Hastelloy Autoclaves
Corrosion inhibitors for severe environments require test conditions that simulates the system pressures and temperatures in order to realistically challenge the effectiveness of the products.
Cormetrics uses 300 mL UNS N10276 (Hastelloy C) autoclaves, jacketed with electric heaters regulated by temperature controllers. The units can be pressurized to over 5500 kPa at temperatures up to 170°C. The units are stirred magnetically to impart sufficient agitation to perform valid electrochemical measurements.
The autoclaves hold a triangular array of electrodes; with a UNS N10276 reference and mild carbon steel working and counter electrodes. The electrochemical measurements are made using a Gamry potentiostat connected to several cells via a multiplexer.
The cells are purged and pressurized with a gas mixture blended according to the field acid gas content (H2S, CO2, methane or nitrogen). The cells are placed in the jacket heaters and brought to system temperature using the temperature controller. Corrosion rate (LPR) readings are made every 30 minutes for the period of the test, usually 96 hours. The working and counter electrodes are cleaned, weighed for weight loss corrosion rate and photographed for the final report.
The test protocol can be modified to consider partitioning of inhibitors, use of mushroom cap coupons for under deposit corrosion or the crevice electrode.
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Rotating Cylinder Apparatus
The RCE allows testing of the corrosion inhibitor in a controlled shear environment. The rotating cylinder apparatus is designed to create a known and constant shear stress on the inhibitor film by spinning the working electrode at speeds up to 5,000 rpm. This way, surface shear stress up to 32 Pa may be readily obtained. The corrosion cell itself consists of a glass flask jacketed with a circulating glycol/water mixture keeping the cell at a constant temperature. A positive pressure, anaerobic environment is maintained during a test by means of a constant CO2 purge. Electrochemical measurements are performed at intervals during the test, then the results are validated by weight loss and visual examination of the test element. This powerful technique allows rapid comparison of the performance of corrosion inhibitors in various applications. The tests for which RCE is particularly well suited are:
- Batch corrosion inhibitor film persistency and stability over time.
- Performance of continuous chemicals under controlled shear.
- Effect of water miscible chemicals such as methanol on inhibitor performance.
Wheel Test Apparatus
Our corrosion testing laboratory also includes the Wheel Test apparatus for corrosion inhibitor performance testing. The Wheel Test is typically used as an initial test of all corrosion inhibitors in the brine. The brine is de-aerated with CO2 for 2 hours and the purged brine is transferred to the wheel test bottle where inhibitor is injected at prescribed treatment levels. A CO2 headspace is provided and the test proceeds onto the wheel test apparatus. Each inhibitor dose is tested in triplicate. An additional three bottles will be run with no inhibitor to determine a blank corrosion rate. The coupons used in the wheel test are made of UNS G10100 mild carbon steel shim stock (15 cm x 1.3 cm x 0.2 mm). The sealed bottles are placed inside a wheel test apparatus set to a maximum temperature of 75°C and rotated for 72 hours. Weight loss on the coupons is recorded over the exposure period to determine the corrosion rate and coupons are inspected to document if localized or general corrosion has occurred.
Potentiostat
Cormetrics has 3 high-sensitivity potentiostats for performing electrochemical measurements in our autoclave and RCE experiments. The potentiostat has a potential range of ±12V and maximum current of ±1 A. It is able to take current readings over 9 ranges with a minimum resolution of 3.3 fA. In combination with the attached multiplexer we can perform these measurements over multiple cells.
Depending on the test requirements, the following DC electrochemical methods can be used to monitor corrosion during the exposure period:
Test design is to record current flow and material potentials between dissimilar metals and report on corrosion rate identifying the extent to which one material is anodic to the other. Weight loss corrosion rate are also recorded. The standard experiment is completed over a four day period in the pressurized autoclaves or over a two day period at atmospheric pressure in the rotating cylinder electrode apparatus.
Test design is to investigate the pitting and repassivation of materials. Also used to indicate inhibitor influence on pitting potentials. Standard test is run in the autoclaves over a two day period. Reporting includes discussion on the open circuit, pitting and repassivation potentials.
Test design is to record current flow and material potentials between dissimilar metals and report on corrosion rate identifying the extent to which one material is anodic to the other. Weight loss corrosion rate are also recorded. The standard experiment is completed over a four day period in the pressurized autoclaves or over a two day period at atmospheric pressure in the rotating cylinder electrode apparatus.
Test design is to apply a small potential to the electrode and determine the current response. This technique is used to evaluate materials and can be informative for corrosion inhibitor testing. The technique is combined with the CPP scan to determine the applied potential for the test and is typically run over a three day period.
High Sensitivity Mass Balance
Cormetrics uses a high precision analytical balance that is calibrated regularly to ensure accuracy and precision of all mass measurements. The balance has a readability of 0.01 mg allowing for precise determination of mass loss when determining weight loss corrosion rates. The balance is also used in measuring salts in the preparation of accurate synthetic brines.
Stereo Microscope
Cormetrics uses a low power (7-45X) magnification microscope in the examination of electrodes and failure cut outs. The stereo microscope permits a 3 dimensional view of the sample and better visualisation when examining corrosion defects. The trinocular design allows for the attachment of a digital camera for detailed micrographs.
Wettability Test Cell
The wettability test cell is a test cell used in G205 testing to classify crudes. The cell is operated under pressure and contains a central reference pin surrounded by 20 measuring pins arranged in a circular pattern. Wettability is the determination of a crudes ability to maintain an oil wet surface. The measured resistance between the steel pins and reference pin is the test criterion. The crude oil is then classified as water-wet, mixed-wet or oil-wet.
EIP Circulating Apparatus
The EIP (Emulsion Inversion Point) apparatus is used in G205 testing. The contained loop apparatus circulates a crude brine mixture under atmospheric conditions at controlled circulation rates. Brine is added in incrementally and the point at which the emulsion changes from a oil external to water external phase is determined by resistance measurement across to two control pins.
The apparatus is used to create a partitioned brine with suspended oil to evaluate the corrosion rate in an RCE experiment. This allows for determination of the potential corrosivity versus inhibitory effect of a crude.
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