Multiphase Technology, Inc. was formed in 1997 to provide:
- Test equipment for multiphase studies
- Corrosion and metallurgy training courses
Multiphase Flow Loop
Both laboratory and pilot plant scale multiphase (oil, water, and gas) flow loops
are available. These can be produced for conditions from ambient temperature and
pressure using plastic or stainless steel components, to high temperature, high
pressure, H2S testing in fully pressurized Hastelloy C-276 components.
Systems employ proprietary instrumentation for flow characterizations and corrosion
rate measurements. Facilities for undesirable reactions are available to compare
the effects of up-flow and down-flow. A typical system is shown schematically
in the following page.
Training Courses
Multiphase Technology, Inc. offers training courses in corrosion and metallurgy.
Typical course topics include:
- Basic Metallurgy
- Basic Corrosion
- Materials Section
- Fabrication Techniques
- QA/QC
- Specification Writing
- Design
- Corrosion Protection
- Corrosion Monitoring
- Corrosion Testing
- Non-Metallic Technology
- Water/Scale
- Failure Modes
- Case Histories
Courses are presented internationally by world renowned experts, and include fully setup protocol workbooks with samples problems.
For additional information, contact:
Multiphase Technology,
Inc.
12071 Fowlers Mill Road
Chardon, Ohio 44094
Phone: 440-942-1235
Fax: 440-942-0327
Introduction on Multiphase Flow
Multiphase flow designates
the transport of oil/water/gas in pipelines. In horizontal pipelines, the different
flow patterns that could be observed are given in the following figures. The flow
pattern will depend mainly on the gas and liquid velocities, and gas/liquid ratio.
For very high liquid velocities and low gas/liquid ratios, the dispersed bubble
flow (regime 1) is observed. For low flow rates of liquid and gas, a smooth or
wavy stratified flow (regimes 2 and 3) is expected. For intermediate liquid velocities,
rolling waves of liquids (regime 4) are formed. The rolling waves increase to
the point of forming a plug flow (regime 5) and a slug flow (regimes 6 and 7).
For very high gas velocities, the annular flow (regime 8) is observed.
Slug flow creates a tremendous turbulence at the front of the slug. At the slug front, gas bubbles are entrained in the liquid. They impact and collapse on the pipe wall, resulting in instantaneous high shear. Therefore, slug flow generates a very high shear stress at the pipe wall. General trends showed that corrosion rates increase with liquid velocity and hence shear stress.
Thus, corrosion conditions are very different under the various flow patterns. When corrosion protection is evaluated, the types of flow that exist in multiphase pipelines must be taken into account.
Factors Affecting the Corrosion
Rates
In oil and gas production,
the factors determining the corrosion conditions include temperature, pressure,
chemical compositions of the fluids, state of metal surface, flow rates, and flow
regimes. While it is relatively easy to reproduce temperature, pressure or chemistry
of the fluids in laboratory tests, other parameters are more difficult to simulate,
like the exact nature of the flow and the intermittent fluctuations in the flow.
Moreover, the overall behavior of corrosion inhibitors in the field is related to different characteristics. The performances of these chemicals depend on the corrosion inhibitor efficiency, the partitioning, foaming and emulsion properties, and the interactions with other chemicals.
In laboratory tests, the different autoclaves provide good initial screenings of corrosion inhibitors but only a multiphase flow loop reproduces the field corrosion conditions.
Corrosion Inhibition of Pipelines
Carrying High-Velocity Gas and Liquids
The main purpose of large
diameter flow loops for corrosion studies is to simulate the real corrosion conditions
encountered in multiphase pipelines. The flow loop reproduces:
- physical and chemical properties of the multiphase system (water/oil/gas), i.e. solution corrosivity;
- dynamic nature of the fluid flow, i.e. flow regime;
- kinetic shear forces on the pipe wall, which directly affect the corrosion rate observed at the pipe wall.
For oil and gas production, corrosion studies under high flow rate require the use of a sophisticated multiphase flow simulator, since high gas and liquid velocities must be reproduced simultaneously.
Schematic Diagram of a Multiphase Loop Facility
Typical Specifications of Flow Loops
Typical specifications of
existing flow loop systems are indicated below. Other specifications can be provided
according to the specified system. Please contact Cortest engineers for further
information.
- Materials:
plexiglas
stainless steel
Hastelloy
A flow loop in Plexiglas pipeline allows visualization of the flow patterns. Flow loops can be composed of single-phase, oil/water or CO2 gas/liquid phase systems. Flow loops in stainless steel, and Hastelloy for CO2-H2 S/liquid systems are also available.
- Pipe Diameter:
typically 4" (10 cm)
- Pressure:
Low pressure loop: 50 psi (3.5 bars)
High pressure loop: 1500 psi (100 bars)
- Temperature:
Low pressure loop: 10 — 60°C
High pressure loop: 10 — 130°C
- Flow Rate:
Gas velocities: 0 — 20 m/s
Liquid velocities: 0 — 4 m/s
Instrumentation
- Corrosion Monitoring:
Corrosion coupons
High-sensitivity probes
Linear Polarization Resistance (LPR) probes
Electrochemical Impedance Spectroscopy (EIS) probes
Electrochemical Noise (ECN) probes
- Flow Visualization:
Video camera
Video recorder
Multiphase Flow Loop Facility
Research Studies with Multiphase Flow Loops
- Multiphase Flow Patterns
- Study of Flow Patterns under Pipe Inclination
Gas-liquid flows in pipes have been studied in the past. Flow patterns change with the ratio of gas to liquid flow rate. Detailed flow regime maps exist for horizontal and vertical pipes. But there is little information on the flow regime when the pipe is neither horizontal nor vertical.
Flow
patterns may change for inclinations less than 0.5 degree. Upward inclinations
enhance slug flow while downward inclinations enhance stratified flow. Also, the
diameters of the pipes have a strong effect on the flow patterns. For a given
flow rate and composition, the flow regime of a particular configuration can be
determined in the flow loop.
- Study of Oil/Water Transport
Corrosion in oil production is caused by the presence of water. At low water cuts and under turbulent conditions, water is dispersed in the oil phase and water is entrained by the high flow rates, these conditions maintaining a low corrosion rate. But with higher water cuts and lower turbulence, water separates and a water phase is formed in the flow, changing dramatically the corrosion conditions.
| In a flow loop, the oil/water flow characteristics can be investigated. With Plexiglas pipes, the effects of variations of water cut, flow rate, and pipe inclination on the flow patterns can be visualized and incorporated into mathematical models. |  |
- Evaluation of Corrosion Inhibitors
As oil and gas production tends to operate under extreme conditions, the needs for corrosion inhibitor testing under turbulent flow are increasing.
Corrosion inhibitors have been largely tested in autoclaves for estimation of their corrosion protection effectiveness. But the correlation between inhibitor performance in laboratory and field tests is still a challenge. Some corrosion inhibitors, which have performed well in laboratory tests, have not shown good efficiency in the field. Thus, the demand for corrosion inhibitor testing under more realistic flow conditions is still important.
Flow
loop systems recreate the flow conditions of the field and give valuable insights
on the corrosion protection effectiveness of inhibitors. The selected inhibitor
will be the one that shows good performance under actual flow conditions. Inhibitor
selection is then based on the most valid criterion.
- Mechanistic Studies of Corrosion Inhibitors
Large diameter flow loop systems simulate the real flow conditions encountered in oil and gas pipelines. Electrochemical probes are installed in the test section with coupons for corrosion monitoring. The inhibition performance of various chemical formulations can be investigated under turbulent flow conditions, and the electrochemical techniques bring information on the corrosion protection mechanisms of these inhibitors. Correlation between inhibitor formulation, inhibitor concentration, length of exposure, passive film formation and structure can be studied.
- Evaluation of Drag Reducing Agents (DRA)
Corrosion control methods in pipelines have been generally divided between two choices: the use of chemical inhibitors for corrosion protection of the pipe internal surface or the use of corrosion resistant alloys under corrosive conditions. A new approach has come forward for a cost-effective transport of oil and gas: drag reduction. With the use of Drag-Reducing Agents (chemicals, which increase fluid flow and reduce pressure loss), friction decreases in the turbulent flow.
Slug flow represents the most erosive-corrosive conditions encountered in multiphase pipelines. By using Drag Reducing Agent (DRA), the flow regime can be modified and the slug frequency can be reduced, resulting in less corrosive conditions. In a flow loop system, the effect of DRA on the flow regime and corrosion rates can be investigated.