The Influence Of Corrosive Medium On The Corrosion Fatigue Properties Of Oil Tubing Materials

The working condition of the oil tubing is not only affected by the corrosion damage,but also by the annulus external pressure,internal pressure,bending and vibration load.Corrosion and fatigue can promote the crack initiation and propagation of the oil tubing,until it breaks.The crack initiation life is 10% of the total life,and the crack propagation accounts for 90% in the process of corrosion fatigue.The life is mainly affected by the crack propagation,so it can be forecast oil tube life more accurately by the research of crack propagation rate and characteristics in corrosion environment.In order to ensure the safety of the oil tubing in the oil field development.By changing the concentration and pH of the media,corrosion rate of 13 Cr tubing in different media are obtained.At the same time,this paper makes research on the performance of corrosion fatigue crack growth in the respective medium,and gets fatigue crack propagation curves in corrosion fatigue test.Combined with the effect corrosion rate,the effect of experimental media on corrosion fatigue properties are concluded as follow:(1)The 13 Cr shows better resistant to corrosion,but the corrosion rate will be accelerated with the increase of chloride concentration.The effect of chloride ion concentration on corrosion fatigue crack growth rate is not very high,one reason is the chlorine ion concentration gradient were not big enough,another is the smaller the effect of chloride ion concentration on corrosion fatigue crack growth.(2)13Cr Tubing behaves better resistant to corrosion in the solution with different pH,but corrosion rate increases when pH of solution decreases.In corrosion fatigue,crack propagation rate decreases with the increase of acidity.It is indicated that the corrosion resistance of 13 Cr material does not represent the corrosion resistance.(3)Compared with the atmospheric environment,the fatigue crack growth rate is much faster in corrosive medium.;CO2 could accelerated fatigue crack growth in the later stage of crack propagation;The fatigue crack growth rate of different materials is obviously different in the similar corrosion medium.