Analysis of the Erosion-Corrosion Mechanism of the Air Cooler in a Hydrocracking Unit:A Numerical and Experimental Study

Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.

Effect of Aging Temperature on Erosion-Corrosion Behavior of 17-4PH Stainless Steels in Dilute Sulphuric Acid Slurry

The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope （SEM）. The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows： pure erosion （wear） was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.

Numerical Simulation of Erosion-Corrosion in the Liquid-Solid Two-Phase Flow

Erosion-corrosion of liquid-solid two-phase flow occurring in a pipe with sudden expansion in cross-section is numerically simulated in this paper. The global model for erosion-corrosion process includes three main components: the liquid-solid two-phase flow model, erosion model and corrosion model. The Eulerian-Lagrangian approach is used to simulate liquid-solid two-phase flow, while the stochastic trajectory model was adopted to obtain properties of particle phase. Two-way coupling effect between the fluid and the particle phase is considered in the model. The accuracy of the models is tested by the data in the reference. The comparison shows that the model is basically correct and feasible.

Erosion-corrosion behavior of Pd-Co and Pd-Cu films on 316L stainless steel in simulated PTA slurry environment

Pd-Co films with the Co content varying from 21.9% to 34.62%（mole fraction） and Pd-Cu（5% Cu, mole fraction） film were electrodeposited on 316 L stainless steel, and the erosion-corrosion resistance of the Pd-Co and Pd-Cu plated samples in a simulated boiling pure terephthalic acid（PTA） slurry environment was studied with methods of mass loss test, polarization measurement and scanning electron microscopy（SEM）. Under the static state condition, both the Pd-Cu and Pd-Co plated samples exhibit good corrosion resistance and the Pd-Cu film behaves slightly better. However, with increasing the stirring speed, the corrosion rate of the Pd-Cu plated samples increases obviously while that of the Pd-Co plated samples shows only slight increase. Higher microhardness and lower surface roughness of Pd-Co film than those of Pd-Cu film, as well as good corrosion resistance, may be the main reasons for better erosion-corrosion resistance in the strong reductive acid plus erosion environment.

Investigation of erosion-corrosion behavior of Q235B steel in liquid-solid flows

This work aims to investigate the erosion-corrosion behavior of Q235B steel in liquid-solid two-phase flows.The weight loss rate,surface morphology and electrochemical parameters of Q235B steel at different temperatures(20℃,30℃,40℃)and flow velocities(6 m/s,7 m/s,8 m/s,9 m/s,10 m/s)were studied separately.The results show that the weight loss rate of Q235B steel specimens after erosion-corrosion increases with increasing flow velocity and temperature.For the erosion-corrosion process,the corrosion rates of specimens increase with increasing flow velocity.The results of surface morphology show that the circular pits with clear edges are distributed randomly over specimen surface at low flow velocity,but the pit edge becomes vague at high flow velocity.With temperature increasing,the erosion-corrosion damage became serious as shown by the aggregation of large and small pits on specimen surface.The working mechanism of erosion-corrosion is found to vary with flow velocity and temperature.The relationships among erosion-corrosion components are quantitatively represented and show that synergy dominates the progress of material loss.Corrosion enhances erosion that is a dominant component in the synergy.The inactions of erosion-corrosion can be described by"synergistic"and"additive"behavior.The results show that"additive"effect becomes more significant with increasing flow velocity but decreases with increasing temperature,while"synergistic"effect is not sensitive to flow velocity and temperature.

Microstructures and erosion-corrosion behavior of Fe-B alloy containing chromium and nickel

The Fe-B alloy containing chromium and nickel was prepared, and the microstructure and erosioncorrosion behavior of the alloy were investigated by means of scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction analysis, Leica digital image analysis, a hardness tester and an erosioncorrosion tester. Cr28 white cast iron was used for comparison. Results show that the microstructures of both as-cast and heat-treated Fe-B alloys consist of austenite and borocarbide. The nickel and chromium elements are mainly distributed over the matrix and borocarbide, respectively. The hardness of the austenite matrix and the Rockwell hardness of heat-treated Fe-B alloy are higher than those of as-cast Fe-B alloy. In the erosioncorrosion test of the slurry, the erosion-corrosion weight loss of Fe-B alloy is lower than that of Cr28 white cast iron, indicating the Fe-B alloy displays higher erosion-corrosion resistance.

Erosion-corrosion and its mitigation on the internal surface of the expansion segment of N80 steel tube

We investigated erosion-corrosion(E-C) and its mitigation on the internal surface of the expansion segment of N80 steel tube in a loop system using array electrode technique, weight-loss measurement, computational-fluid-dynamics simulation, and surface characterization techniques.The results show that high E-C rates can occur at locations where there is a high flow velocity and/or a strong impact from sand particles, which results in different E-C rates at various locations.Consequently, it can be expected that localized corrosion often occurs in such segments.The E-C rate at each location in the expansion segment can be significantly mitigated with an imidazoline derivative inhibitor, as the resulting inhibitor layer significantly impedes the electrochemical reaction rate.However, we found that this inhibitor layer could not effectively reduce the difference in the erosion rates at different locations on the internal surface of the expansion segment.This means that localized corrosion can still occur at the expansion segment despite the presence of the inhibitor.

Erosion-corrosion investigation of high chromium cast irons using newly designed jet type tester

A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet velocity and attack angle can be accurately controlled. The repeatability and ranking consistency of the test results are satisfactory. The test parameters can be adjusted in a wide range, so that the tester can simulate various practical working conditions. Electrochemical test data can be automatically collected and processed. Dynamic polarization curves can be obtained during erosion-corrosion test, which can be used to study the dynamic corrosion characteristics.Two high chromium cast irons were studied in hot concentrated alkaline slurry. The results show that the erosioncorrosion mass loss rate and dynamic corrosion rate of 295Cr26 iron is lower than that of 185Cr13 under the conditions similar to alumyte processing. The mechanism of erosion-corrosion of 295Cr26 and 185Cr13 was studied by using the tester. The interaction between erosion and corrosion was also quantitatively evaluated.

Effect of nitrogen addition on microstructure and erosion-corrosion behavior of stainless steel in acidic slurry

Effect of nitrogen content on the microstructure and erosion-corrosion (E-C) behavior of stainless steel (containing about 25% Cr, 5%-6% Ni, and 1%-2% Mo) was investigated by using optical microscope(OM), potentiodynamic polarization curve and immersion method, a self-made rotating disk apparatus and scanning electron microscopy (SEM) and so on. The results show that with the increase of nitrogen content from 0 (no adding) to 0.485 wt.%, the Cr(eq)/Ni(eq) ratio of the tested materials decreases from 4.14 to 1.23 and the ferrite volume percentage of the steel tested linearly decreases approximately from 90% to 10%. The effect of nitrogen content on polarization behavior of the studied steel was not significant. All the passive current densities (I(p)) and pure corrosion rates (V(c)) of the different N content specimens in the acidic solution (slurry containing 0.1 M H(2)SO(4)+0.06% Cl(-)+0.4% F(-), the simplified zinc hydrometallurgy slurry) are too low and nearly negligible. Whereas the pure erosion rates (V(e)) of the four scenarios of the steels tested (N content, wt.%: N1, no adding; N2, 0.143%; N3, 0.289%; N4, 0485%, respectively) are much higher than their V(c) values. The V(e) values of the tested steels are in the order of N4 > N1 > N3 > N2, at the same time, the total weight loss rates (V(t)) follow the order of N4 > N1 > N3 > N2, too. N2 steel consisting of approximately equal volume fractions of ferrite (alpha) and austenite (gamma) exhibits the most excellent E-C resistance and erosion resistance, while the stainless steels possessing the big difference between alpha phase and gamma phase, such as N1 steel nearly possessing single ferrite or N4 steel nearly possessing single austenite, show poorer E-C resistance and erosion resistance.

Measurement and analysis of polarization curves of mild steel in sodium carbonate/bicarbonate solution under erosion-corrosion conditions

The polarization curves of mild steel in de-aerated 0.5 mol NaHCO 3+0.5 mol Na 2CO 3 solution with and without erodent particles of 300 g/L of 100 μm alumina have been measured using a rotating cylinder electrode (RCE) apparatus over the range of rotation speeds from 0 to 4 000 r/min. The results show that the mild steel in the de-aerated slurry exhibits classical active/passive polarization behavior. The speed of cylinder rotation has a great effect in the presence of particles on the active dissolution current density. The erosion-corrosion process is severely erosion-dominated for the mild steel. However, the poor corrosion resistance of the mild steel in such turbulent slurries is also significant, especially at lower than 4 m/s.

Comparison and Analysis of Erosion-Corrosion Test Apparatus IJR and RCE

The test apparatus used for investigating erosion-corrosion in aqueous media, including the pipe flow loop, impinging jet, rotating disk and rotating cylinder rigs is reviewed. With combining the impinging jet rig and rotating cylinder electrode rig, the hydrodynamic characteristics of both rigs are analysed.

STUDY ON THE EROSION-CORROSION BEHAVIOR OF STEELS AND THERMAL SPRAYED COATINGS

16Mn steel, 1Cr18Ni9 stainless steel, thermal sprayed Al2O3-TiO2 ceramic coating and nylon1010-5 %Al2O3 coating were tested with an erosion -corrosion tester.The effects of pH values and slurry velocities on the erosion-corrosion behavior of the materials tested were determined. The erosion-corrosion behavior of the materials tested changes with pH values and presents different change tendencies. The erosion-corrosion rates of the materials are increased with slurry velocities. The erosion-corrosion mechanisms for the steels and the coatings are considerably different.

Correlation between depassivation and repassivation processes determined by single particle impingement:Its crucial role in the phenomenon of critical flow velocity for erosion-corrosion

The correlation between depassivation and repassivation processes,which is significant in erosioncorrosion,was quantitatively investigated by single particle impingement tests at various flow velocities and impact angles.The results show that both repassivation and depassivation processes are associated with the kinetic energy of solid particle,and demonstrate that the repassivation is retarded by depassivation.This phenomenon probably results from the depassivation-induced microstructure evolution.On this basis,the dependence of critical flow velocity(CFV)for erosion-corrosion on the solid particle concentration and diameter is further theoretically predicted and experimentally verified.Accordingly,the crucial role of depassivation-repassivation in CFV phenomenon is further highlighted.

Erosion-corrosion resistance of Mo-Ti- and Ni-Cr-Mo-alloyed medium-carbon martensitic steels: a critical analysis of synergistic effect of erosion and corrosion

Grain refinement renders Mo-Ti-alloyed medium-carbon martensitic steel to exhibit high hardness,high strength,and good toughness,but the erosion-corrosion resistance of steel in a corrosive slurry environment is not known.Mo-Ti-alloyed medium-carbon martensitic steel is compared with Ni-Cr-Mo-alloyed medium-carbon martensitic steel,and the erosion-corrosion resistance of those two steels under impingement by NaCl solution with gravels has been investigated.Three components,pure-corrosion rate,pure-erosion rate,and synergistic effect of erosion and corrosion(SEEC)of erosion-corrosion rate,were quantified.The pure-corrosion and pure-erosion rates of Mo-Ti-alloyed steel were higher than those of Ni-Cr-Mo-alloyed one;however,its erosion-corrosion rate was relatively lower because of a weak SEEC.Surface plastic deformation and work hardening due to gravel impingement were the essential reason for SEEC,which could be reduced by grain refinement,and consequently,Mo-Ti-alloyed steel with finer grains had better erosion-corrosion resistance.Grain refinement could be an effective way to improve the erosion-corrosion resistance of martensitic steels.

Erosion corrosion control of 6061 aluminum alloy in multi-phase jet impingement conditions with eco-friendly green inhibitor

Erosion corrosion performance of 6061 aluminum alloy in simulated sea water slurry was investigated under multi-phase jet impingement conditions. The main objective of the work is to study erosion–corrosion of a material with engineering application and mitigate it using eco-friendly green inhibitor. Experiments were performed with the sand concentration of 0.3% and 0.3 μm size. The effect of temperature and flow rate on the performance of inhibitor was explored. Electrochemical methods were adopted for erosion-corrosion measurements. Experiments revealed that starch could mitigate erosion-corrosion with a maximum reduction efficiency of 58% at temperature of 303 K and flow rate of 4 L·min–1. Inhibition efficiency decreased with increase in flowrate and temperature. EIS spectrum demonstrated that the corrosion process in the presence on inhibitor was both charge transfer and mass transfer controlled. A key role of hydrodynamics in the performance of corrosion inhibitor was confirmed by the present study.

2D Materials as Protective Coating against Low and Middle Temperature (100°C - 300°C) Corrosion-Erosion in Waste to Energy Plant: Case of Graphene

The combustion of MSW contains several species which if liberated into the flue gas will participate in erosion-corrosion reactions with the alloy surface and with the oxide layers. Actually with the evolution of material science and the discovery of 2D materials, we can handle that situation as well as possible. The graphene as 2D material presents a lot of advantage due to it physical properties such: melting point, boiling point and thermal conductivity, which can help to manage the problem of low and middle temperature (100°C - 300°C) erosion-corrosion into the boiler wall of waste to energy. The aim of the study was focused on analyzing the resistance at low and middle temperature (100°C - 300°C) in the enclosed environment and the corrosion-erosion resistance abilities of the graphene sheet as the 2D protective coating material. This paper analyzed the possibility of using the graphene in the aggressive environment which is waste to energy boiler. The results obtained from this study after simulation using ANSYS software which is one of the best software for simulations showed that Graphene protects the furnace walls against corrosion-erosion for temperatures lower than 400°C and that in the presence of certain impurities such as: sodium (Na), sulfur (S), chloride (Cl) and Phos- phorous (P), Sodium Chloride (NaCl), Hydrogen Chloride (HCl), Dioxide of Carbone (CO2) and Dioxide of Sulfur (SO2).

Evolution of the Corrosion Product Film and Its Effect on the Erosion–Corrosion Behavior of Two Commercial 90Cu–10Ni Tubes in Seawater

The composition and structural evolution of the corrosion product film of two commercial 90Cu-10Ni tubes, namely TubeA and Tube B, after being immersed in natural seawater for 1, 3, and 6 months were characterized by scanning electronmicroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and its effecton the erosion--corrosion behavior of the tubes was determined through a rotating cylinder electrode system using variouselectrochemical techniques. For the freshly polished samples used as contrast samples, the flow velocity mainly enhancedthe cathodic reaction at low flow velocities while both the anodic and the cathodic reactions were remarkably accelerated athigher flow velocities. The corrosion product films formed on the two commercial 90Cu-10Ni tubes after being immersedin seawater for up to 6 months are of a complex three-layer or multilayer structure. The structural evolution of the films isout of sync for the two tubes. A continuous residual substrate layer depleted of Ni was observed in the inner layer of thefilms on Tube B after 30, 90, and 180 days＇ immersion, while it was observed in the film on Tube A only after 180 days＇immersion. The nature of the inner layer plays a crucial role in the erosion-corrosion resistance of the 90Cu-10Ni tubes athigher flow velocity. The film with a compact and continuous inner layer of Cu20 doped with Ni2＋ and Ni3＋ which bondsfirmly with the substrate could survive and even get repaired with the increased flow velocity. The film on Tube Bpossessing a hollow and discontinuous inner layer composed of the residual substrate was degraded rapidly with increasingrotation speed in spite of its quite good resistance at the stagnant or lower speed conditions.