| Offshore oil and gas platform is the most important equipment for the development of offshore oil and gas resources,and its supporting structure usually spans the thermocline.The corrosion factors such as temperature and dissolved oxygen in the thermocline change sharply in the longitudinal direction,which makes the support structure of offshore oil and gas platform seriously corroded,shortens the service life of offshore oil and gas platform,and causes huge economic losses.At present,the corrosion characteristics and mechanism of long-scale metals in thermocline are not clear,and there are many difficulties in the study of metal corrosion in real thermocline.Based on this,a thermocline simulation device is designed.The corrosion experiment was carried out by combining the simulation device with the test method of seawater chemical elements and the research method of metal corrosion,the main content of this research includes the following parts:(1)A device for simulating and measuring thermocline in seawater.Based on the research background of severe corrosion of oil and gas platform supporting structure in thermocline,a seawater thermocline simulation and measurement device is designed,which includes three parts: main structure,temperature control system and sampling system.The temperature of the top and bottom of the seawater is controlled by the temperature control system to generate the simulated thermocline in the main structure.The seawater samples with different depths of the simulated seawater thermocline are taken out by the sampling system for the determination of physical and chemical parameters.(2)The physical and chemical parameters of simulated seawater temperature jump are measured.The physical and chemical parameters needed to be measured include temperature,pH value,dissolved oxygen and nutrients.The temperature was measured and recorded in real time by the temperature control system.The pH value,dissolved oxygen and nutrients were determined by chemical methods.(3)Research technology of metal corrosion in simulated seawater thermocline.In order to study the corrosion behavior of long metal in thermocline,a detachable chain electrode was designed.Through the exposure test of chain electrode in simulated seawater,the corrosion characteristics and mechanism of metal in seawater thermocline were studied by means of electrochemical testing technology,corrosion morphology observation and weight loss calculation.In order to verify the effectiveness of the simulation system,the corrosion of long-scale metals in simulated seawater thermocline was studied with E690high-strength steel developed in China as test material,the main conclusions are as follows:(1)In the process of the experiment,temperature,pH,dissolved oxygen,active silicate and phosphate showed gradient change except for three nitrogen,and the change trend was basically consistent with that in the real thermocline.(2)During the whole experiment,galvanic corrosion was found in the whole chain electrode.In the first stage(0-14d),galvanic corrosion is not the main cause of corrosion;in the second stage(14-27d),a macro corrosion cell is formed in the chain electrode,and galvanic corrosion has an important impact on the overall corrosion;in the third stage(27d-66d),it is the corrosion mode of large cathode and small anode,and the galvanic effect makes the small anode seriously corroded.(3)Due to the limited protective effect of galvanic action on the cathode region,and the corrosion products are loose and have no protective effect on the substrate,the electrode with negative potential in the cathode area also suffers serious corrosion.The development of the simulation device expands the research scope of metal corrosion in marine environment,and provides theoretical basis and data support for the design,material selection and formulation of anti-corrosion standards of marine engineering equipment. |
PDF Full Text Request