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This work investigated the pitting failure mechanism of S13Cr tubing in a gas well resulting from multiple gas lifts. The causes of pitting corrosion through the use of numerical simulations (CFD) were determined. Electrochemical noise technique was used to explore the process of pitting corrosion. Results show that the chemical elements, inclusions, metallographic structures, and strength of S13Cr tubing meet standard requirements. Scanning electron microscopy, energy-dispersive spectroscopy and X-ray photoelectron spectroscopy were used to analyze the compositions of corrosion products, which mainly consist of FeCO3, Fe2O3, FeOOH, Cr2O3, and Cr(OH)3. Numerical simulations show that a liquid film is formed in the local well section of the inner wall during gas lift. Electrochemical noise revealed a linear decrease in potential noise and a linear increase in current noise, indicating that the adsorption of Cl- on the electrode surface erodes the passivation film. Current and potential transient peaks began to appear and increase, indicating the development of pitting erosion toward a steady state. In the actual production process, S13Cr tubes lead to crack initiation and expansion due to the coupling of mechanical–chemical effects of Cl−, CO2, and O2. [ABSTRACT FROM AUTHOR]

Casing steel is prone to reduced mechanical properties and occurred environmentally assisted cracking finally in sour well environment containing H2S and CO2. The paper mainly researched on the relationship between mechanical properties and hydrogen permeation, exposed casing steel P110 to air, NACE A solution, and simulated formation water containing H2S and CO2 with a stress of 80% yield strength at 60 °C for 168 h, testing its mechanical properties shown strain-aging phenomenon and ductile–brittle transition. The lowest mechanical properties are occurred in the sour well environment, its yield strength, and tensile strength, respectively, reduction 5.0% and 4.7%, while a loss of 41.4% in fracture toughness. With temperature increased from 25 to 60 °C, the hydrogen diffusion coefficient increases by 1.59 times, and there is a mutation in mechanical properties of P110, when the hydrogen diffusion coefficient is 1.64 × 10–4 cm2/s and the subsurface hydrogen concentration is.1.653 × 10–5%. The steel P110 has shown a ductile fracture with toughnest exposed in the air and shown cleavage fracture characteristics exposed to sour environments, indicating that hydrogen permeation has changed the fracture mode from ductile to brittle. This method can be used to test and compute the strength attenuation effect of casing P110 serviced in sour well environments. [ABSTRACT FROM AUTHOR]

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 10 rotations and could be used in the fast prediction of fatigue strength of drilling materials. [ABSTRACT FROM AUTHOR]

The effects of plastic deformation and HS 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 HS (PD+HS). 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 HS, 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is well known that drillpipe failures are a pendent problem in drilling engineering. Most of drillpipe failures are low amplitude-repeated impact fatigue failures. The traditional method is using Charpy impact test to describe the fracture property of drillpipe, but it cannot veritably characterize the impact fatigue property of drillpipe under low amplitude-repeated impact. Based on the Charpy impact and other methods, a repeated impact method and instrument have been proposed to simulate the low amplitude-repeated impact of downhole conditions for drillpipe. Then, a series of tests have been performed using this instrument. Test results demonstrate the drillpipe upset transition area nonhomogeneity is more severe than drillpipe body, which is the key factor that leads to washout and fracture frequently of it. As the one time impact energy increases, the repeated impact times decrease exponentially, therefore, the rotational speed has a great effect on the fatigue life of drillpipe, and it is vital to select a suitable rotational speed for drilling jobs. In addition, based on SEM fractographs we found that the fracture surface of repeated impact is similar to the fatigue fracture, and there are many low cycle fatigue characteristic features on fracture surface that reveal very good agreement with the features of drillpipe fatigue failures in the field. [ABSTRACT FROM AUTHOR]

With the aid of hydrogen permeating devices, the hydrogen permeation behaviors of X52 pipeline steel in NACE A solution with saturated HS/CO were studied under the conditions of different ambient temperatures and pH values, and the hydrogen permeation behaviors of X52 pipeline steel in weld seam zone were comparatively studied. The experimental results show that the hydrogen permeation coefficient value is directly proportional to the time required for reaching the saturation anode current and inversely proportional to the saturation anode current, and the hydrogen permeation coefficient is influenced by the corrosion scales; the temperature is directly proportional to the saturation anode current, and the hydrogen permeation coefficient is influenced by the temperature and corrosion scales, heat-affected zone and matrix zone in NACE A solution with saturated HS/CO at normal temperature. The hydrogen permeation coefficient in weld seam zone is larger than that in heat-affected zone which is further larger than that in matrix zone. [ABSTRACT FROM AUTHOR]

The corrosion behavior of C110 bushing at high temperature and high pressure with a high HS/CO was studied, and a basis for the materials selection of sour gas well bushing was provided in HS, CO and saline coexisting environment. Under acidic condiction, hydrogen atoms greatly entered into the material and caused the material properties changed. Weight loss method was used to study the corrosion rate of hydrogen charging samples and original untreated samples in simulated oil field environment. PAR2273 electrochemical workstation was used to examine the electrochemical performance of samples untreated, hydrogen charging after reacting in autoclave. The corrosion product film was observed through SEM. The experimental results show that sample with hydrogen charging has a much more obvious partial corrosion and pitting corrosion than the untreated blank sample even the downhole corrosion speed of bushing is increased after being used for a period of time. Polarization curve shows the corrosion tendency is the same between sample with or without hydrogen charging and corrosion tendency is reduced by corrosion product film. A layer of dense product film formed on the surface of samples provides a certain protective effect to the matrix, but cracked holes which will accelerate partial corrosion of the sample were also observed. [ABSTRACT FROM AUTHOR]