Analysis of the cause of destruction of the repair welded joint of a coiled tubing pipe

Abstract

The article presents the results of studies of the destruction of coiled tubing after repair with the formation of a transverse weld using fusion welding without subsequent heat treatment. The design features of the repair welded joint are considered. A description of the operating conditions of the tubing is presented – ambient temperature, working fluid temperature, pressure, working fluid flow rate, number of round trips, as well as the characteristics of the working environment containing chloride salts, hydrochloric acid solution and gaseous nitrogen (with a high percentage oxygen content). To determine the cause of the failure and identify the corresponding defects, the method of visual-measuring control, determination and analysis of the results of measurements of the hardness and chemical composition of the material of the pipe and weld, mechanical tests were used. Particular attention was paid to fracture analysis, detection of defects in the form of pores, as well as metallographic studies of the microstructure of the welded joint. The ability to use manual arc welding for pipe repair in case of failure, as well as the identification of possible defects obtained during the repair and operation of coiled tubing, allows you to more quickly repair equipment and ensure an increase in its service life, eliminating unwanted downtime. The use of additional heat treatment and well-prepared surfaces for welding by cleaning and degreasing has a significant impact on the quality of the welded joint and leads to minimal formation of defects (pores, microcracks) that affect the further operation of the equipment as a whole, operated under tensile stress conditions during repeated static bending coiled tubing.