Service performances of flexible composite pipe for gas field alcohol injection
Flexible composite pipes with polyester fiber-reinforced nylon inner linings are widely used in high-pressure alcohol-injection environments in gas fields.With an increase of service time,pipeline body aging and joint failures occur more frequently.In order to clarify the performance change and working condition adaptability of this kind of flexible composite pipe after application in a gas field alcohol injection environment,morphology analysis,physical and chemical performances analysis,and pressure bearing performance tests were carried out for each functional layer of the flexible composite pipe before and after service.The results show that the appearance of the nylon inner lining materials and polyester fiber reinforced layer materials of the composite pipe change after service in a high-pressure alcohol-injection environment,and the outer protective layer is cracked.Under the action of methanol,the initial thermal decomposition temperature and melting enthalpy of the nylon inner lining materials are reduced after service of the composite pipe.The methanol medium penetrates into the interlayer of the flexible composite pipe through the inner lining layer,and the polyester fiber undergoes a depolymerization reaction with the alcohol group,resulting in a significant decrease in the tensile properties of the fiber and burst strength of the in-service pipeline.The decrease in the burst strength of the pipe body is in good agreement with the tensile strength of the fiber,and the joint is the weak part.The original PA1212 and PA66 inner lining materials cannot be applied to the field high-pressure alcohol injection conditions for a long time.In the later period,it is recommended to carry out the material selection evaluation for the resistance of the inner lining materials to swelling and permeability of methanol medium before use.
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