Electrical Engineering

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A study of corrosion for high pressure, large diameter pipelines under horizontal and 2 degrees oil/water/gas multiphase flow conditions was carried out. The water cuts studied were 10%, 20% and 30% ASTM saltwater. A light oil with viscosity of 2 cP was used as the oil phase. Carbon dioxide was used in the gas phase. The predominant flow was found to be slug flow and all corrosion experiments were carried out in this regime. Finally, the resulting data was analyzed.

World University root node

(SoE) School of Engineering

Proceedings - SPE Annual Technical Conference and Exhibition

Study of sweet corrosion at low water cut in multiphase pipelines

Multiphase oil/water/gas flow regime transition studies are carried out in a 10-cm I.D., 18-m long Plexiglas pipe at inclinations of ±2° at system pressures up to 0.79 MPa. The results are compared to those of other researchers, and the effects of pressure, inclination and liquid viscosity are shown. The water cut of the liquid has some effects on the transitions from stratified to slug flow. Increasing the water cut results in the transition occurring at higher liquid velocity at the same gas velocity. Water cut has little effect on the slug/annular transition for the low viscosity oil used. The system pressure has a small effect on the transition from stratified to slug and slug to annular. For the transition from stratified to slug, increasing the system pressure, requires higher liquid velocity. The transition from slug to annular occurs at lower liquid velocity with increasing system pressures. The inclination of the pipe has an effect on the transition from slug to annular flow. Increasing the inclination causes the transition to occur at lower gas velocity at the same liquid velocity.

American Society of Mechanical Engineers, Petroleum Division (Publication) PD

Modeling flow regime transitions in large diameter inclined pipelines

This paper presents a new family of circuits for single phase diode bridge rectifiers capable of drawing approximately sinusoidal current at unity power factor with high efficiency and minimum voltage stress across the switches. They can work as either boost or flyback converters. The circuits consist of a single-phase diode bridge rectifier, followed by a boost stage containing two switches-the main switch for controlling the output DC voltage and the auxiliary for achieving zero voltage switching (ZVS). The switching frequency of the converters is maintained constant. The paper explains the principle of operation and describes the analysis of each mode of operation for both boost and flyback converters. It also gives design criteria, derived from the mathematical analysis carried out, for achieving ZVS under all loading conditions. The simulation results obtained using PSPICE demonstrate the validity of the proposed converters.

IEEE Region 10 Annual International Conference, Proceedings/TENCON

New fixed-frequency zero-voltage switched low-cost single phase high quality rectifier circuits with minimum voltage stress across the switches

The effect of drag-reducing agent (DRA) on multiphase flow in upward and downward inclined pipes has been studied. The effect of DRA on pressure drop and slug characteristics such as slug translational velocity, the height of the liquid film, slug frequency, and Froude number have been determined. Experiments were performed in 10-cm i.d., 18-m long plexiglass pipes at inclinations of 2 and 15 degfor 50 percent oil-50 percent water-gas. The DRA effect was examined for concentrations ranging from 0 to 50 ppm. Studies were done for superficial liquid velocities between 0.5 and 3 mJs and superficial gas velocities between 2 and 10 m/s. The results indicate that the DRA was effective in reducing the pressure drop for both upflow and downflow in inclined pipes. Pressure gradient reduction of up to 92 percent for stratified flow with a concentration of 50 ppm DRA was achieved in 2 deg downward inclined flow. The effectiveness of DRA for slug flow was 67 percent at a superficial liquid velocity of 0.5 m/s and superficial gas velocity of 2 m/s in 15 deg upward inclined pipes. Slug translational velocity does not change with DRA concentrations. The slug frequency decreases from 68 to 54 slugs/min at superficial liquid velocity of 1 m/s and superficial gas velocity of 4 m/s in 15 deg upward inclined pipes as the concentration of 50 ppm was added. The height of the liquid film decreased with the addition of DRA, which leads to an increase in Froude number. © 1999 by ASME.

Journal of Energy Resources Technology, Transactions of the ASME

Effect of drag-reducing agent on slug characteristics in multiphase flow in inclined pipes

This paper presents a family of circuits for single phase diode rectifiers capable of drawing approximately sinusoidal current waveforms at unity power factor with high efficiency and minimum voltage stress across the switches. Moreover, they are suitable to work as boost and flyback converters. These topologies use coupled inductors with capacitor for resonance to achieve zero voltage switching (ZVS) of the converters. The circuits consist of a single-phase diode bridge rectifier, followed by a boost stage containing two switches-the main switch for controlling the output DC voltage and the auxiliary switch for achieving ZVS. The output voltage is regulated by employing fixed frequency control. The paper explains the principle of operation and describes the analysis of each mode of operation for both boost and flyback converters. It also gives design criteria, derived from the mathematical analysis carried out, for achieving ZVS under all loading conditions from no load to full load. The simulation results obtained using PSPICE demonstrate the validity of the proposed converter.

IECON Proceedings (Industrial Electronics Conference)

Fixed-frequency zero-voltage switched low-cost single phase high quality rectifier circuits with minimum voltage stress across the switches

This paper presents some novel synchronized quasi-resonant circuits for achieving soft-switching DC/DC boost and flyback power converters. These topologies use coupled inductors with capacitor for resonating the circuit to achieve zero voltage switching of the power converters. The circuits have minimum voltage stress across the switches. Moreover, they have reduced commutation losses and increased switching frequency. The paper explains the principle of operation of the circuit and describes the analysis of each mode of operation for both boost as well as flyback power converters. It also gives design criteria, derived from the mathematical analysis carried out, for achieving zero voltage switching under all loading conditions from no load to full load. The feasibility of the proposed circuits has been verified by PSPICE simulation. © 1998 IEEE.

PESC Record - IEEE Annual Power Electronics Specialists Conference

Certain novel synchronized quasi-resonant topologies for achieving soft-switching DC/DC boost and flyback converters with minimum voltage stress across the switches

A non-contact, non-destructive technique for the depth profiling of micromachined structures is presented. Based on the mirage or optical-beam deflection method of photothermal spectroscopy, an experimental measurement of a 8 μm step in silicon is given by way of illustration. © 1998 Elsevier Science S.A.

Sensors and Actuators, A: Physical

Mirage-effect-based depth profiling of micromachined silicon structures

This paper summarizes the results of mass transfer mechanisms under disturbed liquid-gas flow in 10 cm diameter pipe using electrochemical limiting current density and potentiostatic noise technique. The solution used is potassium ferro/ferricyanide dissolve in 1.3 N sodium hydroxide system. Mass transfer coefficients in full pipe flow and slug flow are obtained. The relationship between mass transfer coefficient with full pipe flow velocities and with slug flow Froude numbers are studied. The impact of bubbles in slugs on the mass transfer coefficient is revealed. The impact of flow disturbance, including weld beads and pits, are discussed for both full pipe flow and slug flow. © 1998 by NACE International.

NACE - International Corrosion Conference Series

Calculation of mass transfer in multiphase flow

Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of gas bubbles (Gopal et al, 1997). Corrosion rate measurements have been made at pressures up to 0.79 MPa and temperatures up to 90°C, and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude number. This paper describes mass transfer measurements under multiphase slug and annular flows using the limiting current density technique. The experimentsare carried out in a 10-cm-dia pipe using a 0.01-Mpotassium ferro/ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6, and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The remits show instantaneous peaks in the mass transfer rates corresponding to the pulses of bubbles in slug flow. Instantaneous increases of 10-100 times the average values in multiphase flow are seen. Peaks are also seen in instantaneous mass transfer rates in some annular flows. © 1998 by ASME.

Multiphase flow-enhanced corrosion mechanisms in horizontal pipelines

A mechanistic model was developed for predicting carbon dioxide corrosion rates of carbon steel pipes in multiphase flow conditions. The model incorporates the chemistry, thermodynamics of carbon dioxide dissolution, multiphase mass transfer, electrochemical kinetics on the metal surface and the presence of a corrosion product film. The predicted corrosion rates show good agreement with the experimental results. © 1998 by NACE International.