Study On Mechanical Properties Damage And Corrosion Behavior Of Drill Pipe Body Material Under Wet H 2 S Environment

When exposed to hydrogen sulphide environments, oilfield equipment and pipeline steels will produce hydrogen damage or hydrogen brittlement, which brings to the giant economic loss and human casualties. In order to ensure that oil and gas exploration work safely, reliabley and efficiently, the rsearch of the corrosion behavior and mechanical properties damage of the drill pipe materials in the wet　H2S environment must be carried out. This paper studied the changes in mechanical properties of G105 and 105SS drill pipe materials in wet H2S environment, and the influence of corrosion time on the impact energy, impact curve, impact fracture surface and dynamic fracture toughness.Besides, this paper discussed the impact performance damage rule of 105SS and G105 drill pipe materials in wet H2S environment. In order to explore the mechanism of the mechanical damage of drill pipe materials, the paper measured hydrogen diffusion hydrogen content, hydrogen permeation curves, the morphology structureand thickness of the corrosion scale, and the influence of corrosion scale on the electrochemical performance of samples in the different corrosion time, Those provided reference and technical support for safe drilling and reducing drilling tool failure.The results of mechanical properties tests showed that, in contrast to the original samples with no corrosion, the yield strength, tensile strength and elongation to failure of the same drill pipe samples with four days corrosion not changed much. The impact energy of 105SS sulfur resistant drillpipe was significantly greater than G105 materials. And the impact energy of these two kinds of material decreased to some degree. As immersion time increased, the impact energy of G105 and 105SS dropped substantially. Then, the impact energy gradually kept stable. After 20 days immersion, the impact energy decreased again, oscilloscope Charpy impact curve appeared unstable extension. The proportion of the fibrous region and shear lip region in the fracture surface was also appeared to reduce, then gradually kept stable, and at last, decreased again. The fracture characteristic of G105 and 105SS original samples was toughness fracture with dimples. The number of cleavage plane and river pattern morphology in the perimeter of the dimples increased significantly. The fracture characteristic contained dimples, cleavage plane and river pattern morphology. It belongs to the mixed morphology of micropore aggregation fractures and cleavage fractures. The fracture characteristics convert toughness fractures to quasi-cleavage or cleavage fractures with the increase of immersion time. The dynamic fracture toughness of the drill pipe materials also decreased with increasing immersion time. The rate of crack propagation increased quickly. Besides, the impact toughness and dynamic fracture toughness of 105SS sulfur resistant drill pipe is greater than that of the G105 drill pipe, and descend range was less than G105 drill pipe, so the mechanical properties of 105SS in H2S environment is superior to G105 drill pipe.The diffusible hydrogen measurement results of drill pipe showed that diffusible hydrogen content increased firstly and then decreased with the increase of immersion time. The variation of the relative impact toughness and dynamic fracture toughness loss with immersion time is quite similar with that of hydrogen content with immersion time. It indicated that the mechanical property loss was closely associated with hydrogen content.Corrosion tests in wet H2S environment showed that the effect of immersion time on the morphology of corrosion films is remarkable. As immersion time increased, the thickness of corrosion films and the grains of corrosion films increased gradually. Corrosion film would became more even, compact and continuous. The grains of corrosion film transformed from loose irregular crystal grains to geometry rules crystal grains. The number and size of the grains of corrosion films on the surface of the 105SS sample were smaller than G105. It is concluded that the corrosion-resistant property of 105SS was much better than G105 drill pipe.The corrosion films could block the direct contact of the H2S corrosion medium and metal material base body. The corrosion film with compact and continuous grains lead to a good protection to the drill pipe in the wet H2S environment. The corrosion films also had an effect on the self-corrosion current of the drill pipe. The self-corrosion current of the G105 and 105SS drill pipe increased first then decreased and then increased with increasing immersion time.