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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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Application of Vapor Phase Corrosion Inhibitors for Contaminated Environments trary to the stagnant wet condition that testing without an inhibitor might cause. The VIA visual observations are shown in Figure 11. Figure 12 shows SEM micro- graphs of the steel sample after VIA tests. The high-resolution SEM images show a sig- nificant improvement for VCI-A, VCI-B, and VCI-C with no sign of any pitting corrosion. Figure 13 shows the effects of different corrosion inhibitors on the mechanical behavior of low CS. Tensile tests on the exposed samples after four-week immer- sion tests indicated that the level of cor- rosion attacks were minimized , and no sign of any deterioration in ductility of the exposed samples was detected. Inhibitor Adsorption Mechanism The adsorption isotherm relationship between surface coverage and tempera- ture for the VCI-A, VCI-B, and VCI-C inhib- itors on the surface of steel is shown in Figure 14. Adsorption energy was –21,520 J/mol for VCI-A, –22,950 J/mol for VCI- B, and roughly –24,970 J/mol for VCI-C. This energy range is indicative of a good physical adsorption to the metal surface. Generally a multilayer adsorption energy between –5,000 to –50,000 J/mol is defined as a physisorption mechanism , a weak, long-range bonding. However, it can be seen that the interaction of VCI-C with the steel surface is higher than the other inhi bitors, leading to b ett er c orrosion protection. XPS depth profiling analysis showed ~60 to 65 nm of adsorbed inhibitor on the exposed samples, indicating multi- layer adsorption of inhibitor molecules to the steel surfaces. Therefore, the Brunauer Emmett Teller Model (BET Model) is a more realistic adsorption model than the monolayer Langmuir model for this case. 13- 15 But for the adhesion energy calculation between inhibitor molecules and the metal surface, it is appropriate to use the mono- layer Langmuir model. 16 Conclusions This investigation demonstrated that VCI additives can prevent corrosion of CS during and after hydrotesting. When neces- sary, other VCI products can complement hydrotest additives for long-term storage. Electrochemical cyclic polarization showed formation of a stale passive range when these inhibitors were added to the environments. FIGURE 11 Test setup and rating criteria for the NACE TM0208-2018 Standard Test Method. Typical Visual Patterns for Rating VIA Test Results Grade 0 Control No corrosion-protective effect Grade 1 Control Slight corrosion-protective effect Grade 2 Control Moderate corrosion-protective effect Grade 3 Control Good corrosion-protective effect Grade 4 Same as Grade 3 except examined under 10X magnification. Excellent corrosion-protective effect. 57 mm (2.25 in) Bottom of the Stopper A B C D E F G The effectiveness of VCI products is confirmed in various water chemistries including fresh and salt water. The corro- sion rate dropped from ~10 mpy for the salt solution to less than 1 to 2 mpy when var- ious inhibitors were added. The effective- ness of these inhibitors was remarkable in fresh water (less than 0.4 mpy). Tensile post-immersion tests did not show any loss in mechanical properties of the exposed samples. Both strength and duc- tility of the low CS samples were maintained. Adsorption energy was about –21,520 J/ mol for VCI-A, –22,950 J/mol for VCI-B, and roughly –24,970 J/mol for VCI-C, indicating a strong physisorption mechanism (Figure 15). Results indicated that these bio-based, environmentally friendly VCI additives have low toxicity levels and waters containing these VCI products remain safe for many species, allowing discharge according to local specifications. References 1. A.R. Duffy, M.G. McClure, W.A. Maxey, T.J. At- terbury, "Study of Feasibility of Basing Natural Gas Pipeline Operating Pressure on Hydro- static Test Pressure" (Washington, DC: Ameri- can Gas Association, Inc., February 1968). 2. J.F. Kiefner, W.A. Maxey, R.J. Eiber, "A Study of the Causes of Failure of Defects That Have Sur- vived a Prior Hydrostatic Test," Pipeline Re- search Committee, American Gas Association, NG-18 Report No. 111, November 3, 1980. 3. N.P. Zuk, "Course of Theory and Protection from Corrosion," Moscow, Metallurgy, 1976. 4. S.Z. Levin, 2nd European Symposium on Cor- rosion Inhibitors, Ferrari, Italy. 11 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2019

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