In this work, an annulus-type recirculated batch reactor is designed to study the influence of different process parameters on the corrosion rate of metals under diffusion-controlled conditions. The ...effect of solution flow rate (for both laminar and turbulent flow regimes), physical properties of the solution, annulus geometrical parameters, and the effect of adding benzotriazole inhibitor on the corrosion are investigated. The rate of corrosion was expressed in terms of the mass transfer coefficient in the form of an empirical dimensionless correlation. The maximum attained efficiency of inhibition is 98% in the case of laminar flow and 90% in the case of turbulent flow conditions. The importance of the present work with its practical application for the corrosion and protection of double pipe heat exchangers and condensers where the flow is developing was highlighted.
In order to study the electrochemical corrosion law for the 13Cr stainless-steel tubing material in a high-speed Cl-containing liquid, a high-speed-flow experiment and a small three-electrode system, ...embedded in a small pipe, were used. The open circuit potential (OCP), polarization curve (PC) and electrochemical impedance spectroscopy (EIS) of the stainless-steel surface were tested in a medium with a flow velocity ranging from 10 to 22 m/s containing 1 w/% and 2 w/% of NaCl. By comparing it with the changes in the electrochemical-reaction parameters of the material in distilled water, the results of the experiment including the critical flow velocity, the change of corrosion rate and the electrochemical-reaction control steps were obtained. By theoretically solving the frictional force of the liquid against the wall surface and the adsorption capacity of the oxide film, and assuming that the oxide film is a macromolecular combination, the relationship between the adsorption capacity of different surface films and the critical flow velocity in the high-speed pipe flow was established. The results of this experiment and calculation can provide a preliminary prediction of the critical flow velocity corresponding to the inflection point of the wall-surface corrosion rate in an industrial pipe flow, thereby improving the process parameters and reducing the wall damage.
Computational fluid dynamics (CFD) simulations are conducted using the volume-of-fluid (VOF) method to investigate the hydrodynamic characteristics of slug flow and the mechanism of slug flow induced ...CO
2 corrosion. The hydrodynamic characteristics are significantly affected by the viscous, interfacial, and inertial forces. In inertia dominated flows, the velocity of fully developed falling liquid film is increased with increased Taylor bubble rising velocity. The developing falling liquid film is formed at about the length of 0.5 diameter from the Taylor bubble nose, the fully developed falling liquid film is reached at about the length of 1.5–2.1 diameter from the Taylor bubble nose. The average mass transfer coefficient in the falling liquid film is always higher than that in the Taylor bubble wake zone. The iron ion near wall mass transfer coefficient is higher than that of hydrogen ion. The wall shear stress is increased with increased Taylor bubble rising velocity in fully developed falling liquid film zone, and the wall shear stress has a large fluctuation due to the chaotic and turbulent vortexes in Taylor bubble wake zone. The formation and the damage mechanism of the corrosion product scale are proposed for the gas–liquid two-phase vertical upward slug flow induced CO
2 corrosion. It is found that the wall shear stress of upward gas–liquid slug flow is alternate with high frequency, which is the key factor resulting in the corrosion product scale fatigue cracking. The CFD simulation results are in satisfactory agreement with previous experimental data and models available in literature.
Hydrodynamic and electrochemical noise measurements (ENMs), of AISI 304L stainless steel, were made in a pipe test section of 28
mm inside diameter for a range of flow regimes from laminar to ...turbulent. Mean flow velocities through the test section were controlled at 0.04, 0.07, 0.11, 0.36, 1.8 and 2.7
m
s
−1, equivalent to Reynolds numbers of 1000, 2000, 3000, 10
000, 50
000 and 75
000, respectively. Standard hydrodynamic parameters were employed to characterise and evaluate the complex interrelationship between the mass transfer rate of oxygen and momentum transfer through turbulence to the metal/solution interface. For AISI 304L stainless steel, pitting typically occurs in the form of metastable pits which either repassivated before achieving stability or grow to become stable pits. Metastable pitting was evident under all flow regimes. The fluid flow, whether laminar or turbulent, had little overall effect on the nucleation rates of metastable pitting events. Conversely, stable pit growth was most evident during laminar flow immediately before the transition to turbulent flow and close to the critical velocity (∼1.5
m
s
−1).
In order to find out the effect of fluid flow velocity on electrochemical reaction, the electrochemical parameters of super 13Cr stainless steel in 3.5% NaCl aqueous solution were measured by a jet ...flow system at different flow velocities. The electrochemical characters such as open-circuit potential and polarization curve were monitored online using a three-electrode electrochemical system. The results show that the increase in wall shear stress caused by the high flow velocity leads to the rupture of passive films and the exposure of fresh metal in the corrosive media, which cause the increase in corrosion rate. Meanwhile, the corrosion rate shows a significant growth when the flow velocity is less than 0–10.0 m/s. But it gradually decreases after reaching a maximum value.
The corrosion behavior of J55 carbon steel pipe was investigated in a water production well environment in the Athabasca oil sands reservoir. The corrosion morphologies and the chemical compositions ...of corrosion products were examined by surface analysis techniques. The protection performance of the formed corrosion scales was evaluated using electrochemical measurements. The results show that severe erosion corrosion occurs on the inner wall of the pipe and causes a significant thinning, which is the dominant reason for the pipe failure. Likewise, the failure of the thread zone is originated from the severe corrosion of inner wall as well. Localized corrosion of carbon steel occurs in the welding zone because of the galvanic effect between stainless steel and carbon steel. Furthermore, the distributions of corrosion products on the inner wall are notably affected by the flow. Dense and thick Ca-containing corrosion scales act as a physical barrier layer and prevent the steel from further corrosion, whereas localized corrosion occurs in the regions with loose and thin corrosion scales.
•The corrosion behavior of carbon steel pipes was studied after real service.•Severe flow-induced corrosion on the inner wall dominates the pipe failure.•The inner and outer walls undergo completely different corrosion processes.•The thick Ca-containing corrosion scales prevent the steel from further corrosion.•A corrosion model is proposed to interpret the corrosion process on the inner wall.
In this work, we present a numerical study to investigate the hydrodynamic characteristics of slug flow and the mechanism of slug flow induced CO
2 corrosion with and without dispersed small bubbles. ...The simulations are performed using the coupled model put forward by the authors in previous paper, which can deal with the multiphase flow with the gas–liquid interfaces of different length scales. A quasi slug flow, where two hypotheses are imposed, is built to approximate real slug flow. In the region ahead of the Taylor bubble and the liquid film region, the presence of dispersed small bubbles has less impacts on velocity field, because there are no non-regular intensive disturbance forces or centrifugal forces breaking the balance of the liquid and the dispersed small bubbles. In the liquid slug region, the strong centrifugal forces generated by the recirculation below the Taylor bubble lead to the effect of heterogeneity, which makes the profile of the radial liquid velocity component sharper with higher volume fraction of dispersed small bubbles. The volume fraction has a maximum value in the range of
r/
R
=
0.5–0.6. Meanwhile, it is usually higher than 0.35, which means that larger dispersed bubbles can be formed by coalescences in this region. These calculated results are in good agreement with experimental results. The wall shear stress and the mass transfer coefficient with dispersed small bubbles are higher than those without dispersed small bubbles due to enhanced fluctuations. For short Taylor bubble length, the average mass transfer coefficient is increased when the gas or liquid superficial velocity is increased. However, there may be an inflection point at low mixture superficial velocities. For the slug with dispersed small bubbles, the product scales still cannot be damaged directly despite higher wall shear stress. In fact, the alternate wall shear stress and the pressure fluctuations perpendicular to the pipe wall with high frequency are the main cause for breaking the product scales.
To clarify the impacts of the hydrodynamic boundary layer and the diffusion boundary layer in the near wall zone on gas–liquid two-phase flow induced corrosion in pipelines, the hydrodynamic ...characteristics of fully developed gas–liquid slug flow in an upward tube are investigated with limiting diffusion current probes, conductivity probes and digital high-speed video system. The Taylor bubble and the falling liquid film characteristics are studied, the effects of various factors are examined, and the experimental results are compared with the data and models available in literature. The length of Taylor bubble, the local void fraction of the slug unit and the liquid slug, the shear stress and mass transfer coefficient in the near wall zone, are all increased with the increase of superficial gas velocity and decreased with the increase of superficial liquid velocity, whereas the length of liquid slug and the liquid slug frequency are changed contrarily. The alternate wall shear stress due to upward gas–liquid slug flow is considered to be one of the major causes for the corrosion production film fatigue cracking. A normalized formula for mass transfer coefficient is obtained based on the experimental data.
In order to relate a shear stress controlled-corrosion at the impinged jet wall to that in a pipe the pressure drop along a jet tube and the mass transfer rate at eight locations on the jet-impinged ...wall were measured concurrently using microelectrodes. The shear stress on the impinged jet wall increased radially giving stagnation and jet wall regions in the order of 2 and 2.9 times the jet radius, respectively. The mean of the jet-impinged wall shear stresses at all radial positions was 50–120 times that at the pipe wall at any given
Re. A factor of about 80 may be used where the jet impinged wall corrosion rates are to be used to estimate corrosion in pipe flow at the same
Re.
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