Causes of leakage of flexible composite pipe for single well oil and gas gathering and transportation in an oilfield

The flexible composite pipe for single well oil and gas gathering and transportation in an oilfield leaked after 21 months of service.Macroscopic observation,geometric dimension measurement,infrared spectrum analysis,Vicat softening temperature test,hardness test,tensile property test,density test and longitudinal retraction rate test were used to analyze the leakage reasons of the pipeline.The results showed that the operating temperature of the flexible composite pipe was much higher than the design temperature and the Vicat softening temperature of the inner lining layer.During the long-term operation,the oil and gas medium penetrated into the inner lining layer and the reinforcement layer,as a result,the pressure bearing capacity of the pipeline was significantly reduced.Cracks first occurred at the thinnest wall at the bottom of pipeline.Under the action of internal pressure,the pipeline underwent plastic deformation layer by layer,which led to the tearing of the pipeline,resulting in leakage.