Analysis on failure of polyketone lined tubing used in an oil well
[Introduction]Corrosion perforation occurred after 105 days of field application of TP110S tubing lined with POK(polyketone)material in an oil well in Tahe Oilfield.[Method]The failure of tubing substrate was analyzed via morphology observation,chemical composition determination,metallographic structure analysis,hardness test,and tensile test.The physicochemical and thermal properties of POK lining material were evaluated by Vicat softening temperature and oxidation induction time.[Result]The reason for the perforation failure of the lining pipe substrate is that the Cr content of the tubing substrate is low,and it is subject to the synergistic corrosion of CO2 and Cl-in a high temperature environment.The reason for the failure of POK lining is that it undergoes a temperature change from high temperature inside the well to low temperature at the wellhead during the pipe lifting process.At the same time,the lining material is seriously brittle,resulting in partial exfoliation of POK lining during the well lifting process,and the axial tensile stress and flanging preload caused by temperature change lead to obvious retraction of some linings.[Conclusion]In the future,the loading and unloading processes of tubing should be further standardized,the axial stress should be reduced,and the POK material needs to be modified to improve the temperature resistance of linings.