高强耐蚀油套管抗SSC失效原因分析

Analysis of the Failure Causes of High Strength Corrosion Resistant Oil Casing to SSC

对抗SSC失效的C110级油套管进行断口形貌观察,通过对比失效钢管和正常钢管的化学成分、力学性能、金相组织和晶体学特征等,分析C110级油套管抗SSC异常失效的原因。结果表明,失效钢管断口裂纹源处未发现大颗粒非金属夹杂或气孔的冶金缺陷,失效钢管相对于正常钢管,其基体组织低角度晶界比例和位错相对更多,受亚晶界和位错等缺陷处捕氢能力较强的影响,在富含H_(2)S的环境下,晶体缺陷部位局部氢含量富集,导致氢致开裂。为进一步分析晶体缺陷的产生原因,反溯了失效钢管的生产工艺,该批钢管在入库检测时发现出现了尺寸偏差,后续经冷拔处理,变形部位在冷拔过程中聚集了大量的位错和低角度晶界,导致钢管抗SSC失效。

The fracture morphology of C110 grade oil casing against SSC failure was observed.By comparing the chemical composition,mechanical properties,metallographic structure,and crystallographic characteristics of the failed steel pipe and normal steel pipe,the reasons for the abnormal failure of C110 grade oil casing against SSC were analyzed.The results showed that no metallurgical defects such as large non-metallic inclusions or pores were found at the crack source of the fracture surface of the failed steel pipe.Compared with normal steel pipes,the proportion of low angle grain boundaries and dislocations in the matrix structure of the failed steel pipe was relatively higher.Due to the strong hydrogen capture ability of defects such as subgrain boundaries and dislocations,the hydrogen content was enriched locally at the crystal defect site in an environment rich in H_(2)S,leading to hydrogen induced cracking.To further analyze the causes of crystal defects,the production process of the failed steel pipes was traced back.During the incoming inspection,it was found that there was a size deviation in this batch of steel pipes.After cold drawing treatment,a large number of dislocations and low angle grain boundaries accumulated in the deformed parts during the cold drawing process,resulting in the failure of the steel pipes'resistance to SSC.