Study On The Preparation And Performance Of Thermal Spraying Aluminum-based Anticorrosive Coating For Water Riser Sleeves

The casing pipe is a key component for ensuring the safe and smooth operation of offshore drilling operations.At the same time,it is a weak link in the entire drilling system.The casing pipe faces severe corrosion in the marine environment,which has an important impact on the safe operation of the drilling system.Therefore,the protection of the water-proof casing is very important.At present,the main protective measures include surface-coating protective paint and thermal spray anti-corrosion coating.The surface-painted protective paint does not meet the requirements for long-term service.Thermal spraying has the characteristics of high spraying efficiency and low comprehensive application cost,and is an efficient surface strengthening technology.It is of great research value to use flame-spraying technology and supersonic arc technology to spray metal anti-corrosion coatings on the outer surface of the casing pipes to extend the service life of the casing.After investigating the spraying materials and coatings of thermal spray marine drilling platforms at home and abroad,combined with the failure mechanism and service performance requirements of the casing pipes,three kinds coatings of Al,Al-Cu and Al-Si were prepared by flame spraying technology.The supersonic arc spray technique was used to prepare two coatings of A1 and Al-Zn.The salt spray test was carried out on the sprayed coatings and the test samples were characterized.The flame sprayed Al,Al-Cu and Al-Si coatings' powders are fully melted,the structure is uniform,and there are no obvious defects such as through-holes.The Vickers microhardness of the three coatings increases sequentially.Supersonic arc sprayed A1 and Al-Zn coatings have a uniform structure,and there are no obvious defects such as unmelted wire,oxide and macropores in the coating.In the neutral salt spray experiment,the three flame spray coatings exhibited similar microscopic corrosion morphology,mainly producing porous particles and crack germination expansion.The corrosion products were mainly Al(HO)3,of which only Al-Si coating was still retained a similar morphology to the sprayed coating until 168 h.After continuous salt spray corrosion,the arc sprayed A1 coating was mainly Al(OH)3 in the corrosion product,and a large amount of agglomerated porous spherical matter was generated on the corroded surface.After continuous salt spray corrosion of the arc sprayed Al-Zn coating,the corrosion product contained a small amount of white flocculating corrosion product Zn5(OH)gCl2·H2O and Zn6Al2(OH)16(CO3)3·4H2O,the corrosion surface had a large number of sheet-like structures stacked and agglomerated,and acicular corrosion products were formed.At the same time,the two arc spray coatings were sealed and found that the presence of the sealing agent can effectively reduce the degree of corrosion of the coating surface.The surface of the two coatings after sealing was almost not damaged by salt spray corrosion.Electrochemical test results showed that the three flame spray coatings and the two arc spray coatings showed good electrochemical performance in the 3.5 wt%NaCl solution after salt spray test.Under long-term salt spray conditions,the Al-based coating can physically and electrochemically protect the steel matrix.