Study On The Residual Strength Of Casing And Tubing With Corrosion Damage

The corrosion damage of casing and tubing is one of the important problems in the development of oil and gas field,and it is also the main form of casing and tubing damage.After the casing and tubing is corroded,the residual strength of casing and tubing is reduced,which leads to the leakage of casing and tubing perforation and so on.In this paper,the residual strength of casing and tubing with corrosion damage is studied,which is of great significance and practical value to improve casing strength,rationally optimize casing and tubing material and prolong oil and gas well production life in casing and tubing design.The mechanical properties of the casing and tubing after corrosion were tested by small punch experiment,and the formula for solving the yield strength and tensile strength was studied.The relationship between pm/t2,Pm/t 和 Pm/(dm*t)and tensile strength is analyzed by linear fitting.And get the most suitable for the analysis of tensile strength formula:σb=αpm/dm·t.By lincar fitting,the relationship between Py Mao/t2,Py_CEN/t2,Py t/10/t2,Py-t/10/t2 and yield strength is analyzed,and the most suitable formula for analyzing tensile strength is obtained:σy=βPy t/10/t2.The results show that the yield strength and tensile strength of three different types of Casing and tubing steels have less change after corrosion.Using the modified material parameters,the residual strength of the common material N80 steel casing is simulated.The study of residual strength of casing and tubing with single pit shows that the stress concentration of groove corrosion defects is serious in circumferential direction and the stress concentration in axial direction of casing and tubing is serious,and it is easy to fail in the direction of severe stress concentration.The depth of defect is the most important factor affecting the residual strength of Casing and tubing,The width of groove corrosion defect and the radius of pitting opening are not the main factors.For groove corrosion defects,the residual strength of casing and tubing is p=(32.61-1.50a)-3.75 Ln(c-5.68),and the residual strength of casing and tubing with pitting corrosion is decreased with the increase of defect depth,while that of corrosion pits with same depth and groove corrosion defects have greater influence on residual strength of casing and tubing than pitting defects.Multi-point corrosion exists in casing and tubing to study the interaction between two pitting pits,it is found that there is a critical value in the spacing between the two pitting pits,and the interaction between the two pitting pits can be neglected when the spacing is greater than the critical value,and the interaction between them should be considered when the spacing is less than the critical value.The spacing between the annular pitting pits has little influence on the residual strength of the casing,and the presence of secondary pits will change the mises stress distribution of the corrosion pits and reduce the residual strength of the.