Pressure bearing capacity of polyethylene composite pipe reinforced by steel wires after gathering service

In order to clarify the ultimate pressure bearing capacity of polyethylene composite pipe reinforced by steel wires (hereinafter referred to as composite pipe) used for oil gathering in oilfields, a study was performed on 4731B composite pipe tried in No. 4 Oil Production Plant and the anti-scaling composite pipe tried in No. 5 Oil Production Plant of Changqing Oilfield. In the study, 2 groups of transient hydraulic fracturing experiment were performed respectively on the new pipe and the in-service pipe with a 100 MPa burst tester. Meanwhile, the break appearance and burst pressure were analyzed, and the instantaneous strains at different positions during the bursting process were recorded through a strain data acquisition system. The results indicate that the average instantaneous bursting pressure of this composite pipe in service is reduced to some extent, with the break appearance changed dramatically, and the expansion deformation increased significantly in comparison with the new pipes. Besides, the change of strain with time before bursting is divided into 3 stages, i.e., zero strain stage, linear growth stage and exponential growth stage. However, the strain after bursting oscillates until it is stabilized. The reason might be the local failure of adhesive between the steel wire and the high-density polyethylene matrix during the construction of composite pipe. These results could provide reference for the failure analysis of this type of composite pipe applied in oil gathering environment.