【作者】 王成；

【导师】 徐连勇；

【作者基本信息】 天津大学 ， 材料科学与工程， 2022， 硕士

【摘要】 石油套管服役环境中存在H₂S、CO₂等成分,会加速套管连接处的腐蚀,大大减少其使用寿命,故套管连接处的防腐成为重点关注的问题。利用熔覆工艺在套管接口内壁熔覆耐蚀合金,后在熔覆处开螺纹进行螺纹连接,有望从根本上解决这一问题。为此,本研究选用P110石油套管作为基体材料,利用冷金属过渡加脉冲工艺（Cold Metal Transfer Plus Pulse,CMT+P）在套管接口内壁实现Inconel625合金的熔覆。本文的主要研究内容与结果如下:（1）综合考虑CMP+P熔覆层的熔覆宽度、熔覆厚度、稀释率和润湿角等方面,研究送丝速度、熔覆速度、CMT/P比值以及搭接率等工艺参数对熔覆成型的影响规律。适配的CMP+P熔覆工艺参数:送丝速度8 m/min、熔覆速度8 mm/s、CMT/P比值1:15、搭接率50%、焊丝倾角20°、保护气体流量20 L/min（Ar）、干伸长15 mm。最终成功得到了成型良好,内部无缺陷的P110套管内壁Inconel 625熔覆层。（2）研究了熔覆层的微观组织,发现其组织从底部至表面依次为:柱状晶、树枝晶、等轴晶。熔覆层主要由Ni的固溶体构成,其中分布着一定的Laves相以及MC型碳化物。熔覆层中存在从基体扩散而来的C、Fe元素。（3）对熔覆层不同高度位置试样进行双环电化学动电位再活化腐蚀试验,其结果均为轻微敏化（距离熔合线2.5 mm处对应敏化指数为1.4%、1.5 mm处为2.9%、0.5 mm处为4.2%）。熔覆层耐晶间腐蚀性能受到从基体中扩散过来的C、Fe元素含量及晶界特征的影响,随着熔覆层中C、Fe含量减少（C含量依次为0.043%、0.038%、0.036%,Fe含量依次为3.30%、2.65%、2.81%）、小角度晶界和Σ3ⁿ晶界增加（小角度晶界含量依次为14.8%、15.6%、16.2%、Σ3ⁿ晶界含量依次为5.4%、11.7%、21.3%）,其抗晶间腐蚀的能力均有所提高。（4）熔覆层在H₂S/CO₂浸泡腐蚀中腐蚀速率为0.01 mm/y,具有良好的耐腐蚀性能。腐蚀后,试样表面存在一层Cr₂O₃薄膜,其上分布着一些微小的富硫富钼类化合物。更多还原

【Abstract】 Due to the presence of H₂S,CO₂ and other components in the service environment of the oil casing,which will accelerate the corrosion of the casing joint and Creatly reduce its service life.Therefore the corrosion resistance of the oil casing connection has become a key concern.It was expected to fundamentally solve this problem by using the cladding process to clad the corrosion-resistant alloy on the inner wall of the casing interface,and then set the thread at the cladding for threaded connection.Thus,this study selects P110 steel Crade oil casing as the base material,Inconel 625 alloy as the cladding material,and uses the Cold Metal Transfer Plus Pulse（CMT+P）process to achieve cladding on the inner wall of the oil casing interface.The main research contents and results of this paper were as follows:（1）Considering the cladding width,cladding thickness,dilution rate and wetting angle of the CMP+P cladding layer,the process parameters such as wire feeding speed,cladding speed,CMT/P ratio and lap ratio on cladding forming were studied.Adapted CMP+P cladding process parameters:wire feeding speed 8 m/min,cladding speed 8 mm/s,CMT/P ratio 1:15,overlap ratio 50%,and wire inclination angle 20°,The protective gas flow rate 20 L/min（Ar）,the dry elongation 15 mm.The Inconel625 cladding layer on the inner wall of the P110 casing with good molding and no internal defects is successfully obtained.（2）The microstructure of the cladding layer was studied,and it was found that the structure from the bottom to the deposition was:columnar crystal,dendrite,and equiaxed crystal.The cladding layer was mainly composed of a solid solution of Ni,in which a certain Laves phase and MC-type carbides are distributed.There were C and Fe elements diffused from the matrix in the cladding layer.（3）The Double loop electrochemical potentiokinetic reactivation was carried out on the samples at different heights of the deposited layer,and the cladding layer was slightly sensitized during the test（The corresponding sensitization index was 1.4%at2.5 mm from the fusion line,2.9%at 1.5 mm,and 4.2%at 0.5 mm）.The intergranular corrosion resistance of the cladding layer is affected by the content of C and Fe elements diffused from the matrix and the characteristics of Crain boundaries.Specifically,with the decrease of C and Fe contents（The C content was 0.043%,0.038%,0.036%,and the Fe content was 3.30%,2.65%,2.81%）,the increase of low-angle Crain boundaries andΣ3ⁿ Crain boundaries（The content of low-angle Crain boundary was 14.8%,15.6%,16.2%,and the content ofΣ3ⁿ Crain boundary was 5.4%,11.7%,21.3%）,the resistance to intergranular corrosion is improved.（4）The corrosion rate of the cladding layer in H₂S/CO₂ immersion corrosion test was 0.01 mm/y.The cladding layer has good corrosion resistance.After corrosion,there was a layer of Cr₂O₃ film on the surface of the sample,on which some tiny sulfur-rich and molybdenum-rich compounds were distributed.更多还原