper lists the various options available for thread repair along with the commercial benefits associated with these repair options in terms of tool length savings. The paper also presents the failure risks associated with the thread repair techniques. Additionally, the paper discusses the correct re-cut and repair procedures for RSCs along with required NDE inspections that need to be performed after the repair of the connection. By applying and following the recommended repair and inspection protocols, premature connection failures resulting from improper thread repair may be eliminated.