Investigation On Laser Surface Hardening Of Oil Tube Inwall

With the exploiting of the oil deposit, the composite water cut of the oil wells is ascendingdrastically, the eccentric wear condition in oil wells is becoming worse and worse in most oilfields of China. Amount of maintenance work and the fabricating cost are ascending with theservice interval of the wells becoming shorter caused by eccentric wear. Centering device andantiseptic wear proof coating are used for prohibiting eccentric wear, and the problems such ascomplex operation and environmental contamination exist with some effectiveness. 5kW laserequipment and light guiding system was used for helix hardening on tube inwall to elevate theantigalling ablity of the tube.Firstly the coating composite and the ballmill process are defined, and the laser coating aremanufactured by using orthogonal design method which can optimize the three variations.Experiment approves that the coating has higher ability of coating forming and light absorbingwith grain size becoming smaller and evenly. In the defined extent, the coating with 7.5% Y2O3,5% soap clay and 3hour's ballmilling is the best. Inwall coating system is manufactured using thehigh speed rotate pulverizing principle to coating the tube inwall.The laser melting effects of four different surface states (blasting and coating, cloud burstingand coating, primary and coating, primary) are tested. The result approves that the surfacehardness of laser melting layer after blasting and cloud bursting can be as 120% higher as that ofthe base steel. And the ability of getting thicker melted layer of the states after blasting and cloudbursting is lager as much as 15% than the original state in the require of forming smoothly.Compare the blasting and cloud bursting process, cloud bursting sample has a better meltedforming. Cloud bursting is the best preprocess for laser melting.Metallographic examination is done to tube steel and melted zone, and the base metal has atriaxial feature of banded microstructure in axial direction, mainly composed by ferrite andpearlyte. The microstructure becomes obviously fine after the laser melting. Melted zone is mainlycomposed of panel martensite and residual austenite, and the phase change zone is mainly composed of acicular martensite and ferrite. Banded microstructure feature is resided in both phasechange zone and high temper zone. Microhardness and electrochemistry corrosion testingapproved that, the medium microhardness declines negligibly, and the corrosion resistance ascendsin some degree with the scaning power ascending.Wear test of ordinary tube and hardening tube is analyzed by means of weight loss, SEM,microhardness and electrochemistry corrosion testing, it approve that: helix hardening tube has abetter wear resistance then ordinary tube, and the hardening tube with higher scanning power andsmaller pitch has better wear resistance than that with lower scanning power and bigger pitch. Themechanism of helix hardening is that: the helix hardening zone which has high wear resistance andanticorrosion ability has a protect effect to the primary zone, the weight loss speed of primary zoneis decreased evidently due to the only corrosion function, then the galling speed of the whole tubeis decreased evidently.