Junying Hu

Fatigue Strength Prediction of Drilling Materials Based on the Maximum Non-metallic Inclusion Size

Abstract In this paper, the statistics of the size distribution of non-metallic inclusions in five drilling materials were performed. Based on the maximum non-metallic inclusion size, the fatigue strength of the drilling material was predicted. The sizes of non-metallic inclusions in drilling materials were observed to follow the inclusion size distribution rule. Then the maximum inclusion size in the fatigue specimens was deduced. According to the prediction equation of the maximum inclusion size and fatigue strength proposed by Murakami, fatigue strength of drilling materials was obtained. Moreover, fatigue strength was also measured through rotating bending tests. The predicted fatigue strength was significantly lower than the measured one. Therefore, according to the comparison results, the coefficients in the prediction equation were revised. The revised equation allowed the satisfactory prediction results of fatigue strength of drilling materials at the fatigue life of 107 rotations and could be used in the fast prediction of fatigue strength of drilling materials.

Corrosion Behaviors of Q345R Steel at the Initial Stage in an Oxygen-Containing Aqueous Environment: Experiment and Modeling

The ingress of oxygen into pressure vessels used in oil & gas production and transportation could easily result in serious corrosion. In this work, the corrosion behaviors of Q345R steel at the initial stage in 1 wt.% NaCl solution were investigated using electrochemical techniques. The effects of oxygen concentration, temperature and pH on corrosion behaviors were discussed. Simultaneously, a numerical model based on the mixed potential theory was proposed. The results show that the proposed model accords well with the experimental data in the pH range from 9.0 to 5.0. In this pH range, the oxygen reduction reaction, H+ reduction, water reduction, and iron oxidation can be quantitatively analyzed using this model. However, this model shows a disagreement with the experimental data at lower pH. This can be attributed to the fact that actual area of reaction on the electrode is much smaller than the preset area due to the block effect resulted from hydrogen bubbles adsorbed on the electrode surface.

Effect of Plastic Deformation and H2S on Dynamic Fracture Toughness of High Strength Casing Steel

The effects of plastic deformation and H2S on fracture toughness of high strength casing steel (C110 steel) were investigated. The studied casing specimens are as follows: original casing, plastic deformation (PD) casing and PD casing after being immersed in NACE A solution saturated with H2S (PD+H2S). Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness (JId) was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows: the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.

Stress corrosion cracking of high-strength drill pipe in sour gas well

In high sour gas reservoir drilling process, it happens occasionally that high-strength drill pipe suffers brittle fracture failure due to stress corrosion cracking, and poses serious hazard to drilling safety. To solve this problem, this paper studied the stress corrosion cracking mechanism and influencing factors of highstrength drill pipe in sour environment with hydrogen permeation experiments and tensile tests. We simulated practical conditions in laboratory and evaluated the stress corrosion cracking performance of the high-strength drill pipe under conditions of high stress level. For the problems occurring in use of high-strength drill pipe on site, the paper proposed a technical measure for slower stress corrosion cracking.