| About one-third of the world's oil and gas fields contain hydrogen sulfide gas.Hydrogen sulfide corrosion is an issue that can not be ignored in the development of sulfur-bearing oil and gas fields.Therefore,anti-sulfur tubes must used in the exploitation of hydrogen sulfide oil and gas field.With the development of deep and ultra-deep wells,oil well pipe service environment is getting worse.Thus it requires that the oil well pipes have a high strength and toughness matching,as well as excellent corrosion resistance.The P110S grade can not meet the requirements,so the development of the Q125S is imperative.Q125S is the highest level of anti-sulfur oil well pipe in the API standard.As the strength increases,the material becomes more and more sensitive to corrosion.It is a great challenge to ensure the high strength of the material and excellent corrosion resistance.Q125S is a high-quality,high value-added products,which has a great market potential at home and abroad.So to carry out Q125 anti-sulfur oil well pipe is of great significance for the domestic steel industry.In this paper,the alloy composition designing,austenitic hot deformation behavior research,microstructure evolution and heat treatment of Q125S oil well pipe and the corrosion property research are conducted.The main results of this paper are as follows:(1)In order to reduce the dislocation density,control the carbide morphology and then enhance the SSC resistance,the content of Cr and Mn in the steel need to be controlled properly.At the same time,it is necessary to add V as well as Nb into the steel.The result of single-pass compression test shows that,the higher the temperature is and the lower the strain rate is,the dynamic recrystallization is more likely to occur.The recrystallization activation energy is 548kJ/mol,and the deformation resistance is predicted to be acccurate in the range of 850?1050? and 0.1?10s-1 by Zhou JH regression model,which is very important to forecast the deformation resistance during hot rolling.(2)The result of dilatormeter is as follows:Ac1 is 756?,Ac3 is 869?,Ar1 is 702?,Ar3 is 830?.The static and dynamic CCT curves of the steels were obtained by the study of austenite continuous cooling transformation rule.The deformation of the steel contributes to the precipitation of the ferrite,resulting in the CCT curve moving to the left and increasing the critical cooling rate of the martensitic transformation.The martensitic is more easily obtained under static condition,and the critical cooling rate of martensitic transformation is 20?/s under static condition.Off-line quenching is recommended to obtain martensite structure.(3)The experimental results show that the parameters of hot rolling and heat treatment in the laboratory are as follows:heating to 1200?,holding for 2h,rolling in two stages,final rolling temperature 880?890?air cooling after rolling;keeping 950? for 40min quenching and tempering for 60min at 710?The mechanical properties of Q125S oil well pipe meet the requirements of API standard.The microstructure is tempering sorbite with lath structure.The two kinds of dislocation substructures inside the slab make the experimental steel have excellent strength and toughness matching.The small dispersed carbides in the ferrite matrix play a role in the hydrogen trap and effectively improve the corrosion resistance of experimental steel.(4)The result of anti-HIC experiment showed that hydrogen bubbling appeared in 1#,3#and 5#samples after immersing in saturated H2S solution(A solution)for 96 hours.According to NACE TM0284-2003 standard,all of them can meet the requirements of hydrogen induced cracking and hydrogen-induced cracking susceptibility is lgreater than 3 greater than 5.Within a certain range,the higher the austenitizing temperature and the tempering temperature are,the better the material's Anti-HIC performance.(5)The results of electrochemical experiments show that when the temperature ranges from 710? to 750?,with the increasing of tempering temperature,there is an extreme value of corrosion rate where the corrosion rate of the experimental steel is the lowest.And the effect of quenching temperature on corrosion rate is relatively small.What's more,the experimental steels all have lower corrosion rate. |
PDF Full Text Request