Causes Analysis on Cracking of Tubing Coupling in One Well

An investigation on the cracking of tubing coupling resulting in pull out accident of tubing connection was done. The failure analysis was made for cracked coupling and the quality inspection was carried out based on the chemical compositions analysis, mechanical properties test, metallographic examination and fracture analysis. The results show that the tubing coupling cracking was caused by its original defects, and the other tubing tested were in accordance with API standard requirement. Finally in order to use the tubing left in safety and prevent from similar failure accident, some measures were suggested.