Severe Localized Corrosion Research Articles

(Invited) In-Situ Liquid Phase TEM Studies of Corrosion Initiation in Aluminium Alloys

Aluminium alloy 2024-T3 (AA2024-T3), widely applied in aerospace industries, may suffer from severe localized corrosion as a result of its relatively complex and heterogeneous microstructure. The corrosion initiation in such a critical alloy is governed by dynamic processes that take place at the nanoscale. A thorough understanding of the sequential stages of corrosion initiation is of pivotal importance to developing efficient inhibition strategies and demands high resolution techniques along with the ability of real-time recording of nanoscopic events.However, to date, it has not yet been possible to unambiguously show the morphological and electrochemical characteristics during local corrosion of AA2024-T3. In particular, local corrosion initiation linked to nano-/microstructural heterogeneities, intermetallic particles (IMPs), take place relatively fast and at the nanoscopic scale, rendering the study of the early stages of corrosion experimentally virtually impossible until now. Herein, we show, for the first time, the dynamic evolution of site-specific local corrosion of AAs from early surface initiation to depth propagation at the nanoscale using a dedicated in-situ liquid phase-transmission electron microscopy (LP-TEM) experimental facility.Transmission electron microscopy (TEM), capable of revealing microstructural and compositional variations in alloys at atomic and nanoscopic scale, has been applied widely in corrosion studies but mostly ex-situ and quasi in-situ. These approaches are not straightforward as artefacts and contaminations might be introduced into the system during the ex-situ and quasi in-situ experiments, including dehydration of surfaces and therefore may not fully represent the real conditions. With recent technological advances, thanks to the development of dedicated microelectronic mechanical systems (MEMS), it is now possible to fabricate components like nanoreactors (NRs) to study complicated corroding systems at the nanoscale in-situ. In fact, NRs employed in TEM studies enable to monitor morphological and compositional evolutions in materials in-situ as a result of interaction with aggressive environments like a gas or liquid.In this study, we put efforts into providing direct evidence for the nanoscopic role of intermetallics in AA2024-T3 localized corrosion through quasi in-situ TEM and in-situ LP-TEM approaches. Quasi in-situ studies were implemented by intermittently exposing the Argon ion-milled thin samples to 0.01 M NaCl solution. For in-situ LP-TEM, the real TEM specimens (lamellae) were first fabricated out of regions of interest with a FEI Helios focused ion beam. Then, the lamellae were transferred successfully to home-made NRs using an easy-lift technique. The NRs, equipped with an electrochemical set-up, were specially designed for corrosion studies. A Cs-corrected FEI Titan TEM was employed to perform real-time studies in scanning TEM (STEM) mode. Although a good resolution is still a major challenge for in-situ LP-TEM, the results revealed that intermetallic phases regardless of their types are active and prone sites to localized corrosion attack themselves and the observations finally show and elucidate initial stages of IMP-induced pitting corrosion and copper redistribution mechanisms in AA2024-T3.

Application of EIS to Assess Microbiologically Influenced Steel Corrosion in Marine Fouling Crevice Conditions

Microbiologically influenced corrosion (MIC) can cause severe degradation of civil infrastructure. Recently, severe localized corrosion of steel H-piles submerged in a brackish natural water in a Florida bridge was associated with MIC and fouling (Permeh et al., 2017). The localized corrosion cells/pits were of up to 3" in diameter and penetrated through the steel thickness. Microbiological and chemical analysis of the water samples showed a high population of sulfate reducing bacteria (SRB) and a high concentration of sulfate ions amongst other nutrients. The steel piles had noticeable heavy marine growth which were thought to have an effect on the corrosion process by supporting biofilm development, creating localized corrosion and differential aeration cells (Little et al, 2007). In the work described here electrochemical impedance spectroscopy (EIS) was conducted to characterize the development of biofilm in association with fouling crevice environments.Electrochemical impedance spectroscopy (EIS) has been widely used to assess the electrochemical properties of corrosion systems and has been applied to assess physical biofilm conditions for microbiologically influenced corrosion (MIC) (Mansfeld , 2005). EIS measurements over a wide range of frequencies can be used to identify the electrical characteristics associated with the biofilm and the steel substrate. Both laboratory and field exposure tests were conducted. Field exposure tests included long term exposure (~300 days) of steel coupons at a Florida bridge site that sustained macro- and microfouling organisms. Laboratory tests were conducted in nutrient-rich test solutions inoculated with sulfate reducing bacteria (SRB) in either de-aerated or naturally aerated conditions as well as with idealized crevice geometries. EIS testing was made at the OCP condition with 10 mV AC perturbation voltage from frequencies 100 kHz > f >100 mHz.EIS of the specimens inoculated with SRB and with crevices resulted in impedance responses with multiple loops in the Nyquist diagram. Fitting of the impedance response to equivalent circuit analogs were made to identify biofilm, surface layers, and the steel interfacial characteristics during the experimental exposure (Permeh et al.,2019). For non-crevice specimens without SRB inoculations, the impedance response related to the solution resistance, steel interfacial capacitance and charge transfer resistance, characterized by the Randles circuit. However, for the inoculated specimens, impedance dispersion at high frequencies (sometimes showing a loop in the Nyquist diagram) on first approximation was related to the capacitive and resistive characteristics of the biofilm. In crevice environments, a more complicated behavior arose due to uneven current distribution and heterogeneous impedance within the crevice. The impedance behavior for the porous and laminate crevices can be characterized by multiple time constants associated with the crevice outer material, steel interface, and the current distribution effects in the crevice that can be considered by treatments such as a transmission line. In the inoculated non-crevice specimens, the high frequency impedance dispersion was more readily apparent in the Bode phase angle plot. In that representation, the impedance initially showed a uniform valley with a distinct trough between 10 and 100 mHz. With time, two unique troughs developed at frequencies below 1 Hz (Figure 1) for the inoculated specimens. An increase in capacitance was attributed to biofilm growth.In part to provide a quantitative comparison of the overall impedance of the systems (despite the complicating factors for the crevice specimens), on first approach, the total impedance at 100 mHz (|Z100mHz¬|) was compared. The differences in the total impedance for the various test conditions would reflect the resistive and capacitive electrical behavior of the electrolyte, biofilm, and the steel interface that in turn are directly or indirectly related to SRB activity. EIS identified the development of surface films including by an increase in its capacitive behavior that resulted in lower relative total impedance at a given low frequency (i.e. 100 mHz). Test results confirmed that SRB proliferation and corrosion can occur as the fouling macroorganism can accommodate different environmental condition.

Composite patch repair of damaged tubular members from flare boom structures subjected to compressive loads

Conventional repair method for steel structures requires cutting and welding processes, which in offshore platforms may impose several disadvantages. Composite material repair has become an alternative for the rehabilitation of damaged structures and has been widely applied in other industries. In this work a numerical-experimental investigation evidences the effectiveness of the composite patch repair for flare boom corroded tubular elements subjected to axial compressive loads. A finite element model developed to determine the minimum composite laminate thickness that recovers the structural element strength is validated through numerical simulations. Twelve API 5L grade B reduced scale steel tubes with central perforations and similar longitudinal and transverse slenderness, respectively defined by length to radius of gyration of the cross-section area and diameter to thickness ratios, are tested covering the range of interest for full scale members. The composite material consists of a hybrid fabric made of carbon and glass fibers impregnated with epoxy resin. Severe localized corrosion is considered conservatively, idealized as a circular perforation in half the element length. In many cases the maximum load of the repaired tube even exceeded the intact tube capacity. Moreover, it is shown that sufficient load capacity recovery is achieved for the conditions assumed.

Chandler-Loop surveyed blood compatibility and dynamic blood triggered degradation behavior of Zn-4Cu alloy and Zn

Zinc (Zn) and its alloys have been considered promising absorbable metals for medical implants. However, the dynamic interaction between Zn-based materials and human blood after implantation remains unclear. In this study, a modified Chandler-Loop system was applied to assess the blood compatibility and initial degradation behavior of a Zn–4.0Cu (wt%) alloy (Zn-4Cu) and Zn with human peripheral blood under circulation conditions. In this dynamic in vitro model, the Zn-4Cu and Zn showed sufficient blood compatibility. The numbers of erythrocytes, platelets, and leukocytes were not significantly altered, and appropriate activations of the coagulation and complement system were observed. Concerning initial degradation behavior, the product layers formed on the surfaces comprise a mixture of organic and inorganic compounds while the inorganic constituents decrease toward the outer surface. Considering the corrosion morphology and electrochemical behaviors, Zn-4Cu exhibited milder and more uniform degradation than Zn. Additionally, long-term degradation tests of 28 days in human peripheral blood, human serum, and Dulbecco's phosphate-buffered saline (DPBS) demonstrated that the Zn-4Cu showed relatively uniform degradation in blood and serum. On the contrary, in DPBS, severe localized corrosion appeared along the grain boundary of the secondary phase, which was likely attributed to the acceleration of galvanic corrosion. The Zn was found with localized corrosion impeded in the blood albeit with apparently developed deep pitting holes in the serum and DPBS.

Surface integrity analysis of electrochemical machining of γ-TiAl alloys

Surface integrity is directly related to component performance and service life. Various characteristics of the surface integrity of the three typical γ-TiAl alloys by electrochemical machining (ECM) were studied, including surface morphology, 3D profile, surface roughness, cross section, microhardness, residual stress and element analysis. Two current densities 5 and 50 A/cm2 were selected for comparative experiments. The results show that the three γ-TiAl alloys exhibit their own unique morphologies at low current density, and there is severe localized corrosion on the machined surface, resulting in the rough surface. However, the three γ-TiAl alloys show very smooth surfaces at high current density. This result also shows that the surface roughness values of the three γ-TiAl alloys all decrease gradually with the current density increasing, in which the extruded Ti-48Al-2Cr-2Nb has lowest surface roughness value (about Ra 0.506 μm) at 50 A/cm2. It is found that the microhardness of the machined surface of the three γ-TiAl alloys all decreased slightly, with a decrease of about 10 HV compared with the matrix. The residual stress of the samples decreases slightly after ECM, and the influence of different current density on the residual stress is not obvious. Finally, it is also proved that ECM has no effect on the elements of the machined surface.

Corrosion Behavior of 316L Stainless Steels Exposed to Salt Lake Atmosphere of Western China for 8 years

The evolution of corrosion behavior of 316L stainless steels exposed to salt lake atmosphere for 8 years was investigated. The results showed that the stainless steel in salt lake atmosphere had a greater corrosion rate during the initial exposure time and relatively lower corrosion rate during the subsequent exposure time. Dust depositions accumulated on the downward surface caused severe local corrosion of stainless steel. As exposure time prolonged, the relative amount of Croxide and Feoxide in the corrosion products gradually increased, which may directly affect the corrosion rate of stainless steels. Moreover, the maximum pit depth followed a power function with respect to exposure time.

Investigation of Corrosion Behavior of Drain Pipes of Process Compressors in Direct Reduction Unit.

Corrosion is a natural process in the destruction of industrial components. Corrosion can be intensified and finally led to destruction where there are temperature increase and microbial agents in addition to the main causes of corrosion. Process compressors were employed in order to meet the gas pressure and flow of the process in the direct reduction unit, and carbon steel pipes were used to separate water from the gas. However, these pipes are punctured and leak water and gas in less time in comparison with the other units. In order to examine the destruction reasons, several samples of the destructed pipe were provided, and they were studied by scanning electron microscopy (SEM) and EDS. The results showed that, besides regular agents like high temperature and acidic medium, microbial corrosion by sulfate-reducing bacteria and H2S gas effect lead to intensifying local and sub-sediment corrosion so that the component will be destructed in less time. The presence of FeS layer will result in severe local corrosion.

Corrosion behavior of Q235B carbon steel in simulated seawater pumped storage system under operational conditions

Seawater pumped storage systems have bright prospect for energy storage in the coming years. The operational conditions of seawater pumped storage system are complex and harsh, where metal materials suffer from severe general and local corrosion. The corrosion behavior of Q235B carbon steel in simulated seawater pumped storage system under operational conditions was studied by potentiodynamic polarization, cyclic potentiodynamic polarization, and scanning electron microscope (SEM). The results confirm that the working pressure affected the corrosion resistance of Q235B carbon steel during the whole immersion period. The pressure promoted the electrochemical reaction of corrosion process and the corrosion rate increased with pressure at the initial immersion period. However, the stable rust layer formed after longtime immersion at different pressures increased the corrosion resistance of carbon steel, and decreased the corrosion degree of carbon steel. Meanwhile, the working pressure affected the pitting corrosion behavior of Q235B carbon steel during the whole immersion period. The pitting corrosion potential was more negative and the tendency of pitting corrosion was higher at 4 MPa during the whole immersion period. However, pressure also accelerated the formation rate of protective rust layer on the steel surface. Q235B carbon steel has higher susceptibility to pitting corrosion at 4 MPa in the static seawater.

Mechanistic understanding of the corrosion behavior of Mg4Zn0.2Sn alloys: From the perspective view of microstructure

The corrosion behavior of as-cast and extruded Mg4Zn0.2Sn (wt.%) alloys was comprehensively compared in 0.5 wt.% NaCl solution. Microstructure and surface chemistry related corrosion performance has been revealed. Zinc-supersaturated solid solution is formed around the intermetallics in the as-cast alloy, but zinc alternately segregates between the α-Mg matrix in the extruded alloy. According to Scanning Kelvin Probe Force Microscopy and immersion tests, micro-galvanic corrosion between the precipitates (intermetallics or impurity particles) or Zinc-rich area and the matrix resulted in severe localized corrosion in both conditions. However, alternation of microstructure induced by extrusion significantly enhanced the corrosion resistance of Mg4Zn0.2Sn alloy.

Influence of cementite spheroidization on relieving the micro-galvanic effect of ferrite-pearlite steel in acidic chloride environment

The corrosion behavior of the as-received steel and the spheroidized steel in acidic chloride environment was investigated. The results indicate the corrosion mode and corrosion rate of two steels are diverse due to their difference in microstructure. For as-received steel with ferrite-pearlite microstructure, severe localized corrosion happens on the pearlite regions, and plenty of cathodic cementite remains in the pits, further strengthening the micro-galvanic effect and accelerating the corrosion rate. While for spheroidized steel with tempered martensite microstructure, the nanosized cementite particles evenly distributed on the ferrite substrate are easy to fall off, which can significantly reduce the cementite accumulation on the steel surface, relieving the acceleration effect of micro-galvanic corrosion.

A comparative study of corrosion behavior of an additively manufactured Al-6061 RAM2 with extruded Al-6061 T6

The corrosion behavior of additively manufactured (AM) Al-6061 RAM2 was compared with conventional extruded Al-6061 T6 within ten days of exposure in 0.5 M NaCl solution using electrochemical measurement and microscopic observations. At the beginning of exposure, the AM samples revealed superior corrosion performance compared to extruded counterparts. However, by increasing the time of exposure, the corrosion resistance of those samples decayed continuously. Incorporation of Ti-rich and B4C particles as the microstructure modifiers in the AM matrix reduced the integrity of the native oxide layer. It led to the cracking of the barrier film and severe localized corrosion.

Experimental and numerical studies on the electrochemical properties of an electrically assisted pressure joint of austenitic stainless steel and Ni-based superalloy

Electrochemical properties of an austenitic stainless steel and Ni-based superalloy dissimilar joint, produced by electrically assisted pressure joining (EAPJ), are investigated and compared to the base metals in a 3.5% NaCl solution at room temperature. The microstructural analysis reveals a sound joint without the presence of secondary phases and/or low melting phases (Laves) in the EAPJ joint due to the short diffusion time and rapid local heating. However, the microstructure of the joint is characterized by some degree of grain refinement, high dislocation densities, and a decrease in major passive-forming elements across the joint interface. These microstructural changes cause an increase in the risk of galvanic corrosion across the joint, with the SUS316L side undergoing severe localized corrosion attacks. Furthermore, a numerical model is established using the corrosion parameters from the experiment to simulate the electrochemical behavior of the joint in a neutral environment. The simulation results agree reasonably well with the experimental results in relation to the corrosion potentials, current densities, and the corresponding corrosion rates. Also, the model is capable of tracking the dissolution of the SUS316L side of the joint during the corrosion process for any period.

Effect of Jet Impingement Velocity and Angle on CO2 Erosion-Corrosion with and without Sand for API 5L-X65 Carbon Steel.

Most oil and gas production wells have plenty of corrosive species present along with solid particles. In such production environments, CO2 gas can dissolve in free phase water and form carbonic acid (H2CO3). This carbonic acid, along with fluid flow and with/without solid particles (sand or other entrained particles), can result in unpredictable severe localized CO2 corrosion and/or erosion–corrosion (EC). So, in this work, the CO2 EC performance of API 5L X-65 carbon steel, a commonly used material in many oil and gas piping infrastructure, was investigated. A recirculating flow loop was used to perform these studies at three different CO2 concentrations (pH values of 4.5, 5.0, and 5.5), two impingement velocities (8 and 16 m/s), three impingement angles (15°, 45°, and 90°), and with/without 2000 ppm sand particles for a duration of 3 h in 0.2 M NaCl solution at room temperature. Corrosion products were characterized using FE-SEM, EDS, and XRD. The CO2 EC rates were found to decrease with an increase in the pH value due to the increased availability of H+ ions. The highest CO2 erosion–corrosion rates were observed at a 45° impingement angle in the presence of solid particles under all conditions. It was also observed that a change in pH value influenced the morphology and corrosion resistance of the corrosion scales.

The study of under deposit corrosion of carbon steel in the flowback water during shale gas production

Serious under deposit corrosion could occur in the shale gas flowback water environment. In this work, under deposit corrosion of Q235 carbon steel in a simulated CO2/O2-containing shale gas flowback water was studied using wire beam electrode, potentiodynamic polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results show that there is a galvanic corrosion effect between the deposit-covered electrode and bare electrode. The polarity of the deposit-covered electrode and bare electrode is reversed at 3 h. Before 3 h immersion, deposit-covered electrode acts as cathode and bare electrode acts as anode. However, after 3 h immersion, deposit-covered electrode turns into anode while bare electrode converts into cathode. The obvious localized corrosion characteristics can be observed under deposit and the corrosion products mainly consist of Fe2O3, Fe3O4 and FeCO3. WBE can be used to in situ monitor the occurrence and development of local corrosion under deposit. The current maps of WBE show that severe local corrosion has occurred on the electrodes covered by deposit.

Friction stir processing of a cast manganese-aluminum bronze for improving corrosion and cavitation erosion resistances

A cast manganese-aluminum bronze (MAB) is subjected to friction stir processing (FSP), and the corrosion and cavitation erosion behaviors are studied. Results indicate that FSP breaks the large-sized κ phases into small particles and remarkably homogenizes and refines the α and β phases in the cast substrate. Therefore, the hardness is raised after FSP. A finer microstructure is obtained by the double-pass FSP. The FSP MABs exhibit higher electrochemical activity than the cast in 3.5 wt% NaCl solution, probably due to the residual stress induced by severe plastic deformation during FSP. However, after long-term immersion, severe localized corrosion occurs and results in the formation of large-size corrosion pits on the cast MAB. By contrast, the FSPed MABs undergoes relatively uniform corrosion and no noticeable pits are found on the double-pass FSPed MAB because of the homogenized microstructure and formation of homogeneous and protective corrosion product films. Under cavitation erosion in 3.5 wt% NaCl solution, the mass loss rate of the FSPed MABs is only half that of the cast. For the cast and FSPed MABs, cavitation transforms the corrosion potential towards a positive direction and raises the corrosion current density by nearly an order of magnitude, and the mechanical impact contributes largely to the cavitation erosion damage. For the cast MAB, severe cleavage fracture occurs at the coarse β phases and large cavities form on the eroded surface. However, the FSPed MABs are evenly and slightly eroded because of the homogeneous microstructure and increased hardness.

Sealing of anodized AA2099-T83 Al-Cu-Li alloy with layered double hydroxides for high corrosion resistance at reduced anodic film thickness

The structure and corrosion resistance of anodized AA2099-T83 Al-Cu-Li alloy after layered double hydroxides (LDH) sealing and hot water sealing (HWS) were studied using scanning electron microscopy (SEM), X-ray diffraction, electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSST). Particularly, the corrosion resistance of the LDH-based coating system with reduced anodic film thicknesses was compared with that of the normal HWS-based coating system. It was found that LDH could be formed over the surface and within the pores of the anodic film within 30 min. With other conditions the same, the LDH-sealed alloy passed 1000 h of NSST without evident localized corrosion, contrasting with the HWS alloy, which showed severe localized corrosion after NSST for 120 h. Further, when the anodic film thickness was reduced from 3.7 to 1.3 μm, the LDH-sealed alloy still showed much better corrosion resistance than the normal HWS alloy. This work clearly demonstrates that it is possible to obtain high corrosion resistance for the anodized AA2099-T83 Al-Cu-Li alloy at much reduced anodic film thickness.

Insights into the Electrochemical Corrosion Behavior and Mechanism of Electroless Ni-P Coating in the CO2/H2S/Cl− Environment

The electrochemical corrosion behavior of Ni-P coating in 3.5 wt% NaCl solution-containing CO2 and H2S was investigated using electrochemical methods and surface characterization techniques. The results show that the presence of H2S can enhance the CO2 corrosion of Ni-P coated carbon steel by affecting both anodic and cathodic processes. The adsorbed layer only exists in the very early stage of corrosion and barely improves the anticorrosion performance of the coating. The formation of corrosion products (NiO and Ni3S2) renders temporary protection during immersion, but the addition of H2S accelerates the diffusion process at the electrolyte/coating interface and promotes the electrolyte penetration through the coating, causing severe localized corrosion and coating disbondment. A corrosion model is proposed to illustrate the corrosion and degradation process of Ni-P coated steel in the CO2/H2S/Cl− environment.

Surface conditions for microcosm development and proliferation of SRB on steel with cathodic corrosion protection

Steel components used in civil infrastructure are susceptible to microbiologically influenced corrosion (MIC) in marine environments due to the interactions between the metal and its environment with varying water quality parameters (chemical and biological). Sulfate-reducing bacteria (SRB) has been associated with MIC by a cathodic depolarization mechanism due to the reaction of surface hydrogen. Recent findings at a Florida bridge showed severe localized corrosion associated with microbial activity and heavy marine fouling of the submerged steel piles. Cathodic protection can be applied to control the corrosion of steel; however, the mitigation may be impaired by the microbial activity and marine fouling. The objective of this work was to explore reduction reactions on cathodically polarized steel surfaces and evaluate the influence of cathodic polarization on sulfate reduction reaction. It was of interest to characterize the reduction reaction in crevices representative of different physical properties of the marine foulers where SRB can be supported. Field testing was conducted to differentiate the cathodic protection currents that develop in the presence of microorganisms under the layer of marine fouling in natural environments. Laboratory tests were conducted to elucidate the cathodic reactions by potentiostatic cathodic polarization of steel specimens in solutions inoculated with SRB. Field testing showed that proliferation of the bacteria was not inhibited in the presence of cathodic polarization at about −1000 mVCSE and corrosion continued in the localized regions under fouling encrustation. The larger cumulative charge relating to the apparent sulfate reduction by SRB corresponded to higher levels of cathodic polarization. Sulfate reduction by SRB can be a significant contributor to the electrochemical process for steel corrosion with cathodic polarization. For the porous crevice environments, large cathodic currents and high sulfate reduction coincided with the development of sustained SRB growth.

Self-accelerated corrosion of nuclear waste forms at material interfaces.

The US plan for high-level nuclear waste includes the immobilization of long-lived radionuclides in glass or ceramic waste forms in stainless-steel canisters for disposal in deep geological repositories. Here we report that, under simulated repository conditions, corrosion could be significantly accelerated at the interfaces of different barrier materials, which has not been considered in the current safety and performance assessment models. Severe localized corrosion was found at the interfaces between stainless steel and a model nuclear waste glass and between stainless steel and a ceramic waste form. The accelerated corrosion can be attributed to changes of solution chemistry and local acidity/alkalinity within a confined space, which significantly alter the corrosion of both the waste-form materials and the metallic canisters. The corrosion that is accelerated by the interface interaction between dissimilar materials could profoundly impact the service life of the nuclear waste packages, which, therefore, should be carefully considered when evaluating the performance of waste forms and their packages. Moreover, compatible barriers should be selected to further optimize the performance of the geological repository system.

In situ study of flow accelerated corrosion and its mitigation at different locations of a gradual contraction of N80 steel

A gradual pipe contraction may cause severe localized corrosion resulted from the flow acceleration, thus threating the operating safety of pipelines in the oil and gas field. Until now, the quantitative study on the correlation between local corrosion rate and local hydrodynamics at the gradual pipe contraction is still missing.In this work, the flow accelerated corrosion and its mitigation at different locations of a gradual pipe contraction of N80 steel are in situ investigated using computational fluid dynamics simulation and array electrode technique combined with electrochemical impedance spectroscopy. The results show that the distribution of corrosion rate at the gradual pipe contraction is in good accordance with the distribution of hydrodynamics parameters including flow velocity and wall shear stress, i.e., the higher flow velocity or higher wall shear stress is, the higher local corrosion rate is. The presence of an imidazoline derivative inhibitor can greatly mitigate the corrosion at the gradual pipe contraction through hindering the mass transfer process and charge transfer process of corrosion. Furthermore, in the presence of inhibitor the differences in corrosion rate among different locations at the gradual pipe contraction are also effectively reduced, or even disappeared at low flow velocity. Therefore, the addition of the inhibitor is an effective way to mitigate or even eliminate the flow accelerated corrosion at the gradual pipe contraction in the oil and gas field.