Research On The SSC Resistance And Cracking Behavior Of The High Grade Oil Casing And Tubing Steels

In this paper,based on physical and chemical property analysis of high grade oil casing and tubing steels,the stress cracking mechanism of P110?C110 and 125 S three kinds of high grade casing and tubing steels was analyzed by NACE TM 0177-2013 standard A method?four-point bending method and double cantilever beam method;studying the hydrogen permeation behavior and its effect factors of high grade oil casing and tubing steels on the basis of Devanathan-Stachurski electrochemical permeation cell.The results indicated that:compared to P110 steel,the microstructures of C110 and 125 S oil casing and tubing steels were refined and inclusions were spheroidizing,the high density of dislocation and diffuse distribution of carbides were found in the grains;comparing the P110 and 125 S steels,the hardness of C110 oil casing and tubing steel was minimum and impact energy was the highest,C110 steel passed the NACE TM0177-2013 standard for SSC performance testing,having good SSC resistance performance.With the loading pressure and cathode protection potential increases,the SSC sensibility was enhanced;with the temperature increasing,the SSC sensibility was significantly decreased;the KISSC vaule of C110 was larger under high temperature environment and the SSC resistance performance was strengthened.The results of hydrogen permeation behavior indicated that:in the system of 5% wt NaCl solution and NACE TM 0177-2013 standard A solution,the steady-state hydrogen permeation current density and subsurface hydrogen concentration were increased with the H₂ S partial pressure increasing ? the solution pH values reducing and cathode protection potential increasing.The subsurface hydrogen concentration and diffusible hydrogen contents of high grade oil casing and tubing steels increased firstly and then decreased with temperature increasing and extending the corrosion time,the diffusible hydrogen contents in steels was reached the maximum after 168 h?24±3 ??corrosion test.Under the same corrosion environment,the C110 oil casing and tubing steel with typical Cr-Mo composition design has good SSC resistance.The component design of 125 S oil casing and tubing steel was basically same to C110 but it's strength increased,the microstructure was further refined,the number of substructure increases significantly,thus the“hydrogen traping”concentration in 125 S oil casing and tubing steel increases,which results in the increasementof diffusible hydrogen contents and the subsurface hydrogen contents,so the SSC sensitivity was increased.