Analysis of the Failure Causes of High Strength Corrosion Resistant Oil Casing to SSC
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 H2S,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.
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