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.
Drillpipe failure is an outstanding issue in drilling engineering, often involving great financial losses. In view of the special features of the flow channel in the high failure zone, this article ...analyzes the drillpipe failure mechanism from the point of view of flow induced corrosion. Based on the Eulerian-Langrangian method and the discrete phase model, a numerical simulation method is used to investigate the flows of the drilling fluid in the drillpipe connector during the operation of three typical drilling methods (mud drilling, air drilling and foam drilling). From the flow field in the drillpipe connector, especially, the velocity and pressure distributions in the threaded nipple and the thickened intermediate belt, one may detect the existence of the flow induced corrosion. Then, some structural optimization measures for the drillpipe connector are proposed, and the optimization effects are compared.
For corrosion protective coatings that are designed to give lifetimes of protection that may extend to 50 years, valid accelerated test methods are necessary to develop improved systems and validate ...performance. Fluid flow over metals has long been believed to influence the corrosion process. Studies have been focused on the effects of flow rate on the corrosion of bare metals. The influence of fluid flow on the degradation of metal-protective coatings has received less attention. This paper describes a preliminary study on the influence of laminar flow on organic coatings. A Hele-Shaw cell and its associated fluid control apparatuses are incorporated into the electrochemical cell setup. The barrier properties of the coating as a function of immersion time and flow rate have been monitored by electrochemical impedance spectroscopy. We observe that the barrier properties of the coating measured electrochemically decrease exponentially with the increasing flow rate. We propose that the flowing electrolyte solution could be used in acceleration tests for the lifetime prediction of organic coatings as the acceleration of failure we have observed does not appear to change the mechanism of failure. Further analysis is proposed to validate immersion flow rate as a universal accelerating parameter for coating failure.
The treatment against flow induced localized corrosion phenomena (FILC) is generally performed by choosing materials of improved protective performances. The alternative solution, which consists in ...acting directly on the flow has only been considered in the recent years. The analysis presented here describes chemical actuators—polymer solutions and surfactant solutions—which are used to reduce the turbulent drag. Microscopic origin of the phenomenon is emphasized with resulting effect on large turbulent structures, which are thought to be responsible of FILC. From the knowledge of the main flow characteristics in drag-reducing conditions, a criterion for the onset of FILC has been expressed which shows a huge increase of the time required to see the appearance of the damage. The use of surfactant solutions instead of polymer solutions for practical applications is strongly suggested in view of the reversible degradation that undergo the thread-like micelles involved in the mechanism, whereas polymer coils are irreversibly degraded with a resulting loss of the Drag-Reduction effect.
The diffusion controlled corrosion of the base of agitated vessels with flat and conical bottom was studied using the diffusion controlled dissolution of copper in acidified dichromate technique. ...Variables studied were impeller rotation speed, inclination of the conical bottom, physical properties of the solution and the presence of drag reducing polymers. For the present case where four blade 45° pitched turbine impeller was used in a baffled agitated vessel, the rate of diffusion controlled corrosion of the flat bottom was given by the equation
Sh=0.586Sc
0.33Re
0.658
while for the conical bottom the data were correlated by the equation
Sh=0.204Sc
0.33Re
0.7(L/r)
−0.33.
Drag reducing polymers were found to inhibit diffusion controlled corrosion only in agitated vessels with flat bottom, they were found to have little effect on the rate of corrosion of conical bottoms.
A mechanistic approach is taken in a discussion of the control of flow-induced corrosion. An historical survey demonstrates the close interaction of theory and practice. There are a number of ...mechanisms of the conjoint action of flow and corrosion that result in four types of flow-induced corrosion:
1.
(1) mass transport controlled corrosion;
2.
(2) phase transport controlled corrosion;
3.
(3) erosion corrosion and
4.
(4) cavitation corrosion.
Prevention strategies are dependent on the type of mechanism concerned. A knowledge of hydromechanical conditions is a prerequisite for the proper design of equipment and a few basic rules have to be followed. In the field of materials selection there is an increasing trend towards choosing passivating materials. If the mechanical stability dominates, materials, such as cast alloys and duplex steels, are applied, especially in particle-containing liquids. Other protection methods, such as metallic, organic and ceramic coatings, inhibition and electrochemical protection, are discussed and it is shown that a number of highly interesting problems still await a solution.
The slurry erosion–corrosion behaviour of TiN coated
α-Ti alloy in aqueous silica slurry containing 3.5% NaCl has been investigated using a jet-in-slit rig. Erosion–corrosion tests were performed ...with slurry having jet velocity range 4.8–12.8 m s
−1 and at normal impact angle. Because of synergistic effects between erosive wear and flow-induced corrosion, the erosion–corrosion rates of the TiN coating and
α-Ti substrate were higher than the sum of erosive wear rates and flow-induced corrosion rates. At the lower slurry velocity, the TiN coating deposited on the
α-Ti substrate presented better slurry erosion–corrosion resistance. With increasing slurry velocity, however, perforating, cracking and fragmenting of the hard TiN coating occurred and the protection effect of the coating layer reduced with the erosion–corrosion duration. And then the volume loss of the
α-Ti substrate was enhanced through cracking of flakes induced by stress and corrosion.
When a flow enters a pipeline or goes over an obstacle, a new boundary layer is developed and produces a local corrosion rate that is greater than the average corrosion rate. Equations are developed ...to calculate this local flow-induced corrosion rate. The calculated local corrosion rate varies from a fraction of mm/year to 1.27 mm/year (50 mils/year), depending on the temperature, velocity, and location of the flow. The calculations also show that the maximum local corrosion rate occurs at a short distance from the edge of the pipe entrance. The wavy appearance of erosion-corrosion failure on metal surfaces can be explained by the boundary layer theory and the convective mass transfer of ferrous ions.
The effect of decaying Swirl flow on the rate of diffusion controlled corrosion of a pipe was studied by using the diffusion controlled dissolution of copper in acidified dichromate. Variables ...studied were flow rate, physical properties of the solution and length of the tube. The data were correlated by the equation
Sh=4.14
Sc
0.33
Re
0.56
L/d
−0.38.
The effect of polyox WSR-301 drag reducing polymer on the rate of diffusion controlled corrosion of the pipe was also studied, the polymer was found to decrease the rate of corrosion by an amount ranging from 3 to 26% depending on the operating conditions.
