Study On Anti-Corrosion Material Selection Of Gathering And Transportation Pipeline Network In An Oil Field

Corrosion has always been the focus of attention in the petroleum industry.Especially in recent years,most oilfields in China have entered the period of high water cut development,and the corrosion of gathering and transportation pipelines has become increasingly serious.Economically and accurately selecting corrosion-resistant metal pipes has become the focus of attention of enterprises.The corrosion environment of oilfield is complex and changeable.Simply relying on laboratory simulation research means is not enough to reflect the real corrosion situation of oilfield,but the research on field corrosion detection is still insufficient.At present,in the field of corrosion resistance of metal materials,there are abundant studies on the effect of alloy composition on corrosion resistance.The effect of different structure regulation(mostly by heat treatment)on the corrosion resistance of materials is still insufficient.Therefore,in view of the specific corrosion environment,the online corrosion test is taken as the research means to analyze the influence of material type and material organization on corrosion resistance.It is not only a theoretical supplement to the field of oil field corrosion research,but also a theoretical guidance for enterprises to select materials scientifically.Taking a typical high water cut oilfield in China as the research background,the specific corrosion environment of A,B and C blocks of the oilfield is studied.Firstly,on-line hanging piece corrosion detection is carried out by means of on-line corrosion detection device,and Corrosion Rules of different materials in corresponding blocks are studied.Secondly,by means of sampling and heat treatment of oilfield steel,and by means of electrochemical performance test,the effect of different structures and corrosion resistance was studied.Finally,the main corrosion factors and corrosion mechanism of the three blocks are identified through the analysis of failed tubing materials in the oilfield,combined with the analysis of liquid-water produced in the blocks and field hanging test data.Secondly,by means of sampling and heat treatment of oilfield steel,and by means of electrochemical performance test,the effect of different structures and corrosion resistance was studied.Finally,the main corrosion factors and corrosion mechanism of the three blocks are identified through the analysis of failed tubing materials in the oilfield,combined with the analysis of liquid-water produced in the blocks and field hanging test data.In addition,optical microscopy,direct reading spectrometer and microhardness tester are used to study the influence of the structure,composition,mechanical properties and corrosion resistance of metal materials.In order to ensure the smooth running of online corrosion detection experiment for hanging pieces,the online corrosion detection device was designed,processed and successfully installed during the research period according to the actual working conditions and experimental requirements of the oilfield.In this research,the experimental results of corrosion resistance of different materials show that: Microstructure analysis showed that low carbon steel A3,20 #,L290 were ferrite + pearlite two-phase structure,ferrite content decreased in turn(from 91% to 63%).In addition,L290 showed obvious banded distribution,which was retained after subsequent heat treatment.In the hardness test,the hardness value of L290 steel with high carbon content and significant pearlite ratio is the highest(317HV).The results of corrosion analysis showed that the corrosion results of hanging pieces were consistent with those of electrochemical tests(JcorrA3 < JcorrL290,Jcorr20 #).The order of corrosion resistance of materials in zone A was A3 > L290 > 20 # steel,and that of materials in zone B was A3 > 20 # > L290.Due to the change of corrosion environment,the corrosion resistance of 20 steel and L290 steel fluctuates.In the area B where corrosion is serious,the corrosion resistance of L290 steel with higher surface hardness exceeds that of 20 steel.The results show that decarbonization of surface structure(decarbonization depth is about 100 um)can greatly reduce the service life of materials under wear and erosion.In the static corrosion environment(3.5% NaCl),surface decarbonization materials have higher charge resistance transfer impedance,and their corrosion properties change,such as 20 steel treated by annealing(holding at 880 C for 30 minutes).The corrosion resistance of A3 material decreases because of the low carbon content and the inhomogeneous structure of retained austenite after heat treatment.The acicular martensite structure was obtained after quenching(water quenching for 5 minutes at 900 C).It has high deposition impedance and is easy to deposit after dissolution.In the study of corrosion mechanism,it is found that NaHCO3 type produced fluid in three blocks A,B and C has high salinity,SRB+CO2 corrosion and Cl-ion catalytic promotion.