Study On The Influencing Factors On Wet H₂S Stress Corrosion Cracking Test Of Oil Tube Shanghai Jiao Tong University

With the rapid development of economy and society, the exploitation and distribution of oil resources have stepped into the peak point of construction period using oil well tube with the development trend of large diameter, high steel grade and corrosion resistance. Performance of H2S corrosion resistance must pass the H2S stress corrosion test of NACE standard. However, there are many factors influencing the course of the test, resulting in significant reduction of test stability, while current research in this area is limited. In this paper, the relationship between surface quality and test result was studied by using the basic principles of orthogonal experiment and fracture mechanics. Then, the relationship between stress factor and test result was studied based on FEA and orthogonal experiment. Finally influencing factors were optimized in order to improve the stability of the corrosion test.The surface quality of the specimen was mainly studied from two ways including surface roughness and surface cracks chosing BG110S tube as the research object. The influence of grinding parameters on surface roughness was analyzed through orthogonal experiment and the linear relationship between H2S corrosion rate and surface roughness was obtained. It was obtained the least influencing grinding condition is vs=30m/s, vw=230r/min, ap=0.010mm, f=0.250mm/s and D=180. The H2S corrosion cracking process was modeled based on fracture mechanics to analyze the influence of surface crack on corrosion test. And the linear inverse relationship between crack length & depth and corrosion cracking life, having square inverse relationship with load was obtained.The thermal-mechanical coupling model for single abrasive grain cutting process was built based on FEA software Deform, calculating residual stress under different grinding conditions. The model was verified correctly and the influence of grinding parameters on surface roughness was got through orthogonal experiment. The square inverse relationship between corrosion cracking time and surface residual stress was fitted and obtain that the least influencing grinding condition is vs=30m/s, vw=460r/min, ap=0.010mm, f=0.750mm/s and D=180.Considering surface quality and residual stress, the most optimized grinding condition is vs=30m/s, vw=460r/min, ap=0.010mm, f=0.250mm/s and D=180. The surface roughness is below 0.300μm and surface residual stress is below 160MPa, increasing the stability of H2S stress corrosion test upto 90%.The most optimal heat treatment has been proved to be quenching and tempering according to H2S stress corrosion test. That is water-cooling over 60s after heating to 900-950℃and holding for 120s firstly, then air-cooling to room temperature after heating to 650-700℃and holding for 120s. In this way, Specimen can get good comprehensive mechanical properties and compressive surface residual stress without surface cracks. So the stability of H2S stress corrosion test increases significantly. A proving ring automatic loading system based on closed-loop control was designed independently in order to reduce the aritificial errors and nonlinear error of proving rings.Influencing factors of H2S corrosion test was found, the influencing law was analyzed, corrosion test process was optimized and stability of test was greatly enhanced. So that production efficiency of H2S corrosion- resistant pipe was improved and production cycle was shorten. Also the research provides foundation for further study and optimization for the production process of H2S corrosion-resistant oil well pipes.