Materials Performance Supplements

CORTEC 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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VAPOR PHASE CORROSION INHIBITORS passive range for these alloys when inhibi- tors were added. These inhibitors acted as effective cathodic inhibitors. The inhibitor changed the reactivity by reducing the pH level, increased the passivation range sig- nificantly, and was beneficial in reducing localized corrosion damages. As demon- strated in these polarization curves, exten- sion of the passive zone contributes to the stability of the protective oxide film over a wider electrochemical range, resulting in a more stable passive film, and shifts the crit- ical pitting potential to higher levels. Corrosion rate measurements based on the linear polarization rate are shown in Figures 4 to 6. The effectiveness of these VCI products is confirmed in various water chemistries including fresh and salt water. The corrosion rate dropped from ~10 mpy for the salt solution to less than 1 to 2 mpy when various inhibitors were added. The effectiveness of these inhibitors was remark- able in the fresh water (less than 0.4 mpy). The corrosion behavior of low CS was investigated using EIS in different salt con- centrations. Various Bode plots are shown in Figures 7 to 9. These results showed a significant increase in polarization resis- tance when inhibitors were added. Mea- sured polarization resistance jumped from 2,000 to 3,000 Ω-cm 2 to more than 30,000 to 110,000 Ω-cm 2 . These increases in polariza- tion resistance are equivalent to a signifi- cant decrease in the corrosion rate. Figure 10 summarizes the average mea- sured corrosion rate by different electro- chemical techniques. These results reaf- firmed the necessity to add these inhibitors to testing media during hydrotesting. The laboratory test method evaluations of the VIA of these VCI products are shown in Figures 11 to 12. Samples were visually inspected and their surface conditions were documented after VIA tests were com- pleted using optical digital microscopy and SEM. Based on three sets of VIA tests, the observation showed that the control had a Grade 0 (severe pitting corrosion), while the addition of VCI-A, VCI-B, and VCI-C resulted in a significant improvement to Grade 3 (almost no corrosion attacks). These results showed that these inhibitors have a very strong VIA. Additionally, any leftover residue of hydrotesting solution in pipes will be beneficial and provide extra protection during a storage period, con- FIGURE 10 Corrosion rate measurements of UNS G10180 steel using different electrochemical techniques (cathodic protection, EIS, and Rp/Ec trends) at different aqueous solutions. FIGURE 9 EIS Bode plot of UNS G10180 steel in 1.0% VCI-C at different aqueous solutions. air, water vapor, and VCI, and (2) corrosion protection are evaluated in this test method. The VIA tests consist of four steps of sample conditioning or saturation for 20 h at 22 °C, a cooling cycle at 2 °C, and prewarming at 50 °C, followed by 3 h at 22 °C for specimen con- ditioning. After the last conditioning period, the steel samples were inspected for visible water condensation. Following verification of water condensation on each sample, visual examination of the surface was done and microscopic observation was conducted to determine the corrosion rating for each sample. The corrosion criteria for rating steel specimens consist of Grade 0 through Grade 4. To have a valid test, the control sample must have Grade 0; samples with no inhibitor received the worst grade. The control samples consistently rated a Grade 0 for all VIA tests, therefore validating the test method. Relative humidity and the tem- perature of each test jar were monitored by inserted sensors and data logging software. Post-test evaluation of the surface condition of exposed samples involved digital light microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy, and x-ray photoelectron spectroscopy. Results and Discussion Figures 1 to 3 show the polarization behavior for UNS G10180 steel in 1.0% inhibitor (different VCI products) in dif- ferent salt solutions. Th e most notice- able changes are the positive shift in the breakdown potential and expansion of the 10 JUNE 2019 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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