The effects of surface roughness on the corrosion mechanism of HP-13Cr stainless steel in the dynamic aggressive oilfield environment were investigated through surface analysis, weight-loss measurements, and computational fluid dynamics simulations. The results showed that the surface roughness mainly changed the fluid state at the metal/solution interface. With the increase in the surface roughness, the vortex was more likely to form at the trough of the waves. The vortex could result in the deposition process and inhomogeneity in the thickness of the oxide film. The pitting corrosion occurred more easily. Furthermore, the temperature and CO2 pressure obviously facilitated the corrosion rate.

The hydrogen embrittlement susceptibility of electron beam melted Ti-6Al-4V alloy (ET) was compared with that of conventional wrought alloy (WT). Hydrogen permeation, electrochemical, and slow strain rate tensile tests as well as surface observation were conducted under a simulated sea environment. The results show that the hydrogen embrittlement susceptibility of ET is lower than that of WT, which can be attributed to the intense texture of ET with a smaller specific surface area of grain boundary, preventing hydrogen permeation. Moreover, with increasing depth of the ocean, the hydrogen embrittlement susceptibility of both ET and WT TC4 alloys increases considerably. This reduced hydrogen embrittlement resistance can be attributed to the degradation of the passivation film, accelerating the permeation flux of hydrogen.

The corrosion and passive behavior of HP-13Cr stainless steel (HP-13Cr SS) in formate annulus protection fluid was investigated. HP-13Cr SS exhibited good passive behavior in clean formate annulus protection fluid, which was attributed to a thinner and more dense passive film mainly composed of Cr2O3. In the formation water solution, the passive film was composed of metastable Cr(OH)3, which was explained by the isoelectric point theory, resulting in the deterioration of the passive behavior of HP-13Cr SS. When the formation water penetrated the formate annulus protection fluid, a large number of loose FeCO3 particles formed in the corrosion scales, thus HP-13Cr SS suffered severe corrosion. Therefore, avoiding formation water penetrating the formate annulus protection fluid is conducive to improving the service life of HP-13Cr SS oil tubes in extremely aggressive environment.

The dissolution–ionization–diffusion–deposition (DIDD) model was used for developing a corrosion–resistant stainless steel (SS) by the means of alloying and the guidelines for the process were proposed. The novel HP–13Cr–Cu SS was designed to resist corrosion in H2S–containing geothermal environment. The results indicated that the preferential deposition of CuS promoted the heterogeneous nucleation rate of Cr2O3, FeCr2O3, and FeS, which formed denser corrosion product layer. As a result, this alloy exhibited a low corrosion rate and a high sulfide stress cracking (SSC) resistance. The results were consistent with the theoretical calculation conducted by the DIDD model.

As a common heat exchanger in the field of petroleum industry, the structure of reboiler is extremely complex, in which U-tube bundle is the key part. The N-Methyldiethanolamine medium contains hydrogen sulfide, carbon dioxide and other acidic gases, which is highly corrosive. In addition, due to the contact with a variety of materials, there is the risk of galvanic corrosion. Firstly, the galvanic corrosion behavior of reboiler materials in solution was studied by numerical simulation, and it was found that the corrosion of U-tube bundle was serious. Then, the combined protection design of coating and sacrificial anode is used to protect the reboiler U-tube bundle from corrosion. The numerical simulation results show that the combined protection of coating and sacrificial anode has a good effect. This numerical simulation method also provides an effective idea and method for the corrosion research of super complex structures such as reboiler.

Electrochemical noise (EN) analysis was used to investigate the influence of the beta phase on AZ91D alloy pit corrosion. The results revealed that the beta phase was involved in AZ91D alloy pit corrosion in two ways: (1) during the pit initiation process, the beta phase acted as a galvanic cathode. This beta phase lowered the rate of nucleation but increased the transition ratio of nucleation to metastable pits. (2) After the formation of stable pits, the beta phase was an anodic barrier that lowered the probability of pit growth, demonstrating that the pits formed on the AZ91D alloy at this point were less likely to become stable compared with T4 heat-treated AZ91D alloy. Therefore, pit cavities developed were larger than those on T4 heat-treated AZ91D alloy.

The flow-accelerated corrosion (FAC) mechanism of HP-13Cr SS in an extremely aggressive oilfield environment was investigated through surface analysis, weight loss measurements, and computational fluid dynamics simulations. The results show that metal/solution interface is divided into a stagnant layer and a boundary layer. The flow can barely reduce the thickness of the boundary layer. Moreover, the limited thickness of the stagnant layer is mainly due to the surface roughness. Consequently, the diffusion of cations toward the bulk solution is accelerated, and the corrosion rate is increased. Furthermore, the temperature and the CO 2 pressure are crucial factors in promoting the FAC.

Through electrochemical and surface analysis,the composition,semi-conductive property and electrochemical performance of the passive film formed on selective laser melting stainless steel 316L(SLM SS316L)and wrought SS316L in the deep sea environment were analyzed,respectively.Results indicated that the corrosion resistance of SS316L can be enhanced by the SLM process,which is attributed to the greatly smaller grain size and higher density of grain boundaries.Grain boundary,i.e.metallurgical defects,enhances the dissolution of SS316L and releases a large quantity of Cr3+ions at the interface.Then Cr(OH)3 precipitated and dehydrated to produce much more stable oxides Cr2O3.As a result,a thin and compact passive film formed on the SLM SS316L,which then suppressed localized corrosion and resulted in high corrosion resistance.

The well completion process in oil and gas industry, aiming to build effective exploitation, is divided into acidizing and formation water production process. Oxide scale (OS) formed on the inner wall of the HP-13Cr stainless steel tubes during the hot extrusion process changes the surface roughness. The effects of OS on the corrosion of HP-13Cr stainless steel during well completion process were studied by corrosion measurement, spectra analysis, microscopic observation and numerical simulation. The results indicate that the OS make no change of phase distribution and element composition of corrosion scale, while the increasing OS roughness is the dominant factor for accelerating corrosion rate during the well completion process. In acidizing process, the greater surface roughness OS of HP-13Cr stainless steel increases the corrosion rate obviously due to a larger interfacial area in contact with the aggressive environment. During subsequent formation water production process, the turbulence eddy, formed at locations characterized with greater surface roughness OS, can deteriorate the corrosion scale and accelerate the mass transfer of the corrosive species, resulting in more serious corrosion.

The influence of rare earth element (RE) Y on the microstructure and corrosion behavior of extruded AZ91 Mg alloy was surveyed via morphology characterization and corrosion performance measurements. The results indicate the corrosion resistance of the transversal section of AZ91 Mg alloy containing Y was improved compared with AZ91 Mg alloy without Y. The corrosion resistance of the longitudinal section of AZ91 Mg alloy with Y was lower than that of AZ91 Mg alloy without Y. The change of corrosion resistance can be attributed to the dispersion and volume fraction of the second phase, the effect of cathodic reduction rate, and the refined second phase.

A bursting incident occurred in a 45-degree elbow of a natural gas gathering pipeline in an oilfield. The failure analysis was performed by means of corrosion morphology observation, corrosion products analysis, and computational fluid dynamics (CFD) simulations. The results showed that a radical change in the fluid state at the 45-degree elbow due to its climbing structure and formation a region of low flow velocity, high pressure and high turbulence kinetic energy, which promoted the condensation of water vapor containing CO2. Then the corrosive water droplets flowed back under the action of gravity and accumulated at the junction between the elbow and horizontal pipeline. In such a corrosive medium, electrochemical corrosion was preferred for 20 steel. In addition, the junction of the horizontal pipe and the inclined pipe exhibits higher structural stress concentration, resulting in increased corrosion thinning. Finally, the failure of the pipeline can be attributed to the synergistic effect of electrochemical corrosion and stress accelerated corrosion.

A new prediction model for pitting corrosion damage considering both pit initiation and pit growth was presented. The pit initiation was modeled based on a combination of the Sridhar model and Macdonald model, and the critical potential was redefined at the same time. The pit initiation time can be divided into the time in which the open circuit potential (OCP) exceeds the repassivation potential (Erp), and the pit induction time, when OCP > Erp. The pit growth was modeled using the Markov process and extreme value statistics were used to describe the maximum pit depth distribution. If the time-consuming pit initiation process is neglected, it results in unacceptable errors in the pit growth kinetics parameters obtained. Thus, an acceleration method, the pre-initiated pits method, was developed to eliminate this negative effect. The proposed model was validated using experimental data on the pitting corrosion of 304 stainless steel (SS) and reproduces the experimental observations with high fidelity. (C) 2019 The Electrochemical Society.

The nature of corrosion scales formed on HP-13Cr stainless steel (HP-13Cr SS) in the extremely aggressive environment was investigated by means of microstructure characterization and high-temperature-high-pressure electrochemical measurements. The results of these studies indicated that the precipitation of Cr(OH)(3) is the dominating factor affecting on the formation of corrosion scales, and its effect can be categorized based on two compromising aspects. On the one hand, Cr(OH)(3) precipitation contributed to the increase of scales thickness. On the other hand, it inhibited the precipitation of FeCO3 due to the hydrolysis of Cr3+. Because of these reasons, the corrosion scales undergo significant microstructural changes, i. e., from monolayer (95 degrees C/2.8 MPa) to bilayer (120 degrees C/3.2 MPa and 150 degrees C/3.6 MPa), then to single layer (180 degrees C/3.8 MPa). Therefore, the corrosion-resistance performance of corrosion scales decreased with increasing temperature and CO2 pressure, wherein the decreasing pitting potential and repassivation potential accompanied with the increasing density and diffusivity of acceptor in the scales.