氢气输送管线开裂原因分析

目的对氢气管道内表面开裂原因进行分析,为同类型管道的失效提供参考。方法针对设计压力4.8 MPa、设计温度50℃并在1998年投用的氢气管道,观察其宏观形貌,通过拉伸试验和硬度测试分析其力学性能,并对其进行金相组织分析和扫描电子显微镜观察,通过能谱测试分析其腐蚀产物成分。结果管壁没有明显的腐蚀减薄。管壁整体力学性能符合标准,被测试样韧性较好,未发生材质劣化。基体微观组织为正常的铁素体+珠光体,组织分布均匀,三通及弯管处的焊缝区出现了部分马氏体组织,容易诱发硫化物应力腐蚀开裂的发生。管道内壁存在裂纹及点蚀坑,裂纹扩展较深,且存在分叉,是典型的应力腐蚀特征;点蚀坑有聚集现象,有形成微裂纹的趋势。管道内壁存在腐蚀产物,说明输送的介质不纯净;腐蚀产物中含硫元素,说明介质中含有硫化物等杂质。结论管道操作压力较高,结合其他应力与介质的共同作用,导致管道内壁发生了硫化氢应力腐蚀开裂。

Cause Analysis for Cracking of Hydrogen Gas Pipeline

Objective To investigate the cause for cracking of hydrogen gas pipeline in order to provide reference for failure of the same type of pipes. Methods For hydrogen gas pipeline with a design pressure of 4. 8 MPa and a design temperature of 50 ℃which was put in service in 1998, the macro morphology was observed, the mechanical properties were analyzed through tensile test and hardness test. In addition, optical microscopy analysis and scanning electron microscope ( SEM) observation were conducted, and the composition of corrosion products was analyzed by Energy Dispersive Spectrometer ( EDS) . Results The pipe wall had no obvious corrosion thinning. The overall mechanical properties of the pipe wall conformed to the standard, the tested samples had relatively good toughness and there was no material degradation. The Matrix microstructure was normal ferrite + pearlite, and the structure distribution was even. Some martensite structure occurred in the weld area of T-branch pipe and bending pipe, which was easy to induce the occurrence of sulfide stress corrosion cracking. The internal wall of the pipe had cracks and pitting corrosion, Crack propagation was deep, with split ends, which was a typical characteristic of stress corrosion. The corrosion pits showed gath-ered phenomenon and had the trend of micro cracks formation. The existence of corrosion products on the internal wall of the pipe indicated that the transported medium was not pure. The corrosion products contained sulfur element, showing that the medium contained impurities such as sulfide. Conclusion The relatively high operating pressure of the pipeline, in combination with other joint action of stress and medium, led to hydrogen sulfide stress corrosion cracking of the pipeline internal wall.