ICMT Instrumentation and Equipment

Two large scale multiphase flow corrosion systems are mounted on an inclinable rig with the capability of operating at 0-90o inclination. This enables simulations of various multiphase flow regimes typical for wells and pipelines. The High-Pressure system and the Low-Pressure system, both 4” I.D. have capabilities ranging from corrosion experimentation at elevated temperatures and pressures to multiphase flow characterization and visualization to (see Figure 1).

The inclinable multiphase high-pressure system has all 316 stainless steel wetted parts, giving it the ability to operate at temperatures up to 120°C and pressures up to 70 bar in single-phase, two-phase (oil-water or gas-water) and three-phase (oil-gas-water) flow at any angle of inclination. Multiphase flow patterns such as: stratified, slug, annular-mist, etc., can be achieved. Water chemistry monitoring and control enables long term operation under stable and realistic conditions, simulating realistically situations found in the field, including use of crude oils and injection of corrosion inhibitors. The inclinable multiphase low-pressure system is made from acrylic and is intended for corrosion and water wetting experimentation in two-phase oil-water flow. In both systems, oil and water are pumped independently using progressive cavity pumps and a blower is used to move the gas. A liquid gas separator and an oil-water separator are integrated into the system, enabling complete separation and independent metering of the oil, water and gas flow (see Figure 2).

Both systems have multiple test sections for insertion of corrosion probes (LPR, ER, coupons), sampling ports, pressure taps for pressure drop and flow regime determination, water wetting conductivity probes, etc. (see Figure 3). The transparent acrylic test section allows for visualization of multiphase flow characteristics with high-speed video imaging (see Figure 4). and high-speed tomography (see Figure 5). The operational conditions for the inclinable High-Pressure system are shown in Table 1.

The H2S multiphase flow corrosion system is a large scale horizontal flow loop (see Figure 6) able to accommodate partial pressures of H2S up to 150 mbar, various liquid hydrocarbons and water. It is ideally suited for studies of sour corrosion in multiphase flow seen in the field, including the effects on corrosion inhibition. The 2000 L system is comprised of 4" ID piping, made from Sch 80, Hastelloy© C-276 for resistance to corrosion and stress corrosion cracking. Two progressive cavity pumps are used to move liquid and gas, and three separate test sections for corrosion monitoring operate simultaneously, one in single-phase water flow, the other two in multiphase gas-liquid flow. A variety of multiphase flow regimes including stratified, slug, annular-mist, etc., can be achieved. With system temperature control up to 90°C and total pressure from atmospheric to 30 bar, accurate water chemistry and multiphase flow control and monitoring, simulation of complex field conditions can be accomplished on a large scale in a safe operating environment.

The H2S multiphase flow corrosion system is located in a large isolated environmental chamber for better control of temperature and containment of hazardous gases. Negative pressure in the chamber, a multitude of H2S monitoring sensors, scrubbing and combustion of exhaust gases contributes to safe operation of the H2S multiphase system, even on long experiments, lasting weeks or even months. All operational controls for the hydrogen sulfide test loop are located just outside the environmental chamber providing a higher level of safety for the operator and more convenience for data collection. Safety is of paramount concern; hence the technical staff, graduate students and research scientist who operate the system are fully trained in safety monitoring and procedures.

Various types of corrosion-monitoring equipment can be installed in each of two three test sections, such as: corrosion probes (LPR, ER, coupons), or coupons for weight loss measurement. The operational conditions for the inclinable loop are shown in Table 2.

Investigation of so called Top of the Line Corrosion (TLC) also known as dewing corrosion or corrosion under condensing conditions, can be performed in two large wet gas flow loops (see Figure 7, Figure 8, and Figure 9 ).These loops are comprised of a large tank (1000L) holding the bulk liquid phase, a gas blower and a liquid pump (just the TLC loop #2), and a loop of 4”ID stainless steel pipes (30 m total length). Only gas saturated with water vapor is circulated. The pipe walls and the test sections are cooled to create condensing/dewing conditions. Different test sections enable introduction of various monitoring devices to measure corrosion rate, condensation rate, pressure drop, temperature, gas velocity, droplet visualization, etc. Sampling ports enable identification of gas and liquid composition. The main operational conditions are shown in Table 3.

An example of one of the many possible configurations of the transparent low-pressure low-temperature corrosion multiphase flow systems is the so called “hilly terrain system” (see Figure 10 ). which allows the simulation of corrosion in multiphase water/gas flow in the vicinity of road and river crossings and in hilly terrain topography with short, abrupt inclination changes. The flow loop consists of a 4”ID, 18- m long transparent acrylic line carrying water and gas. The multiphase flow moves over a horizontal distance of 6 m before reaching the crossing section, consisting of four nine-diameter radius bends with 2 m stretches for the riser, crossing, and downcomer sections. The fluids then move through a 4 m horizontal discharge section into a separation tank. This configuration creates a highly complex multiphase flow patterns particularly in the vicinity of the bends. At any given gas and liquid flow rate, this system can experience nine different flow patterns, in different sections, at the same time, some of them very “violent”. This flow loop is particularly suitable for studies of disturbed multiphase flow on corrosion, including the effect on corrosion inhibition. The operational conditions for the hilly terrain loop are shown in Figure 10.

The thin channel flow cell (TCFC), which is depicted in Figure 11 is a small scale single-phase flow loop that enables well controlled hydrodynamic conditions in the test section. The test section is in the form of a thin channel with a large aspect ratio (3 mm high and 100 mm wide) and almost 700 mm in length. This produces a uniform 2-D flow field that is fully understood and readily modeled. The TCFC can be used to conduct corrosion tests at low and high flow rates (up to 17 m/s). The high velocity between two plates generates a very high wall shear stresses (up to 550 Pa). This equipment is ideal to study the effects of high wall shear stress on the removal of protective corrosion product layers, efficiency of corrosion inhibitors, etc. Electrochemical probes and weight loss specimen are flush mounted at the bottom of the test section and they can be removed at different times throughout an experiment. In long term experiments, the chemistry of the solution (e.g. pH, Fe2+) is controlled by using inline ion-exchange resin units. The operating specifications for the low TCFC are provided in Table 5 .

The high pressure thin channel flow cell (HP-TCFC) is a similar device to the LP-TCTFC, with the specific capability that it can operate at very high CO2 partial pressures, up to 140 bar. This includes conditions where CO2 is liquid or even supercritical, and very high flow rates and wall shear stresses can be reached in the test section. With small modifications this makes is suitable for studies of downhole conditions and those seen in enhanced oil recovery (EOR) and carbon capture and storage (CCS) facilities, including corrosion inhibitor testing at extreme conditions (see Figure 13 ). The operating conditions in the HP-TCFC are listed in Table 6. Operational conditions for the HP-TCFC are given in Table 6.

The Hastelloy small scale flow loop is a 5-liter fully contained system with all wetted parts made from Hastelloy C-276, which can be used in H2S environments (see Figure 14 and Figure 15 ). It is rated to safely operate at pressures up to 120 bar. There are two test sections with an impinging jet and pipe flow configurations, which are capable of electrochemical measurements or weight loss measurements in single-phase flow. A special inhibitor injection port, located in one of the flow channels, provides the ability to add inhibitor to an operating system. The loop can beo equipped with a water chemistry control system for long term corrosion experiments. The operating specifications for the small scale flow loop are provided in Table 7.

The 316 stainless steel autoclaves at the ICMT come in a variety of sizes (1, 2, 4, 7, and 20 L in volume), see Figure 16 and Figure 17. They are equipped with online electrochemical measurement systems, including rotating cylinder electrode (RCE) and in some cases flow tube configurations. Largest of them, the 20 L SS316 autoclave (see Figure 17) includes a HPHT sapphire window to enable visual observation of the fluid phases and the specimen held inside. Due to its large volume, it allows for sampling for species concentration measurement, without significantly affecting the composition of the fluids held within. Furthermore, water chemistry is much more stable so that changes due to accumulation of corrosion products are much slower due to the large volume to surface ratio. Therefore this type of autoclave is very suitable for long term corrosion experiments under HPHT conditions. While the smaller autoclaves can handle pressures up to 350 bar and 300°C, the large 20 L autoclave is limited to 150 bars as the maximum operating pressure.

High pressure Hastelloy autoclaves are specially designed to handle H2S/CO2 systems. A schematic and image of a 7 L Hastelloy autoclave are shown in Figure 18. The autoclave is equipped with electrochemical measurement capabilities. The operating conditions for the autoclave are provided in Table 9.

A 20 L Hastelloy autoclave shown in Figure 19 is custom designed to study so called top of the line corrosion (TLC) at high pressure in CO2/H2S environments. Mild steel specimen (5.7 cm diameter) are mounted on the top lid which is equipped with a cooling system to achieve condensing/dewing conditions in the gas phase. Mild steel specimen can also be suspended in the gas phase in order to simulate very low condensation rates. In addition, the efficiency of corrosion inhibitors can be evaluated in the bulk liquid phase (in the solution at the bottom). The operating specifications for this autoclave are provided in Table 10.

The so called "doughnut cell" apparatus (named due to its doughnut like shape of the flow space) makes it possible to conduct studies of water wetting and corrosion in two-phase, oil-water flow on a much smaller scale compared to that done in flow loop testing (e.g. inclinable loop). The doughnut cell tests take only about 10 L of oil, compared to 2000+ L used in the flow loop test. Water wetting and corrosion in a two-phase oil-water flow can therefore be simulated much quicker and in a much less expensive way. Figure 20 shows the 316 stainless steel doughnut cell. The doughnut cell works by introducing water and oil (separately or as an emulsion) into a circular annulus, which is formed between two concentric cylinders (outer and inner, shown in green in Figure 20 on the right). The top ring of the flow channel is rotated driven by a carousel (brown component in Figure 20 on the right), to induce shear flow in the circular annulus. The bottom ring of the flow channel is static (shown in gray in Figure 20 on the right) equipped with flush mounted arrays of conductivity pins for the wettability studies and corrosion probes (LPR, EIS, coupons, etc.). The cell is also equipped with heating and cooling to achieve temperatures different from the ambient.

Glass cells are suitable for experiments on a small scale done much more quickly and inexpensively than in large multiphase flow loops or autoclaves. The ICMT has many different customized glass cell setups to study CO2/H2S corrosion and inhibition under strict flow and water chemistry control. Below is a description of some the of the glass cell configurations used at the ICMT.

Figure 21 shows a glass cell setup specially designed to hold multiple electrochemical and weight loss specimen. Flow is controlled by an impeller which eliminates the centrifugal forces encountered in a rotating cylinder electrode. All the specimen are located at the same height and distance from the impeller having the same hydrodynamic and mass transfer conditions. In order to perform long term corrosion experiments, the water chemistry is controlled (pH and Fe2+ concentration) with ion-exchange resins. Specimen can be removed easily at different times without oxygen contamination.

Another way water chemistry is controlled in long glass cell experiments involves a flow-through system where the solution is continuously replenished (Figure 22). Persistency of corrosion inhibitors can be studied be studied using a similar setup.

Glass cells in the standard three-electrode RCE arrangement (Figure 23) are typically used for short term experiments to study corrosion and corrosion inhibition mechanisms. They are readily multiplexed to speed up the collection of results.

Glass cells with EQCM (Electrochemical quartz crystal microbalance) and QCM (Quartz crystal microbalance) are currently used at the ICMT to study the kinetics of FeS and FeCO3 formation and adsorption of corrosion inhibitors. Experiments can be performed in the liquid phase or the gas phase (see Figure 24).

The effect CO2, H2S, organic acids, and water condensation rate, on top of the line corrosion (TLC) is performed in glass cells custom designed to simulate a TLC scenario. Mild steel specimen are flushed mounted at the top of the lid and their temperature controlled to achieve different water condensation rates from the gas phase. Peltier coolers are used to precisely control the temperature of the specimen surface and a boroscope is used to observe the formation of droplets. Performance of volatile corrosion inhibitors can be studied in this type of glass cell setup.

A separate chamber holds a number of pieces of equipment related to studying corrosion of steel at high temperature in hydrocarbons as related to conditions seen in refineries. They include a battery of 316 SS 1 L stirred autoclaves (see Figure 26), a low pressure single-phase creeping flow system called a Flow Through Mini Autoclave (see Figure 27), a custom designed flow through autoclave with a rotating cylinder specimen called the High Velocity Rig (Figure 28), and a two-phase oil-gas flow through system named the Annular Flow Rig (see Figure 29).

Surface analysis of the steel specimen exposed to corrosive environments is extremely important to understand corrosion mechanisms. The ICMT has a SEM JEOL JSM-6390 (Figure 30) that is available to ICMT students and staff. The SEM is capable of up to x300,000 magnification which permits analysis of morphology and chemical composition of metal surfaces and corrosion products. In low-vacuum mode the instrument allows the analysis of biofilms or specimen that contain water or hydrates. Figure 31 shows two images taken with our SEM showing crystals of FeCO3 formed on steel specimen exposed to top of the line corrosion.

It is possible to perform chemical analysis (qualitative and quantitative) of the corrosion products thanks to an energy dispersive X-Ray spectrometer (QUANTAX 400 with XFlash 6) attached to the SEM. The silicon drift detector allows the acquisition of fast elemental mappings (Figure 32), line scans and point analyses.

Specimen surfaces are routinely characterized using a high resolution, optical 3D micro coordinate surface measurement system from Alicona (InfiniteFocus), Figure 33. The InfiniteFocus system allows capturing of sharp and brilliant images with a virtually infinite-depth-of-focus. In contrast to conventional light microscopy, 3D images of surface features at 1000x magnification can be captured, visualized and analyzed. This enables measurement of pit depth and subsequent quantification of localized corrosion rates. The images below, Figure 33(b) show 3D and profilometry data for a X65 carbon steel sample exposed to CO2 corrosion.

EnviroCam - a video system that enables in situ observation at pressures up to 8 bar and temperature up to 90°C in its current configuration (see Figure 34). This frontlit high resolution system is designed by Enviroptics and is equipped with a camera, optics, and lighting, and can be directly inserted into our multiphase flow loop via a custom designed port. The system was most effectively used in study of Top of the Line Corrosion (TLC) where live visual feed of the steel sample surface focused on the process of water condensation as it affected localized corrosion attack (see Figure 35).

The AFM is one of the most recent acquisitions the ICMT. AFM is a high-resolution imaging technique that can resolve features as small as an atomic lattice, for either conductive or non-conductive specimen. AFM provides high-resolution and three-dimensional information, with little sample preparation. The technique makes it possible to image in-situ, in fluid, under controlled temperature and in other controlled environments. Electrochemical measurements can also be performed in parallel using a specially designed specimen holder.

Being a piezoelectric device, quartz crystal microbalance QCM relates the mass change per unit area at the electrode surface to the resonance frequency change of a quartz crystal. The QCM200 Quartz Crystal Microbalance from Stanford Research Systems can be used in-situ in vacuum, gas, or liquid environments. With the high precision frequency measurement, QCM can detect a mass change on the scale of nanogram, which makes it a superb mass change detector for a large variety of applications, such as: corrosion, precipitation/dissolution, adsorption/desorption, etc. Besides the ability of monitoring the in-situ mass change in high resolution, QCM also allows electrochemical measurement to be conducted simultaneously (EQCM). At ICMT the EQCM has been extensively used in corrosion inhibition studies as well as related to precipitation/dissolution of iron carbonates and sulfides.

The ICMT possesses eight Gamry Instruments Reference 600 potentiostat/galvanostat/ZRA instruments and one Series G 300 potentiostat/galvanostat (see Figure 39) as well as two Princeton Applied Reseach VersaStat 3 potentiostat/galvanotat instruments (see Figure 40).

The Gamry Instruments Reference 600 is a high-performance, research-grade potentiostat/galvanostat/ ZRA designed for fast, low-current measurements. It does well for a variety of applications such as physical electrochemistry (especially at microelectrodes), fast cyclic voltammetry, electrochemical corrosion, electrochemical noise measurements, testing of paints and coatings, as well as sensors. It has a number of auxiliary input and outputs designed to help interface or control ancillary equipment such as a rotating electrode. It also has a thermocouple input for temperature measurements. The following electrochemical measurements can be performed:

• DC Corrosion - Standard DC corrosion tests such as polarization resistance, potentiodynamic, cyclic polarization, and galvanic corrosion in addition to a number of others.
• Electrochemical Frequency Modulation - A non-destructive corrosion rate measurement technique. It allows for measurement of the corrosion rate without prior knowledge of the Tafel constants. In addition, the technique determines the Tafel constants and provides 2 internal validity checks.
• Electrochemical Impedance Spectroscopy - includes experimental scripts for potentiostatic, galvanostatic and hybrid impedance spectroscopy experiments in addition to single frequency techniques like Mott-Schottky. A unique power-leveling multisine technique can be used that improves signal-to-noise across the spectrum. On the analysis side, it provides tools for fitting spectra to equivalent circuit models, Kramers-Kronig transform for data validation and a graphical model editoA more general form of electrochemical noise testing. It is also an ECM8 Multiplexer compatible electrochemical noise software package.
• Physical Electrochemistry - Techniques such as pulse voltammetry, square wave voltammetry, and associated stripping techniques such as anodic stripping voltammetry.
• Pulse Voltammetry - Techniques such as cyclic voltammetry, chronoamperometry, and chronopotentiometry and derivatives of these techniques.
• Electrochemical Signal Analyzer - Designed specifically for the acquisition and analysis of time-dependent electrochemical noise signals. Cell voltage and current are continuously monitored at rates from 0.1 Hz to 1 kHz. A full featured set of analysis tools provides powerful analysis features such as statistical analysis, detrending, impedance spectra, and histogram analysis.
• Critical Pitting Temperature - controls a Gamry Potentiostat, TDC4 Temperature Controller, and associated accessories to automatically measure the Critical Pitting Temperature of a material.

A probe flush mounted on the pipe wall that can directly measure wall shear stress - WSS (see Figure 41) consists of a floating element with a supporting cantilever, two optical strain gauges, and a probe enclosure. The circular-shaped floating element is set in a cylindrical enclosure with a fine external thread to ensure a flush alignment with the pipe wall. Two optical strain gauges, with fiber Bragg gratings (FBG), are attached to the cantilever. The FBGs provide the direct measurements of lateral displacement for calculation of WSS. The performance of the probe has been verified in single phase flow using the Thin Channel Flow Cell (TCFC) and it was further used for analysis of flow characteristics and wall shear stress in two-phase and three-phase flow.

The semi- automatic Krüss - K20 force tensiometer is available in order to precisely measure surface, and interfacial tension between various liquids and gases as well as contact angle between liquids and solids, using Du Noüy ring, Wilhelmy plate and ring tear-off methods. These are important parameters affecting multiphase flow, water wetting and inhibitor performance. The thermostat jacket provides reliable measurement for temperatures between -10 to 100 °C.

Custom designed goniometer is suitable for measurements of surface wettability in gas/liquid and liquid/liquid environments. The setup shown in Figure 43 enables measurements of contact angles of sessile liquid drops on a given test specimen surface. The goniometer consists of two main parts, the test cell or vessel and the image capture system. The vessel is made of 316 stainless steel and has 4” I.D. and 6” height. There are two 2” aligned circular openings on its sides to accommodate flat glass windows that allow the imaging of the internal fluids without distorting of the droplet image. The vessel has ports at its bottom and top to allow droplet injection, drainage, insertion of pH probe and gas bubbler. The internal fluids can be heated up to 80°C, and pressurized up to 5 bar.

Contact angles of liquid droplets in positive buoyancy (e.g., oil drop in water) or negative buoyancy (e.g., water drop in oil) can be measured due to special design of the specimen geometry and its holder (shown in Figure 44). Experiments on tilted surfaces are possible, by adding accessories to the specimen holder.

The image capture system is composed of a camera, a backlight, a PCI card and image analysis software. The camera used is IMAGING PLANET® model 221-XS monochrome CCD camera with 768 x 494 pixel array and 570 horizontal lines of resolution. The PCI card installed in the computer connects to the camera to capture the image of a droplet displayed on the computer screen using Snagit® software. Contact angles are measured using image analysis software such as RINCON® image or similar. Figure 45 shows examples of water-in-oil contact angles measured in clear model oil environment on hydrophilic and hydrophobic carbon steel surfaces.

The Buhler EcoMet 3000 is a variable speed grinder-polisher. It has an aluminum variable speed platen (10 to 500 rpm) and an universal specimen mount. A pop-up water-dispensing arm can be positioned over the platen and the amount of water dispensed can be regulated by the flow control valve. It is used for polishing of metal samples to a very fine finish.

Coating a specimen with a precious metal such as gold, palladium or an alloy increases surface conductivity, which produces the best images in SEM. The HUMMER 6.2 performs sputter coating, a cold process in which ions impacting a metal source dislodge metal atoms. The atoms disperse throughout the process chamber to uniformly coat irregularly shaped specimens without thermal damage. Sputter coating produces high quality coatings whose thickness is repeatable and readily controlled.

The Karl Fischer titration method is suitable for precise measurements of water content dissolved or dispersed in oil or other immiscible liquids. The residual water content in oils can be relevant for water wetting and corrosion studies, as well as other specific studies related to water dropout and multiphase flow behavior in pipes.

The ICMT has two Karl Fischer units one for Coulometric titration and one for Volumetric titration. A summary of their specifications is as follows:

Coulometric titration unit (suitable for very low water concentrations):

• Brand and model: KEM, MKC-610-DT
• Measurable water content range: 10 μg to 100 mg
• Titration cell: two-component electrolytic cell (Diaphragm cell)
• Sensitivity: 0.1 μg H2O

Volumetric titration unit:

• Brand and model: KEM, MKA-610-ST
• Titration volume range: 0.005 to 100 ml
• Burette capacity and precision: 10 ml ± 0.015 ml
• Range of processed water mass: 0.1-500 mg (max value depends on type of reagent)
• Measurable water content range: 10 ppm to 100%

The Aquamax TAN Titrator conforms to ASTM D664 (potentiometric titration) and it is used for evaluation of acidic components in petroleum products, lubricants, and transformer insulating oils. Our TAN Titrator is used mainly for measuring the Total Acid Number (TAN) of crude fractions and/or model oils that mimic chemical compositions of real crudes. The measurement results are expressed in mg KOH/g oil.

The 490-GC PRO Micro-GC (Agilent) and the Inficon Micro GC 3000 are gas chromatographs that use a narrow bore capillary column together with a miniaturized detector. The instrument is delivering a rapid separation of permanent gases and vapors providing a fast and accurate analysis of gas samples. It is used for example to measure the H2S concentrations in gas samples collected from autoclave or flow loop headspace (during/at the end of tests). The Micro-GC can be also be reset and calibrated for measurements of CO2 concentrations in gaseous samples.