The Study On Tribological Characteristics Of Surface Coating For The Thruster Drilling Platform

The large-scale exploitation of offshore oil and gas resources has greatly alleviated the current situation of energy shortage in China.As the main mining equipment,the reliability of drilling platform performance has received widespread attention.In the harsh marine environment,the thruster of drilling platform in the fully immersed seawater area will produce serious friction and wear under the impact corrosion of sea water.At the same time,the thruster will be corroded by sea water and attached pollution of marine organisms,which will seriously affect the service life of the propeller.The preparation of a protective coating on the surface of the thruster is the main measure to protect it.The Zn-Al coating is the most widely used metal protective coating.On the one hand,the preparation of a coating on the surface of the substrate can produce mechanical insulation,separating the substrate from seawater.On the other hand,the coating delays or reduces the damage caused by the environment through its own properties.Although the Zn-Al series coatings have made great progress in the field of marine protection,in order to better adapt to the long working cycle of the drilling platform and difficulties in returning to the factory for maintenance,etc.It is found that,The corrosion products of Mg,Zn and Mg,Al are more compact and uniform,which have excellent isolation effect on corrosion medium.TiO₂ can decompose organic compound and protein under ultraviolet radiation,which has good antifouling performance.Thereby,the Zn-35Al-5Mg-15TiO₂ and Zn-35Al coatings were prepared by cold spraying.The tribological characteristics,antifouling and corrosion resistance of different coatings were studied through a series of tests.Before the coating was prepared,in order to fully mix the material particles,useing a ball mill to mixed the powder,then analyzed the microstructure and element distribution of the mixed powder.The results show that the particles are mixed evenly,the particles are distributed independently,and there is no obvious doping phenomenon,which is the typical pseudo alloy powder.In the process of research and analysis,SEM,EDS,Scratch tester,Micro-hardness tester,Friction and Wear tester,White light interferometer,Electrochemical workstation,Spectrophotometer were used to carry out the scratch test,hardness test,friction and wear test,dynamic salt water immersion test,electrochemical test and catalytic degradation test to study the various properties of Zn-Al-Mg-TiO₂ coating and Zn-Al coating,and compared and analyzed the result.The results show that the adhesion of the Zn-Al coating is 22N,and the adhesion of the Zn-Al-Mg-TiO₂ coating is 27N,which has slightly improved.The microhardness of Zn-Al-Mg-TiO₂ coating is 109HV_0.1,increased by 23.9%.After the dry friction and wear test,the friction coefficient of Zn-Al-Mg-TiO₂ coating is 0.2974 and the wear amount is 0.106g.The structure of wear scar is more uniform,the bottom is flat,the wear scar depth is smaller than that of the Zn-Al coating.There are a lot of scratches on the bottom of the wear scar,indicating that The wear mechanism of the Zn-Al-Mg-TiO₂ coating is mainly abrasive wear.After calculating the material loss caused by various factors of the two coatings during the friction and wear test of the two coatings in the simulated seawater salt solution,it is concluded that the corrosion behavior of Zn-Al-Mg-TiO₂ coating and Zn-Al coating in 3.5%NaCl solution will be worse by more obvious friction and wear,and the influence of Zn-Al coating is greater.After 720 hours of dynamic salt water corrosion,a dense passivation film was formed on the surface of Zn-Al-Mg-TiO₂ coating,which effectively slowed down the corrosion rate of the coating.However,the corrosion products on the surface of Zn-Al coating were relatively poor after 720 hours of corrosion.It shows that the addition of Mg can indeed improve the passivation film of the coating and play a role in isolating the corrosive medium.In contrast,the corrosion rate of Zn-Al-Mg-TiO₂ coating is always lower than that of Zn-Al coating during long-term immersion corrosion.The experimental study on antifouling degradation of the coating shows that under ultraviolet radiation,a sample of Zn-Al-Mg-TiO₂ coating can degrade 50 mL methyl blue solution with a concentration of 20mg/L more than 80%within30min,while the Zn-Al coating has not catalytic effect on methyl blue under the same environment.Through the simulation analysis,it is found that under the extreme operating conditions,the stress on the special part of the thruster is greater than the bonding strength of Zn-Al coating on the surface of the thruster substrate,while the bonding strength of Zn-Al-Mg-TiO₂ coating is on the substrate surface is greater than the maximum stress of the coating,indicating that it can provide protection for the thruster of the drilling platform for a longer time under the extrusion and erosion of sea water.