The combined corrosion protection methods described in this review make the efficient long- term corrosion protection of valuable equipment and structures possible. Existing corrosion protection methods using volatile (VCI) or soluble (SCI) corrosion inhibitors, coatings, or cathodic protection systems (CPS) are generally efficient and have a useful service life. This paper describes the efficiency and the application experience of: VCI compositions in combination with desiccants and gases, and SCI in combination with CPS. These methods are used to increase the efficiency and service life of corrosion prevention. The data presented aids the choice of the combined corrosion protection method.
New methods, which allow the range of VCI applications to be reliably extended, are described. These new technologies increase efficiency and service life and decrease the total cost of corrosion protection of military, automotive and railway equipment, electronic and electrical systems and devices, oil and water storage tanks, tankers, ship enclosures, docks, as well as miscellaneous equipment and metal parts.
More than 1000 types of volatile corrosion inhibitors (VCI) and soluble corrosion inhibitor (SCI) compounds are known, but only a fraction of them are acceptably efficient, cost effective and environment all y-friendly.
VCIs are a class of corrosion inhibiting compounds with a finite vapor pressure. The chemical is delivered through space by the VCI vapor diffusing throughout the enclosed medium and condensing on a metal's surface, creating a protective film. VCIs are useful as part of efficient protection systems for ferrous and nonferrous metals. Many of the applications utilize VCI impregnated polyethylene (PE) packaging, but a variety of other delivery methods have been used. [3-5, 7, 15-19].
VCIs have significant properties (Figures 1, 2). The corrosion protection radius depends on the vapor pressure of the VCIs (Figure 1). The service life of existing VCI systems is in the range of 1 to 5 years. The corrosion protection (CP) mechanism depends on the VCI compounds used and the characteristics of the metal being protected. Figure 2 shows how the different types of inhibitors influence the corrosion process. This understanding allows us to choose the best inhibiting systems. There is a need for a system that protects items for a longer period of time than the current VCI methods. The new methods should retain many of the advantages of the traditional VCI methods. These advantages include self-application of protection, as well as, immediate use of the protected item upon removal from the protection system.
SCIs are a class of corrosion inhibiting compounds, which are useful in corrosive liquid environments such as water solutions, oil and other fluids. These inhibitors in most cases adsorb on the metal surfaces or react with the metal and create an insulating or passive protective film. The best results are obtained using SCI, which increase the corrosion potential of metals. But in some cases the best results can be received by using anodic or cathodic inhibitors (Figure 2). These solutions can be recommended when anodic or cathodic surface areas are very small and the remaining surface areas are resistant to corrosion.
SCIs are used for corrosion protection in neutral, acidic and alkaline solutions. The efficiency of SCI depends on their compositions and concentration. In most cases the concentration required is high and the necessary efficiency can be only be maintained by continuously delivering inhibitors into the environment.
Some SCIs have significant properties (Figure 3) when used in combination with catho
