An Investigation Of Corrosion Performance Of Aluminum Alloy Drilling Pipe Materials

Aluminum alloy drill pipes play more and more important role in oil drilling,offshore drilling, polar drilling and continental scientific deep drilling because of theirhigh specific strength, low density, non-magnetism and good low temperatureproperties, for which they find a broad application prospective. Aluminum alloydrill pipes are made of7075and2024, which are heat-treatable and of high strength.They’ve also found partial applications in continental scientific drilling and polarscientific drilling because of their good mechanical properties. However, aluminumalloys are susceptible to the corrosion environment containing chloride ion(Cl-).Aluminum alloy drill pipes will inevitably face corrosion problems when they areused in environment of marine drilling, saliferous strata and salty drilling fluid. Soit’s very important to investigate the corrosion performance of7075and2024aluminum alloy drill pipes in environments containing Cl-. This work also carriedout the investigation of corrosion resistance of7075aluminum matrixcomposite(AMC) incorporated with in situ TiB2particulate, which has potential highstrength and high wear resistance. Quantitative potentiodynamic polarization test wasapplied to evaluate the corrosion susceptibility and corrosion rate of the three kinds ofmaterials. Scanning electron microscopy(SEM), energy dispersive spectrum(EDS)analysis and electron back scatter diffraction(EBSD) were used to analyze thecorrosion mechanism of the above three materials and the influence of alloy’scomposition, phase structure, grain boundary character distribution(GBCD) anddeformed grain stored energy on corrosion behaviors.The investigation showed that the corrosion performance of2024aluminumalloy drill pipes is better than that of7075aluminum alloy drill pipes. And it wasfound that the corrosion performance of different parts of the drill pipe differedobviously because of the difference of the corresponded extrusion ratio. As far asthe corrosion mechanism concerned, the corrosion forms of7075aluminum alloy drillpipe include pitting, intergranular corrosion and exfoliation corrosion, while2024aluminum alloy drill pipe include only two corrosion forms which are pitting and intergranular corrosion. The difference of the corrosion performance between thetwo materials is mainly due to the difference of alloy’s composition and theexperienced heat treatment.The corrosion rate of aluminum matrix composite7075-TiB2corresponded withthe proportion of TiB2particles. Corrosion behavior of the composite material ismainly related to the changes of dislocation density caused by in situ TiB2particles.Corrosion of this kind of aluminum matrix composite features pitting corrosion andintergranular corrosion. And the pitting corrosion occurred intragranularly. Theselective pitting of aluminum matrix composite7075-TiB2composite is characteristicof intergranular asymmetry, mainly because of the different densities of localdislocation caused by the mismatch of coefficient of thermal expansion between theof TiB2particles and the aluminum matrix. The interfacial corrosion between theCu-rich intermetallic compound and aluminum matrix is caused by electrochemicalreaction resulting from the uneven distribution of components, the fall of which leadsto micro-pitting.The selective characteristic of the intergranular corrosion of the aluminum alloysand aluminum matrix composites is mainly related to the grain boundary characterdistribution. It was found that high angle grain boundaries were prone to corrosionattack, while the special grain boundaries and low-angle boundaries were resistant tocorrosion.