双金属复合管焊接接头组织与性能研究

发布时间：2018-06-27 23:17

本文选题：双金属复合管 + 焊接接头　；参考：《西南石油大学》2017年硕士论文

【摘要】：双金属复合管由于其突出的性价比,目前在油气田建设及运输方面应用得越来越广泛。但是复合管基层与覆层的化学成分以及物理性能差异较大,在进行管道的焊接连接时,过渡层焊缝属于异种金属的焊接,相比于同种金属来说难度更大。尤其是机械式复合管,其基层和覆层之间存在一定缝隙,里面可能含有空气、水分及其他夹杂物,在进行过渡层的焊接时容易导致层间出现气孔、熔池塌陷形成焊瘤以及焊不透等一系列焊接缺陷。因此,本文针对机械式双金属复合管焊接问题,制定了三种不同的焊接方案,分别采用了 V型坡口、封焊坡口和堆焊坡口对X65/316L双金属复合管进行焊接,对获得的焊接接头分别进行了组织与成分分析、力学性能测试与腐蚀性能测试,根据试验结果评价三种焊接接头性能的好坏,从而判定三种焊接方案的设计是否合理。显微组织观察结果表明:三种焊接方案下的复合管焊接接头焊缝组织均为铁素体+奥氏体双相组织,并且在Ni、Cr等元素含量高的地方出现了以胞状晶、树枝晶和等轴晶等不同方式生长的晶粒形态。过渡层焊缝物相分析表明:三种复合管焊接接头过渡层焊缝的物相均由α+γ两相组成,没有发现σ相、M23C6相等有害相析出。熔合区元素线扫描分析表明:Ni、Cr、Mo等合金元素在该区域均产生了一定的浓度梯度,但是并未发生明显的偏聚现象,C元素在V型坡口焊接接头和封焊坡口焊接接头中出现了轻微的扩散迁移现象。力学性能测试结果表明:V型坡口焊接接头、封焊坡口焊接接头和堆焊坡口焊接接头的显微硬度最大值分别为231HV、213HV、222HV,均小于酸性介质下管线钢的硬度极限值250HV,说明硬度方面三种焊接接头均合格,其中焊缝区域的显微硬度值均比热影响区和母材区域要高。三种焊接接头的屈服强度平均值分别为443.7MPa、462.3MPa、481.7MPa,其中V型坡口焊接接头没有达到复合管基层X65母材的最低屈服强度值448MPa,而另外两种焊接接头满足要求。三种焊接接头的平均冲击韧度均达到X65碳钢母材的使用要求,焊缝区域的冲击韧度普遍比热影响区的冲击韧度要高。三种焊接接头焊缝和热影响区的冲击断口表现为大小和深度不等的等轴韧窝形貌,并且都伴有山脊状撕裂棱存在,属于典型的韧性断裂机制。腐蚀性能测试结果表明:电化学测试结果和化学浸泡试验结果比较一致,都表明了三种复合管焊接接头具有较好的耐腐蚀性能,其中封焊坡口焊接接头和堆焊坡口焊接接头的耐腐蚀性能优于316L不锈钢母材,而V型坡口焊接接头的耐腐蚀性能比316L母材要差。综上所述,采用V型坡口进行复合管焊接的试验方案不能满足实际工程需要,而采用封焊坡口和堆焊坡口的焊接方案参数设计比较合理,满足实际生产要求。
[Abstract]:Bimetallic composite pipe is widely used in oil and gas field construction and transportation due to its outstanding cost-performance ratio. However, the chemical composition and physical properties of the base layer and the cladding of composite pipe are quite different, so the welding seam of transition layer belongs to dissimilar metal, which is more difficult than that of the same metal. In particular, there is a gap between the base layer and the cladding of a mechanical composite pipe, which may contain air, moisture and other inclusions, which can easily lead to blooms between layers when welding the transition layer. Weld pool collapse forms a series of welding defects, such as welding nodule and welding failure. Therefore, in order to solve the welding problem of mechanical bimetallic composite pipe, three different welding schemes have been developed in this paper. The V groove, sealing groove and surfacing groove are used to weld X65p 316L bimetal composite pipe, respectively. The microstructure and composition of the welded joints were analyzed, the mechanical properties and corrosion properties of the welded joints were tested, and the performances of the three welded joints were evaluated according to the test results, so as to determine whether the design of the three welding schemes was reasonable or not. The results of microstructure observation show that the weld microstructure of welded joint of composite pipe under three kinds of welding schemes is ferrite austenitic dual phase structure, and the cellular crystal appears in the place where the content of nio Cr and other elements is high. Dendritic and equiaxed crystal growth in different ways of grain morphology. The phase analysis of transition layer weld shows that the phase of transition layer weld of three kinds of composite pipe welded joint is composed of 伪纬 two-phase, and no 蟽 phase M23C6 is found to precipitate from the same harmful phase. The linear scanning analysis of the elements in the fusion region shows that there exists a certain concentration gradient in the fusion region. However, there is no obvious segregation phenomenon of C element in V-groove welded joint and seal weld groove welding joint, there is a slight diffusion migration phenomenon. The test results of mechanical properties show that: v groove welded joint, The maximum microhardness of seal welded groove joint and surfacing groove welding joint is 231HVP213HV222HVrespectively, which is less than the hardness limit value of pipeline steel in acid medium 250HV. it shows that the hardness of the three welded joints is up to standard. The microhardness of weld zone is higher than that of heat affected zone and base metal zone. The average yield strength of the three welded joints is 443.7 MPA / 462.3MPA / 481.7 MPa respectively. The V groove welded joint does not reach the minimum yield strength value of the base material X65 of the composite pipe, while the other two kinds of welded joints meet the requirements. The average impact toughness of the three welded joints is up to the requirements of the base metal of X65 carbon steel, and the impact toughness of the weld zone is generally higher than that of the heat-affected zone. The impact fracture of the weld and heat affected zone of the three kinds of welded joints shows the shape of equiaxed dimples with different sizes and depths, and all of them are accompanied by ridge-like tearing edges, which is a typical ductile fracture mechanism. The results of corrosion test show that the results of electrochemical test are consistent with those of chemical immersion test. The results show that the three kinds of welded joints of composite pipe have good corrosion resistance. The corrosion resistance of sealing and surfacing groove welded joints is better than that of 316L stainless steel base metal, but the corrosion resistance of V-groove welded joints is worse than that of 316L base metal. To sum up, the test scheme of using V-shaped groove to weld composite pipe can not meet the actual engineering needs, but the welding scheme parameters of sealing welding groove and surfacing groove are more reasonable and meet the actual production requirements.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407

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