Electrochemical and Corrosion Measurements in Laboratory Autoclaves

Materials Research and Corrosion Testing
When corrosion research laboratory equipment is needed, Cortest Autoclaves have demonstrated their great capabilities worldwide. They are a certification of quality and reliability.

The process environments are simulated in the autoclaves for material characterization and process optimization. Corrosion testing, materials and electrocatalysis research are conducted in the most corrosive environments under safe and efficient operation. Cortest Autoclaves have been largely used in aggressive environments like H₂S environments and in supercritical waters.

Weight Loss Corrosion Coupons
Corrosion coupons provide information on metal loss and corrosion rate but also on the distribution and forms of corrosion. Technical standards for corrosion testing include ASTM G1 for metal loss calculation, ASTM G46 for analysis of localized corrosion, and NACE TM-01 for corrosion testing.

Corrosion coupons still represent the most reliable method. The corrosion rates as well as the forms of corrosion can be determined. But while corrosion coupons are the basis of comparison, they only give results on the averaged corrosion rates over the period of the experiment. No on-line measurement is possible. For continuous corrosion measurements, corrosion probes must be used.

Corrosion coupons fixed in a static autoclave evaluate the corrosion rates of materials as well as the solution corrosivity. Corrosion tests are conducted in autoclave systems to detect and measure uniform and localized corrosion, and environmentally induced cracking corrosion. The susceptibility of materials to Environmentally Induced Cracking (EIC) like Stress Corrosion Cracking (SCC) and Hydrogen Induced Cracking (HIC) can be performed with U-bend or C-ring specimens.

Stirred Autoclave Systems
While coupons installed in a static autoclave provide useful corrosion test measurements, the capability to maintain a uniform chemistry throughout the autoclave vessel is generally beneficial.

A) Stirring Systems
A magnetic stirring system for heavy duty applications is available. It includes a magnetic drive, impeller, DC motor/pulley assembly, and motor speed control. Tachometer and LED provide an accurate measurement and display of speed rotation in Rotation Per Minute (RPM). The stirring system is available with safe certification for hazardous locations (H₂S environments). The shaft and accessories are provided in Hastelloy C-276.

2 options are available: A propeller is installed on the shaft. Coupons are fixed, and the shaft and propeller stir the solution; Coupon holders are directly installed on the shaft and the rotating shaft spins the coupons during the experiments.

B) Recirculating Loop for Stirred Autoclave
In a closed system, corrosion products form on the metal specimens and may dissolve into solution. The dissolution of species into solution may modify the experimental conditions. With a Recirculating Test Loop (RTL), the solution is refreshed and the autoclave composition is perfectly controlled.

Cortest also features a cylinder electrode installed on the rotating shaft. The cylinder electrode used in the Cortest autoclave offers the possibility of conducting experiments under high-pressure and high-temperature conditions with a rotating electrode. The electrode is electrically isolated from the shaft. An electrical connection to the cylinder electrode allows the end-user to conduct electrochemical measurements.

Pressurizing Autoclaves with Corrosive Gases
In the oil and gas industry, corrosion testing under high temperature and high pressure generally involves the presence of CO₂ and H₂S gases. These gases produce the acidity that generates the high corrosivity of the solution.

Pressurizing the autoclave to the desired values of partial pressures of CO₂ and H₂S is not an easy task, since CO₂ and H₂S dissolve in brine and water solutions. Their concentrations have a strong influence on the experiment results. When the autoclave is pressurized, the partition of CO₂ and H₂S between the water and gas phases must be taken into account. Moreover, the solubilities of gases in water are a function of temperature.

Several methods can be used in practice but all are not equivalent. The final method also depends on the type of experiments that is performed. Cortest engineers can advise buyers of Cortest autoclaves on how to pressurize the vessels for an accurate and efficient operating procedure.