气田注醇用柔性复合管服役性能

Service performances of flexible composite pipe for gas field alcohol injection

采用涤纶纤维增强尼龙内衬的柔性复合管在气田高压注醇环境中得到大量应用,随着服役时间的增加,管线本体老化和接头失效频发。为明确该类柔性复合管在气田注醇环境应用后性能变化及其工况适应性,针对服役前后柔性复合管各功能层,开展了形貌分析、理化性能分析及承压性能测试。结果表明,在高压注醇环境服役后复合管尼龙内衬层材料和涤纶纤维增强层材料外观发生了一定变化,外保护层龟裂。在甲醇介质作用下服役后的复合管尼龙内衬层材料初始热分解温度和熔融焓降低。甲醇介质经内衬层渗透进入柔性复合管夹层,聚酯纤维与醇类基团发生解聚反应,致使复合管服役后的纤维拉伸性能及在役管线爆破强度显著降低。管体爆破强度降低情况与纤维拉伸性能具有较好的一致性,且接头为薄弱部位。原有PA1212和PA66内衬材料不能长期适用于现场高压注醇工况环境,后期建议使用前针对内衬材料开展耐甲醇介质溶胀及渗透性能选材评价。

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.