Failure Analysis on Cracking of P110 Grade Tubing Couplings

Large quantities of cracking happened to P110 grade tubing couplings fractured inside within a short time after being applied in a well for oil test operation.The cracking reasons were analyzed by means of macro and micro analysis,chemical compositions analysis,mechanical properties test,metallographic examination and corrosion products analysis.The results show that the cracking initiated from the exterior surface of the coupling where the axial tensile stress was the largest,and under the action of nitrate inside the well casing stress corrosion cracking happened.