Research On Stress Corrosion Behavior Of Typical Low Alloy Steels For Petroleum And Petrifaction In Wet Hydrogen Sulfide Environment

Many machinery and equipments of petroleum natural gas storage and transportation, petroleum refine process and other correlation industries selected the low alloy steels widely, which used in wet hydrogen sulfide environment. Recently, along with the deepness exploitation of nation crude oil and increase of Middle East crude oil importation, the wet hydrogen sulfide (H2S) stress corrosion cracking of low alloy steels were extruded increasingly and became the key problem for production branch and scientific research institution to be studied and resolved. As the complexity of stress corrosion influence factors, some problems deserved to be lucubrated and discussed.This paper selected three representative low alloy steels that widely used in petroleum and petrifaction industry, they were heat exchangers tube steel 08Cr2AlMo, oil and natural gas pipeline steel X70 and pressure vessel steel 16MnR. Through the slow strain rate testing(SSRT) and corrosion testing, the H2S stress corrosion behavior of 08Cr2AlMo steel, X70 pipeline steel and its welded joints were presented. Based on the electrochemistry corrosion testing, the H2S stress corrosion behavior of 16MnR was discussed, and the corrosion cracking behavior of 16MnR steel welded joints surface made of nanometer composite chemistry plating and nanometer composite electrochemistry plating in wet H2S environment were tested and studied. Besides, Some advanced testing techniques such as the metallurgical microscope(MM), scanning electron microscope(SEM), energy dispersive spectrum(EDS) and electrochemistry station were also used for observing and testing the microcosmic structure, component and surface morphology. Simultaneity, the methods of numerical value calculating, regression analysis and computer embedded the studies too. Some mathematical models were established.The conclusions of this research can be generalized as:1. Based on the uniformity design method, the SSRT of 08Cr2AlMo steel, X70 base metal and its welded joints steel in different concentration of H2S, concentration of Cl- , pH and temperature were tested. After analysed the microcosmic morphology by SEM, determined the nature of stress corrosion sensitivity and calculated the stress corrosion sensitivity index in different examination environment. Based on the regression analysis software, the intercross mathematics model of stress corrosion sensitivity index of 08Cr2AlMo steel , X70 base metal and X70 welded joints steel and medium parameters (concentration of H2S, concentration of Cl-, pH and temperature)were established.2. The differenences of X70 base metal and its welded joints in SSRT corrosion testing were: the stress corrosion sensitivity index of X70 welded joints priority to the base metal, and the rupture position existed in heat affected zone(HAZ) and welding line, which can be indicated that the stress corrosion sensitivity of X70 welded joints priority to the base metal even more, which provided an observation point for investigating the pipeline steels H2S stress corroion cracking further.3. The polarization curves of 16MnR steel in different concentration of H2S, Cl-, pH and temperature were tested by vitue of zeta potential speed scaning technics. The electrochemistry corrosion behavior of 16MnR steel in different concentration of H2S, Cl-, pH and temperature were studied. Based on the different wet H2S stress corrosion sensitivity potential section of 16MnR steel, the static state safegy function figure of 16MnR steels in different influence factors was constructed.4. The polarization curves of 16MnR steel in different stress and strain states were tested, the influences of stress and strain on 16MnR steel in H2S environment were studied, and the influences of potential on the 16MnR steel stress-strain curve and sensitivity were also described. The possibility of 16MnR steels wet H2S stress corrosion cracking and correlation mechanisms were also investigated.5. In this paper, the excellent constitutes and technics of nanometer composite electroless plating and nanometer composite electroplating were selected by examnination. An investigation was made on the effects of various factors on the plating nano-TiO2 content, aggradation velocity and plating density, and the organize and structure morphology of samples disposed or not were performed by means of metallurgical microscope(MM), scanning electron microscope(SEM). The H2S stress corrosion performance of 16MnR welded joints treated with surface nanocrystallization were investigated by constant load tensile examination. The results of this study showed that the stress anticorosion of nanometer composite electroless plating is the 1.5 times of general plating, nanometer composite electroplating is the 1.7 times of general plating, and the wet H2S stress anticorosion of nanometer composite electroless plating was higher than the nanometer composite electroplating, which the value exceeded the national standards. This paper provided a science basis on nanometer composite electroless plating and nanometer composite electroplating applied for run equipments in wet H2S environment.The author considered that what we studied on the low alloy steels and the rules from the examination provided a science basis to solve the stress corrosin cracking of equipments in wet H2S environment, and also had the significant reference value.