This paper describes the efficiency and service life of different VCI compositions and their combinations with desiccants. Some of the methods used to increase the efficiency and service life of corrosion prevention are discussed. Diagrams are shown which demonstrate the relationship between concentrations of VCI and the amount of desiccants in specific atmospheres. These diagrams aid the choice of the combined corrosion protection methods. corrosion, inhibitor, desiccant, efficiency, service life.
More than 1000 VCI compounds are known, but only a fraction of them are efficient, cost effective and environmentally friendly. VCI's are a class of corrosion inhibiting compounds with a finite vapor pressure. The chemical protection is delivered through space by the VCI vapor condensing on a metal surface and creating a protective film.
VCI's 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 [ 1-6].
VCI's have significant properties (Figure 1). The corrosion protection radius depends on the vapor pressure of the VCI's and the temperature. The service life of existing VCI systems is in the range of 1 to 5 years, for example, and depends on the quantity of VCI. The corrosion protection (CP) mechanism depends on the VCI compounds used and the characteristics of the metal being protected. Figure 1 shows the properties of the different types of inhibitors. This understanding allows us to choose the best inhibiting system. There is a need for a system that protects items for a longer period of time than the current VCI methods allow. 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.
The application experience shows that the corrosion protection technology with VCI depends on the following conditions:
- the materials, complexity and size of the equipment,
- the composition, temperature and humidity of the environment,
- the manufacturing technology,
- the storage, transportation and application,
- the required service life and surface quality of the equipment.
VCI films are one of the most widely used technologies for the corrosion protection of equipment produced from ferrous, nonferrous and multi-metal alloys. In most cases, components in a clean and dry condition are protected by VCI film.
Packaging films for industrial applications are produced from low and high- density polyethylene resins and, therefore, are resistant to moisture to some degree. Atmospheric moisture will eventually find its way into a film bag. The presence of moisture in a bag can be expected on surface shipments. Corrosion problems arise when moisture is allowed to enter a VCI bag unimpeded by the film, e.g. through an incorrect closure or a significant hole in the bag. VCI films do not require hermetic sealing. What is required is that the bag be closed such that any air entering the bag must enter through the film, where upon it will be influenced by the VCI in the film. Stapling, taping or folding of the bags is a sufficient closure method. This practice is, however, not always followed.
In all cases, the existing VCI systems' efficacy and service life depends on temperature, humidity, environmental composition, etc. Common aggressive atmospheric components are especially problematic when accompanied by water permeation. That is why it is necessary to consider the extemal temperature and relative humidity when desig
