COLD-SPRAYED Al-COMPOSITE COATINGS ON S135 DRILL-PIPE STEEL

Nine kinds of Al-composite coatings were cold sprayed on the S135 steel. The mechanical properties and microstructures of the coatings were analyzed and the corrosion behavior of the coatings was studied. The surface morphology of the coatings was observed. The porosity of the nine coatings was less than 1.52 %. A proper increase in the Zn powder could reduce the porosity. The thickness of a coating could be increased with an increase in Al2O3 and Zn. The hardness of a coating increased obviously after adding Al2O3. The friction coefficient of a coating decreased with the increase in Zn and Al2O3. The corrosion rate of the coatings decreased with an increase in Al and Al2O3.

Study on Properties of Cold-Sprayed Al-Zn Coating on S135 Drill Pipe Steel

With the gradual depletion of shallow resources, the petroleum industry is developing toward ultradeep wells and high-speed drillings, and the problems of corrosion and erosion failure of drill pipe materials are becoming more and more serious. On the basis of not destroying the excellent mechanical properties of S135 drill pipe steel, three kinds of coatings, 20% Al-80% Zn, 30% Al-70% Zn, and 40% Al-60% Zn, are cold sprayed on S135 steel. The morphology of the coating is observed, and the bonding strength, porosity, hardness, and corrosion resistance of the coating are tested. Results show that the bonding mechanism between the powder particles and the substrate of the three coatings is mainly mechanical occlusion. From the substrate to the coating surface, the hardness value decreases gradually. With the increase of Al powder content, coating bonding strength increases, coating becomes more compact, and porosity decreases. Corrosion test results show that three coatings can protect the substrate. The density of corrosion products on the coating surface increased with the increase of the Al content. Corrosion potential of the three coatings is lower than that of the substrate, and the corrosion rate of the three coatings is lower than that of the substrate.

Investigations of Fatigue Performance of S135 Drill Pipe Steel under Uniaxial Loading

The fatigue life of S135 drill pipe steel was investigated by means of tension-compression loading and torsion loading under uniaxial loading during the fatigue test. The quantitative formulas of fatigue life were obtained by regression analysis method, and the fatigue fracture mechanism was analyzed. The results show that a linear correlation was found between fatigue life and effective stress in the double logarithmic plots. Cracks initiated from the specimens surfaces under tension-compression loading as well as torsion loading. For the tension-compression fatigue and the torsion fatigue specimens, the main characteristics for cracks propagation were striations and sheares ripple marks, respectively.