L245/316L双金属复合管的失效分析

Failure Analysis of L245/316L Double Metal Composite Pipe

为探明西部某气田L245/316L双金属复合管失效原因,采用一系列理化性能检测方法,并结合现场实际工况,进行综合分析。研究表明:焊接过程中焊趾附近Cr、Ni元素稀释,在Cl-的作用下,形成斜向上的腐蚀凹槽;封焊处存在斜向下的微裂纹,而过渡焊区域为高硬度马氏体组织,裂纹一旦扩展将不具备止裂性能;根焊和过渡焊交界处含有气孔夹杂,气孔周围容易产生应力集中。在以上三个因素共同作用下形成刺漏点,腐蚀性介质通过刺漏点与基管直接接触,基管腐蚀减薄至管壁不能承受内压力而爆管。

In order to find out the cause of the failure of L245/316 Lbimetallic composite pipe in a gas field in west China,a series tests for physical and chemical properties combined with the actual working conditions in the field were carried out to comprehensively study and analysize the failure.The results show that the elements of Cr and Ni were diluted near the weld toe during welding process.Corrosion grooves were formed obliquely upward with the effect of Cl-.Micro cracks obliquely downward at the seal weld were found,and the transition welding area had high hardness with martensitic structure.Once the crack extension happened,the welding would not have the ability to stop cracking.The junction between root welding and transition welding contained pore and inclusion,around which stress concentration was easy to appear.Under the joint action of the above three factors,a leaky point was formed,corrosive medium could directly contact with the basic pipe through the leaky point,and the basic pipe wall was reduced because of corrosion until it could not withstand the internal pressure,and then the pipe ruptured.